Crusius, Christian August: Road to certainty and reliability – Oppositions

Crusius moves from subordination – connection of concepts – to their distinction. Two concepts are distinct, he explains, when at least in one of the concepts is found something that cannot be said of the other. This means, Crusius adds, that some type of subordination cannot be found between them.

Distinction as such is not a very interesting notion, Crusius thinks, because types of distinction correspond simply with types of subordination, and furthermore, we can quite easily recognise distinct concepts through internal sense. A more important type of distinction, he says, is opposition, where the existence of one side of the opposition in a certain concept or subject prevents as such or in some measure the existence of the other side. Of opposition, Crusius adds, the most important kinds are the logical and the causal opposition.

The notion of logical opposition, Crusius begins, is based on the notion of logical subordination, where one concept comprehends all the individuals comprehended by another. On the basis of it, we can first define complete logical distinction or diversity, which means, he explains, that no individual comprehended in one concept is comprehended in the other, in other words, both concepts contain some positive or negative determination not contained in the other. If you are wondering, there is also partial logical distinction, which means that there are some individuals of one concept not comprehended under another, but this is not nearly as interesting a relation.

Complete logical diversity can be merely accidental, Crusius notes, if the diversity is caused only by the concepts being formed with different types of abstraction. Thus, he adds, concepts of human and understanding are completely logically diverse, but only because the concept of human is generated by logical abstraction, but the concept of understanding through metaphysical and qualitative abstraction. Then again, if we add the notion of subject to the latter – that is, if we think of something with understanding – we make the two concepts subordinated, because human is something with understanding. On the other hand, concepts of human and stone are completely logically diverse by themselves.

What is completely logically diverse, Crusius points out, might still not be opposed, which still requires that the concepts exclude one another in the same subject. Thus, understanding and will are completely logically diverse, but not opposed, because they can occur in the same subject.

Crusius divides oppositions into logical and real oppositions. Logical opposites exclude one another only in regard to a common concept or genus, so that an individual of this genus can belong only to one of the opposites, even if these opposites can occur at the same time in the same subject: thus, understanding and will can be called logical opposites, because the force that is understanding cannot be will, although a substance that has understanding can have also will. Real opposites, on the other hand, exclude one another from the same substance, like virtue and vice. An even stronger notion is what Crusius calls disparity, where the opposites cannot exist in the same subject even after one another: thus, eternal and contingent are disparate concepts, because what is at some point eterna can never be contingent.

Crusius states that oppositions can also be divided into those between contradictories and those between contraries. Contradictories come always in pairs, he explains, so that always one of them must hold, while the other is negated, like triangle and not-triangle. All other oppositions are those between contraries, Crusius continues, where the contrary opposite might be a partial or determined negation of a concept, like not-angled compared to triangle, or it might posit some substantial determination that excludes the concept in question, like circle compared to triangle. Contraries can thus be positive or negative and there can be more than two of them.

Crusius goes into more detail with the characteristics of contraries. He notes that they can be recognised as opposite either through senses, like sweet and sour, or from their abstract concepts, like virtue and vice. Furthermore, Crusius says, contraries can be merely comparative, where their distinction is based merely on different levels, such as fast and slow movement, but they can be also absolute contraries, so that their distinction is not just gradual, but a certain quality is cancelled through another, like with virtue and vice.  Finally, Crusius divides contraries also in complete or perfect contraries, where one cancels all the properties of the other, like living and lifeless do, and into partial or imperfect contraries, which are opposed only in relation to certain properties, but have many other properties in common, like waking and dreaming.

Moving on to causal opposition, Crusius begins by noting that it could mean that it is impossible that a certain effect would be caused by a certain cause. Then again, he adds, it could also mean that we are speaking of two kinds of activities of certain causes and we know that one hinders the other and cancels it completely or partially or at least modifies it. In both cases, he continues, one can speak either of causes or grounds of physical existence, like warmth and cold oppose one another, or of grounds of moral existence, such as laws conflicting one another. When we are speaking of causal opposites that hinder or modify one another, this might happen through activity, like in case of a collision between two movements, or then they might just prevent some condition of the other, like when our body hinders the consciousness of our own soul.

Crusius, Christian August: Road to certainty and reliability – Causal subordination

The other type of absolute subordination, according to Crusius, is causal subordination, where one thing, called ground, principle, reason or cause, either generates or enables another one, known as effect. The main theme in his writings about this notion is that earlier philosophers – especially Wolffians – had failed to recognise that there are many types of causal subordination and many types of grounds.

Firstly, Crusius begins, a ground can be a real ground, which is a principle of being or becoming: in other words, a real ground generates or enables something outside our thoughts. Such real grounds can be active or efficient causes that cause something through an active force, just like fire burns because it has a force to burn things. Then again, Crusius adds, a real ground can also be an existential ground that makes something else possible, impossible or necessary just by its own existence, without any active force, just like a signet impresses a certain figure just because it is shaped in a certain manner. He notes that in some cases an existential ground has no active force, for instance, when two sides and an angle determine the length of the third side of the triangle. Sometimes an existential ground does have some force, but this just does not affect the respect, in which this something is an existential ground: for example, a flying ball has a force that moves it, but the shape it makes on the sand it hits is determined just by the figure of the ball.

It is then obvious that the same thing can be in one sense an efficient cause and in another sense an existential ground. Thus, Crusius notes, bodies are existential grounds when they determine something through their figure, although the movement enabling the body to be an existential ground is based on some efficient cause within or without the body. He suggests that the same is true of all other things, so that even most perfect activities are in some other sense existential grounds: for instance, holiness of God is an efficient cause, but as an existential ground it restricts the possibility to pardon sins.

Crusius thinks that there can be mere existential grounds, but without the help of efficient causes they cannot generate substances, thoughts, volitions or movement. With such mere existential grounds, the relation is reciprocal, he adds, so that in the case of a triangle we could take any two sides and angle between them and determine the third side from these. Crusius emphasises that this is not true of efficient causes, since we cannot say that e.g. world is the ground of God. In case of an existential ground, the ground and the grounded are necessarily present at the same time, but with an efficient cause, the effect must be generated later than its cause exists, although the cause cannot be regarded as cause, before the effect exists.

In addition to real grounds, Crusius continues, there are also ideal or cognitive grounds that generate in understanding knowledge of something and also conviction of this knowledge. These ideal grounds, he adds, can be a priori, so that through it one knows not just that, but also why something is so, or it can be a posteriori, through which one knows only that something is so.

Crusius points out that something can be in one sense an ideal ground and in another sense a real ground: thus, sometimes we can know from efficient causes their or we can know from existential grounds what they determine. Yet, he emphasises, not all ideal grounds are real grounds, while all real grounds are not sufficient ideal grounds. Hence, ideal and real grounds must be distinguished, and even if one ground would be both at the same time, the distinction would be important, because these two roles of the same ground work in different manners.

Whether ideal or real, Crusius goes on, it is either sufficient for what it is ground of or then it is insufficient. Sufficient efficient cause in particular, he adds, is either fully determined, so that it acts in a certain manner and not otherwise, it is free and not determined to act in a certain manner in all respects. From a fully determined efficient cause, Crusius thinks, it is possible to determine its effect according to all respects, hence, a fully determined efficient cause is also a sufficient ideal ground a priori of its activities and effects. Freely acting causes, on the other hand, can in Crusius’s opinion be only sufficient real grounds, but at least for a finite understanding they cannot be ideal ground. What then is an insufficient efficient cause like? According to Crusius, it either lacks the force to fully generate its effect, or in case of free causes, they don’t want to do it anymore, either because they previously chose a certain goal that they have rejected or because they have just freely changed their volition. 

Crusius also defined the closely related notions of an adequate and an inadequate cause. Adequate cause is a sufficient ground that in the given conditions could not cause anything further, except through what it caused – Crusius notes that this is true of all unfree causes. Inadequate cause, on the other hand, is either not sufficient for more than what is taken as its effect or then it does not want anything more. The example Crusius gives is God, who supposedly is a sufficient cause of the origin of the world, but not its adequate cause: God’s will is enough for generating the world, but God could have created so much more.

Crusius divides causes in general into more distant causes and closer causes – eventually there is also the closest cause, so that between it and the effect considered there are no other causes anymore. Similar notions of distance and closeness can be applied to effects also.

Crusius notes that the effect of a cause can be either absolute or relative. In the latter case, the effect is a change of some relation of a thing, but must be generated through some absolute change in some other thing. Thus, Crusius explains, the Sun causes in the summer an absolute effect by heating the atmosphere, but this increasing warmth causes only a relative effect in making a cellar colder than the air outside it, because the temperature of the cellar has not absolutely decreased.

Cause can be a cause in itself, Crusius states, so that this type of cause either always or at least regularly generates certain effect. It can also be an accidental cause, where only an accidental combination of circumstances leads the cause to produce the effect. Thus, Crusius explains, when a doctor gives to patient a regularly used medicine, this medicine is a cause in itself of curing the patient, even though it wouldn’t do it by itself. On the other hand, if the doctor happens to choose a wrong medicine and it still happens to be effective, the error is only an accidental cause of the patient being cured.

Crusius notes that a cause in itself can have different grades and it can be a cause in itself only for certain circumstances of the effect. One particular type of a cause in itself he mentions is what is called causa sine qua non, which is insufficient for generating an effect, but necessarily required for this. Yet, Crusius notes, this is not enough for calling something causa sine qua non: we should not take something as a cause in itself (and thus, not even as a causa sine qua non), if it is positively directed to generating or enabling a certain effect, but this same activity inseparably enables another effect, which the efficient cause has not wanted, but just was physically unable to hinder. The purpose behind this restriction is to show that God is not a causa sine qua non for sin: God made humans free, in order to enable moral virtue, and the possibility of sin was just a necessary concomitant. God could be called an accidental cause of sin, Crusius admits, but this does not incur any moral responsibility.

Crusius explains that if a thing is generated as an effect of certain causes, it does not follow that also its continued existence and its characteristics during its existence must depend from the same causes. Indeed, he emphasises, the continuing of a contingent thing requires at all moments a positive cause, thus, the survival of simple things requires divine conversation, and survival and characteristics of things dependent on simple things depends on the survival, characteristics and combination of them. These considerations lead Crusius to suggest some particular rules.

Firstly, when one is explaining an effect and searching for its sufficient ground, one must look for all three points and ask for the sufficient cause of the origin, continued existence and characteristics of the effect. Secondly, a true real or ideal ground of an effect might still be a sufficient ground for only one of these circumstances or even only for part of it. Thirdly, no finite substance in the world is a sufficient cause of an effect in respect of all the three circumstances, because the continued existence of the cause itself is dependent on many other causes that also have an influence on it. Fourthly, with regard to each circumstance should always be distinguished the causes of its possibility and actuality. Finally, with the enabling causes should again be studied which of them are active efficient causes and which are mere inactive existential grounds: for instance, lack of obstacles is an existential ground enabling self-improvement, while an active will to improve oneself is an efficient cause enabling it.

Causal relations depend ultimately, Crusius says, on substances that act on their own forces. These causes, he thinks, deserve to be called principal causes, while other causes are mere abstractions from principal causes. A principal cause, Crusius continues, is either matter or spirit. If it is matter, it is either a physical cause in the strict sense that causes its effect through an active moving force or it is a mechanical cause that determines its cause through the figure and position of its integral parts: thus, fire is a physical cause, while hammer is a mechanical cause. Crusius notes that all material effects involve both kinds of cause, because at least the figure of small particles influences the effect and a mere figure by itself could not have any effect without a moving force.

If a principal cause is a spirit, Crusius continues, it acts either through mere understanding or through will acting according to certain ideas. Furthermore, he says, its activity is either immanent, that is, affects only something within the spirit, or transient, that is, affects also something outside it. If the spirit in question is not free, Crusius calls it a spontaneously acting cause, and if it is free, he calls it a morally acting cause. Finally, he notes, even spiritual causes can be called physical in a more extended sense, so that any principal cause that is not mechanical would be physical.

Crusius goes through a list of causal abstractions, which are thus all separated from principal causes. First of these abstractions is a force, by which he means a property of some subject to make another thing possible. Such a force is either active force, attached to an efficient cause, or an inactive capacity, attached to a mere existential ground. When the force is actually generating something, Crusius explains, it is said to be in action. When the action generates something, the thing in which something is generated is called an object, which is then said to be in a state of passion. A passive object can be either completely passive or only partially passive and thus have its own internal activity, like a flame that changes its direction due to the effect of wind.

Because many principal causes and causal abstractions can be involved in the same causal relation, Crusius points out, we need terms to describe such an interaction of causes. Firstly, the causes can be coordinated, so that none of the causes can be regarded as more important than the others. Then again, Crusius adds, one of the causes can be a primary cause, because it contributes most to the effect. Other causes can then be called adjunct causes.

An important type of adjunct cause is that of subordinated or intermediate causes, by which Crusius means causes, through which another cause generates its effect. Such a subordinate cause might contribute something to the effect through its own force or it might be a mere condition enabling the effect. Furthermore, Crusius adds, it can act positively, generating circumstances, on which the effect depends on, or it can merely remove obstacles of the effect. Finally, the subordinate cause might be necessary for producing the effect, it might be a facilitating cause that regularly helps to produce the effect or it might be just a subsidiary cause that only occasionally helps the effect,

An important distinction under the subordinate causes is that between ministerial and instrumental causes. By a ministerial cause Crusius means a moral cause that is in its dignity not of a higher level than the cause using it: a primary example would be that of a ruler using their minister to make something happen. In the rare case of a minister using their ruler to do something, he adds, the ruler should not be called a ministerial cause, due to the ruler being of higher dignity, but a subordinate principal cause of the effect, which then forms a third possibility in addition to ministerial and instrumental causes. An instrumental cause, Crusius explains, is a subordinate cause that is not a moral cause. It can be active, like light, or passive, like a pen.

Another important type of adjunct cause is an impulsive cause that spurs another cause into activity. Such an impulsive cause can be merely material, so that its movement makes another material force active, or it is ideal, so that its activity involves a substance acting according to some ideas. An ideal impulsive cause, Crusius explains, can be itself a spirit, say, when a soul puts body in action, or it can be an impulsive cause in the strict sense, that is, when it puts some spirit in action, like when a spur makes a horse run. Such an impulsive cause in the strict sense can be either internal or external to the spirit in question. Furthermore, its effect on the spirit can happen through moral means, like when a speaker motivates someone to a decision, or it can act through ideas, but without generating a free activity, such as when certain sensations in the body make us sad. Crusius also calls the former sort of impulsive cause a moral cause, in distinction from any other efficient cause that he then calls a physically efficient cause.

Morally acting causes involve their own particular causal abstracts, Crusius notes. Such a cause strives toward some purpose or goal and uses some means, if the obtaining of the goal is not immediately in their own power. If morally acting causes have reason, striving toward a goal happens with decision and consciousness. Indeed, Crusius says, in a more strict sense only reasoning spirits have purposes and goals Such a spirit thinks about its purpose or goal before the means, but reaches the means before the goal.

Crusius distinguishes between different senses of the term purpose. Firstly, it can refer to a subjective purpose, which is a need felt by an active spirit. Secondly, it can refer to an objective purpose, which is the representation of the object that is needed. Finally, it can refer to a formal purpose, which is a relation of the object toward the spirit that desires it.

Purposes form series, Crusius points out, so that it is possible to distinguish between closer and more remote purposes. Particularly a purpose can be the highest or final purpose, while other purposes are intermediate in relation to it. All of these purposes, Crusius adds, are also impulsive causes for what the spirit does because of them: particularly a higher cause is an impulsive cause for lower purposes. Still, he adds, the concept of purpose still differs from that of impulsive cause, because there are other impulsive causes that do not act as purposes, but merely af efficient causes generating some need in the spirit. An example of such an impulsive cause, Crusius suggests, would be good works that spur one to love a person, although these good works are not the purpose or goal of the love (at least if the love in question is pure).

Crusius proceeds to divide the notion of means. Firstly, he says, we can distinguish between material means, that is, the particular intermediate cause the acting spirit uses for achieving some purpose, and formal means, that is, the way in which the acting spirit uses the material means. Crusius also emphasises that all intermediate causes are not means: for instance, when a wind rises during a battle, making smoke and dust fly into the face of the enemy, the wind is an intermediate cause of one’s victory, but not means to it, unless the circumstance is consciously taken advantage of.

Just like all intermediate causes, means can also be divided into those that generate the effect wholly or partially through their own force (Crusius calls these causative means) and those that are mere conditions required for generating the purpose: for instance, a motivational speech used by a leader to drive their army to battle is causative means, while the necessary equipment provided by the leader are mere conditions. Crusius notes that in the case of purposes with God as their efficient cause, created spirits are always at most conditions and not causative means, but it just makes the perfection of God more apparent, when no causative means are required.

Crusius thinks to have shown in his practical philosoy that the choice of purposes and means is regulated, on the one hand, by prudential obligations derived from the nature of purposes themselves, and on the other hand, by obligations legislated by the divine will. These rules then define the limits of what Crusius calls moral possibility (that something may happen), moral existence (that something should happen) and moral impossibility (that something should not happen). All of these characteristics, he adds, have their real and ideal grounds, thus, grounds in general could be divided into the grounds of physical and the grounds of moral possibility and actuality. These two types should not be confused, Crusius warns: a cause motivating us to do something is not by itself a ground obligating us to do something.

Crusius, Christian August: Road to certainty and reliability – Existential subordination

Crusius divides existential subordination into five classes, corresponding to kinds of abstraction. Firstly, he says, we have external subordination, where one idea or concept is externally abstracted from the other, like a place where a person lives is abstracted from that person. Secondly, we have metaphysical subordination, where an abstraction subsists in something concrete, like a figure in a body. Thirdly, we have mathematical subordination where an abstraction relates to something concrete as its integral part, being either continuous or discrete quantity, like 10 is a part of 100. Fourthly, we have a qualitative or physical subordination, where an abstraction relates to something concrete as a part that is not regarded as a magnitude or figure, but as a substance or a physical quality. Finally, we have logical subordination, where one individual is comprehended under another, like a human is related to a substance.

Crusius takes a closer look at logical subordination, because all other cases of existential subordination can be turned into logical subordination. Thus, he says, one should investigate whether logical subordination is such in itself or only contingently: for instance, when we say “human has a head”, this is not a case of logical subordination, but we can turn it into a logical subordination by saying “human is something that has a head”. Furthermore, Crusius is adamant that the difference of various kinds of subordination is important and therefore other kinds should not be transformed into logical subordinations: if I say that a soul has an understanding (metaphysical subordination), I do not mean that soul is an understanding (which would be logical subordination, if it were true).

What the elements of logical subordination or logical abstractions are, Crusius explains, is representations of a set of individuals ignoring their individuality and showing them as similar: in other words, they are names of similar individuals. Such a logical abstraction, he adds, does not designate only a part of a concrete individual, but the whole individual. Furthermore, although only a part of its properties is selected to designate the whole, these properties are not regarded as independent, but as attached to a subject: for instance, Crusius suggests, in a concept of a scholar one thinks of a subject according to a certain quality, but when I say scholarship, I regard the same quality in abstraction from any individual subject. Hence, I can say that many people are scholars, but not that they are scholarships.

Crusius notes that logical abstraction can be regarded in two ways. Firstly, it can be regarded essentially or materially in regard to its essential content, that is, in regard to ideas thought under it. Secondly, Crusius adds, it can be regarded in relation to extension, that is, in regard to the set of individuals, which can be named by it. The more extensive a logical abstraction becomes, the less ideas one thinks in it, since otherwise it couldn’t name so many things that are dissimilar in many respects.

Logical subordinates, Crusius continues, either comprehend all individuals belonging to each other or then one or the other is more extensive than the other. In the latter case, he continues, the more extensive is called genus, while the other must then be species. A genus, Crusius divides, is either an essential genus by itself or contingent genus by accident. In the first case, all individuals subordinated to the genus belong to it essentially, even when regarded without particular purpose, as when substance is a genus of humans. In the second case, he compares, some contingent property is chosen arbitrarily and changed into a genus: for instance, when I say that all scholars are either sick or healthy, this does not mean that all sick people would be scholars, but only that sick individuals known to be scholars are scholars.

Crusius goes on making distinctions by noting that a genus is either a distant one, where there is always a possibility for an even closer genus, or a closest or proximate genus, where there isn’t such a possibility. Since the series of distant genera cannot be infinite, Crusius argues, there must also be the highest genus (thing in the most extensive sense of the word), and in relation to it all others are middle or subaltern genera.

Genus can be either a pure or an impure abstraction, Crusius muses. Furthermore, it is either homogenous or heterogeneous concept. A homogenous concept belongs to all its species or individuals in a completely same sense, for instance, human is animal in the same sense as dog, because both have body and soul. A heterogenous concept, on the other hand, does not belong to all its species or individuals in a completely same sense. Thus, although a certain similar part of concept might be a reason why the concept belongs to species or individuals, some species or individuals might add new circumstances and modifications of the same general concept: for instance, snowing in winter is said to be possible because of natural causes, but golden mountain is said to be possible, because it contains nothing contradictory.

Crusius notes that what holds of a genus, must hold also of species and individuals under it. He makes this statement more accurate by noting that its message concerns actually just pure genera: others it concerns only under the conditions, in which they are genera. Crusius also insists that before applying heterogenous genera to some individuals, these genera should be divided and their heterogeneity should be recognised, because otherwise one could apply to some of its individuals what could be said only of others – for instance, golden mountains could be called possible without explaining what type of possibility is meant.

Species is generated from a genus by adding an accident to the concept of genus. This accident, Crusius explains, can be either something that is in itself a determination, like the sameness of all sides in a triangle, or something that is made contingently into it, like clothes in a human being. The accident in question, Crusius continues, can be something that is found in all individuals belonging to it, like reason in a soul, or it is an external abstract, like time.

Crusius divides accidents into proper and common accidents. A proper accident does not belong to all existing individuals generally or at all times, but still cannot belong to individuals or species under other genera: in this sense, Crusius insists, virtue is a proper accident of entities with reason. A common accident, on the other hand, can also belong to individuals of other genus, just like being sick is a common accident of humans, because other beings beyond humans might be sick.

When a species is made by adding an accident to a genus, Crusius explains, either to each species is added another positive accident (say, when thinking and moving are suggested as species under the concept of action) or it is added only to one, while others are assumed to lack it, just like in the case of passive and active matter.

Crusius notes finally that an accident might imply in individuals no other difference but such that consists only in another state of the essence and depends on the different grade and direction of its forces and on the different relations of things toward another. He calls such an accident natural, because nature itself has made it into an accident, like speed or slowness of movement. On the other hand, Crusius points out, the accident might not be enough for distinguishing subordinated things: this he calls an arbitrary accident.

Crusius, Christian August: Road to certainty and reliability – Subordination of concepts

Crusius defines subordination or combination of concepts as a relation where one concept is where the other is also, at least under certain conditions. Subordination involves thus always two concepts: one of them is concrete, from which the other is abstracted, or then both concepts can be abstracted from one another.

Crusius divides subordination into relative and absolute subordination. The difference is rather simple: in a relative subordination, the subordinated concepts are represented through a predicate describing a relation (an example would be concepts of high and low), while an absolute subordination involves a natural combination of things that is not derived from the structure of our concepts (an example would be concepts of soul and understanding). Looking first at the relative subordination, Crusius notes that it concerns either an arbitrary relation, like that of people standing in a line, where one could begin from either end, or it is founded on something based on things themselves, for instance, when a mountain is designated as large and house as small compared to it.

Crusius also notes that from every absolute subordination could be abstracted a relative subordination, so that same concepts could be regarded as both relatively and absolutely subordinated: his example is that of father and son (a relative subordination), which involves also an absolute subordination of cause and effect. This means, he explains, that while sides of relation must exist at the same time, insofar as they are related (otherwise they wouldn’t be related), their absolute essences might still involve a difference of temporal priority: for instance, while parent as a parent must always have a child (otherwise they wouldn’t be a parent), parents still have existed before their children (just not as parents).

Such a temporal priority is not the only possibility, Crusius explains, but there could also be just a natural priority between concepts in a relative subordination: his example is divine understanding and divine will, neither of which can have existed without the other, although understanding is by nature prior to will. The final possibility, he concludes, is that the two concepts are just temporally simultaneous and by nature of equal worth, like two lines similar to one another.

I shall take a closer look at the different types of absolute subordination in later posts. For now, suffice it to say that Crusius divides absolute subordination into two classes: causal and existential subordination. He notes that this division is not completely exact, since causal relation can be arbitrarily represented also as existential subordination, say, when instead of pointing out that sun causes light we insisted on saying that sun is a light-giving body. Because of this possibility, Crusius concludes, we must be able to differentiate cases where concepts are by their nature existential abstracts from cases where they involve causal subordination.

Crusius, Christian August: Road to certainty and reliability – Divisions of concepts

The first element of thinking, Crusius states, is concepts or ideas. Concepts represent an object that differs from the concept, through which the object is thought, he adds. There are various ways to divide concepts, and the first way Crusius mentions is that according to the cause behind the concept: concept can be a sensation that represents an object, insofar as we sense it, or it can pertain to a memory, by representing something that we do not currently sense. The latter kind of concepts, he insists, are merely retained sensations or they are generated through imagination or through judgement or through both.

As to their content, Crusius continues, concepts can represent either individuals or abstractions. Abstract concepts, he notes, are also called predicables, because they are something that can be predicated of individuals. Individual concept is then simple or complex, depending on whether the individual in question is simple or complex. Individual can be represented through a sensation or it can be called by a name taken from an abstract idea.

Concept may also, Crusius adds, represent an absolute thing or a relative thing. The essence of a relative thing, he explains, consists of a relation, that is, of a concept that is abstracted from two or more things in such a manner that in it is represented something that could not be abstracted from one alone – Crusius exemplifies relative things with the concept of error. Then again, when thinking of an absolute thing, we should be thinking of something more than just concepts that belong together only because one has abstracted from several things at the same time. In other words, Crusius explains, an absolute thing is a unity not just because of our abstraction, but also outside our thought.

Absolute things represented in absolute concept are, Crusius recounts, physical, mathematical or merely existential beings. Physical things, he adds, are substances (like soul) or their active forces (like understanding) and effects (like light). Then again, mathematical beings are such that are determined merely through the type and magnitude of extension. Crusius notes that not all mathematical beings are absolute, but only such that are thought without relation to something else, like ball or triangle. Finally, mere existential beings are not active forces or substances nor magnitudes, but only some properties, regarded as possible or existing, such as immortality, space or property in general.

Crusius divides relative beings into moral, mathematical and relative beings in a strict sense. By moral beings he means such relations of things that they have toward purposes of a willing spirit, that is, relations that are means making certain goals possible or actual. If certain things are considered according to moral relations, Crusius notes, these concern either moral actions or things that are not as such moral, but that are connected to certain moral relations, like gold used as money or bills of exchange. Moral actions, he adds, are regarded either only as actions in general, without any indication of their goodness or badness, or they are represented as virtue or vice, prudence or stupidness.

Relative mathematical beings, Crusius notes, are magnitudes related to other magnitudes, such as square roots or sines. An important type of relative mathematical beings, he says, are mechanical beings that are appropriate for a determined purpose through the figure and placement of their parts, such as weight or barometer.

Finally, Crusius defines relative beings in a strict sense as certain parts or conditions that are taken together in one concept because of considerations of a thinking understanding, but where the relation in question does not occur between magnitudes or goals and means: an example of such a strict relative being is truth. He notes that relative beings in a strict sense include concepts that represent wholes, parts of which belong together only because of a certain consideration of an understanding, such as a poem or a speech.

Crusius notes that relative concepts representing relative things follow certain rules. Firstly, it is very convenient to distinguish them from absolute concepts, because otherwise errors occur especially in morality, for instance, when good of things is held to be absolute. Crusius insists also that relative things should not be understood as always of lesser importance than absolute things, since this depends on the issue in question: for example, it depends on the relation that creatures have toward God, whether they are in happy or unhappy condition. Then again, he notes, all relative entities presuppose certain absolute entities, that is, substances, forces and properties, without which relations would not be possible. Thus, Crusius concludes, we should distinguish in things their absolute and relative essence.

In case of abstractions, Crusius continues, we can think of not just their essence, but also the manner of abstraction, through which we isolate them in thoughts and regard them as particular concepts. Thus, we can distinguish material from reflected concepts. By material concepts Crusius means concepts that represent a certain object that is something else than a manner of abstraction, for instance, light. On the other hand, reflected concepts represent the manner of abstraction, according to which we regard certain concepts, such as genus and species. Some concepts belong to both classes, depending on the viewpoint, for example, substance can be regarded as a material concept, when we think it as a combination of a subject and a force, or as a reflected concept, when we think it as a genus of humans.

Crusius divides concepts also into determined and undetermined. A determined idea contains in itself such determinations, without which it cannot be thought completely and distinctly, while an undetermined concept lacks some determinations that are required for thinking it distinctly and completely. An undetermined concept, Crusius explains, is thought either in an obscure manner or then the thinker attaches to it some possible determinations that they have perceived in an example. Even if we do not know positive determinations of a concept, he adds, it can still be useful to represent what it is not and to determine it thus negatively.

Crusius explains that a concept is undetermined only, if it lacks such determinations that do not concern our arbitrary manner of consideration: thus, a concept of a human being can be perfect, even if we knew nothing about their clothing. Still, he adds, no other concepts are fully determined, except those representing individuals. With other concepts, Crusius thinks, they are to be regarded as determined, if they contain as many determinations as the purpose requires, so that one ignores other determinations, because they are arbitrary to the purpose.

As long as necessary determinations are lacking in a concept, Crusius states, it is partially unknown to us and thus a mystery. If a concept is not even negatively determined, so that it cannot be distinguished from anything else, it is of no use. Crusius thinks that if we add to a concept that we cannot determine some possible determinations just for the sake of distinctness, while remaining aware that these are only possible, but not necessarily true determinations, this does not harm truth, but is useful and often necessary.

Concepts represent an object, Crusius notes, but this object can be something outside our thought – the represented thing that is thought under certain properties for the sake of distinguishing it from other things – or then something inside thought – the representation of properties, by which the thing outside thought is designated. When we thus compare two concepts they can be objectively different, when one has another object outside thought than the other, like human and cow or love and hate, they can be ideally different, when they have the same object outside thought, but represent it through different properties and for different purposes, like rational creature and creature obliged to virtue, or the two concepts can mean exactly same.

Crusius divides concepts also into concrete or unanalysed concepts, analysed abstract concepts and simple concepts. Concrete or unanalysed concepts consist of a manifold of parts and properties, which are not precisely distinguished from one another: they might be represented through an example of this concept, but not thought with distinct separation. Analysed abstract concepts represent a distinct differentiation of their parts and separate such that essentially belongs to it from others, just like in most definitions. Finally, since the analysis cannot go on infinitely, we find simple concepts that cannot be analysed further. A concrete concept, Crusius suggests, is either not yet analysed or then human understanding cannot analyse it at all.

In relation to their usefulness or application, Crusius notes, concepts divide into characteristic and uncharacteristic. A characteristic concept helps to know and evaluate an example, while an uncharacteristic concept does not do this. Thus, Crusius explains, arteries can be defined as blood vessels that lead blood from heart to organs, but this is not a characteristic concept, because one still requires other signs for recognising arteries in the anatomy of the body.

Concentrating on the abstract concepts, Crusius divides them into a priori and a posteriori abstractions. In case of a priori abstractions, it is possible to know merely from the essence of the thing or from a comparison with the essence of God, why it must or can belong to something: for instance, this is the way we know that a human being is obligated to be virtuous. In case of a posteriori abstractions, we know only a posteriori that these abstractions belong or can belong to a thing: for instance, when we consider a colour or length of something.

Crusius divides a priori abstractions further into hypothetical and absolute a priori abstractions. Hypothetical a priori abstraction is abstracted as a part from a presupposed concrete concept, for instance, when we abstract the concept of a middle point from that of a circle. On the other hand, an absolute a priori abstraction is understood as inseparable from what it is abstracted from, for instance, when we regard humans as obligated to virtuous action.

Crusius notes that abstractions can also be divided into perfect and imperfect abstractions. Perfect abstractions can be thought without a connection to other abstractions from the same individual: thus, for instance, intelligence is a perfect abstraction in comparison with virtue, since one can be thought without the other. On the contrary, while an imperfect abstraction can be distinguished from any other abstraction, when they are thought together, there still are some other abstractions that cannot be separated in thought from the original: Crusius gives as examples the concepts of subject and force.

Crusius suggests that perfect abstractions can be thought without one another and they are ideally separable, although there can be other reasons why they are not really separable. On the other hand, imperfect abstractions can be distinguished and they are discernible, but they still must be thought together. With many imperfect abstractions, the relation is reciprocal, like with the concepts of subject and force. With others, the relation is one-sided, for example, will cannot be thought without understanding, but understanding can be thought without will.

Finally, Crusius divides abstractions into pure and impure. Pure abstractions are abstracted not just from the object, but also from essence naming it: for instance, the concept of understanding is a pure abstraction from the concept of a reasoning being, since it belongs to the essence of a reasoning being to have an understanding. On the other hand, impure abstraction is abstracted from individuals with a certain essence, but not from this essence: for example, mortality is an impure abstraction from the concept of a reasoning being, since a reasoning individual can be mortal, although it is not part of the essence of an reasoning individual that it must be mortal. Crusius explains that we need this distinction, because otherwise we might think that we have defined an essence, when we have just pointed out a property distinguishing individuals with that essence from others (thus, I cannot define willing substance by its having sensations). Furthermore, he adds, arguments holding of essence might not hold of impure abstractions, for example, God wills our happiness, because we are reasoning creatures, but this does not imply the happiness of our animal side.

Crusius, Christian August: Road to certainty and reliability – What understanding can do

Crusius defines understanding in the wide sense of the word as any ability of a substance to have ideas. In finite spirits, he explains, understanding consists of many fundamental capacities, thus, understanding is the sum of such capacities, by which a finite spirit represents something. Crusius notes that we also have a more restricted notion of understanding, which refers only to higher capacities of understanding that has achieved the level of reason.

Reason Crusius explains to mean such a grade of perfection of understanding that is it is capable of consciously knowing truth as truth. In finite spirits this means such a sum of cognitive capacities that enable conscious knowledge of truth. Crusius notes that we can speak of reason in another sense, as a sum of truths that can be known through the power of reason in the first sense, just from the consideration of natural things.

Reason in both senses, Crusius explains, can be regarded concretely, as it is found in a certain individual, or abstractly, when its essence is regarded in itself and the subjective conditions of particular persons are ignored. Thus, we get four different meanings for the word reason. Firstly, we have a concrete capacity of reason found in a particular subject. Secondly, we have the abstract human reason, which means the sum of essential capacities of human understanding in general, together with the effects that these capacities enable in themselves. Thirdly, we have the concrete sum of reasonable truths, known and considered as reasonable truths by a particular subject. Finally, we have the abstract sum of truths that can be known from the consideration of natural things through experience and correct deductions. Crusius notes that part of the truths included in the final sense of the reason might still be unknown to all humans, due to insufficient sensations and deductions.

The opinion of Crusius is that the first fundamental capacities of human understanding cannot be discovered, thus, that we can only distinguish capacities dependent on and derived from these fundamental capacities, as distinctly and in as orderly fashion as possible, and show how these derived capacities follow one another or receive new determinations through their use. Hence, he suggests as his next task to find the least complex cognitive capacities that we can know. These capacities Crusius will then call the main cognitive capacities and he will derive from them more complex capacities.

Crusius takes as the first main cognitive capacity sensing (Empfindung), which he defines as a state where understanding is immediately necessitated to think of a certain object as existing and present, so that the presentation of this thing is not first generated from other concepts through a deduction. Due to this immediacy, he explains, ideas of sensing or sensations are much livelier than others. Distinct sensations, Crusius states, engage understanding fully, and when we are dreaming, our representations are not distinct enough so that liveliest of them are confused with sensations, until we wake up.

Crusius divides sensing into external and internal sensing. In external sensing, he explains, we sense something that we represent as being outside the soul, while in internal sensing, we sense something that we represent as in our soul. Crusius identifies internal sensing also with the capacity of being conscious. Through internal sensing, he points out, we sense that we think, parts, properties and relations of our concepts, and certain activities and conditions of our will. Internal sensing does not then involve anything that happens in our body, which Crusius takes to be a type of external sensation. He also differentiates sensation from perception, which means either any representation at all or then a condition of understanding where representation becomes lively or we start to become conscious of it.

Both external and internal sensing, Crusius tells us, direct themselves in accordance with certain conditions of our body and are connected with certain changes in it, which is one reason why we know our body before others. External sensations correspond to certain organs in our body, and as long as the organs are in good condition, the sensations appear when the present objects cause changes in these organs. Thus, Crusius argues, not just the possibility and actuality, but also the characteristics of external sensations correspond positively to certain conditions in our body.

On the other hand, Crusius insists, characteristics of internal sensations do not follow the body, but their possibility and actuality and the reason for their ease and liveliness are negatively connected to conditions of the body. In other words, when our body is in bad condition, our internal sensations might be hindered. Crusius explains that for this reason babies and old people cannot think well and violent movement of bodily humours can hinder our thinking. Still, he says, because conditions of bodies can be only movements and representations are not movements, conditions of our bodies are not causes of representations.

Since causal relations cannot be sensed, Crusius explains, experience cannot tell generally what is the reason for the constant conjunction of changes in the body and changes in the understanding. He is still adamant that we need not assume an occasionalist explanation for this conjunction. Indeed, Crusius is very much against the idea, since occasionalism would make God the originator of sin and because it is connected with what he takes as a ridiculous hypothesis that animals are mere machines.

Crusius is equally critical of the Leibnizian idea of pre-established harmony. Indeed, he suggests that metaphysics has shown that matter and finite spirits must necessarily truly affect one another, because otherwise the existence of the world would have no purpose. Furthermore, Crusius thinks that mere mechanical structure of the body can only enable, but not cause certain movements in our bodies. He also finds it problematic that pre-established harmony would mean that the soul will fall into eternal sleep, after its body has been destroyed, unless it somehow gains a new body.

After all these considerations, Crusius is certain that there occurs some real interaction between soul and body and that this interaction at least enables sensation. Still, he notes that it is not the case of movements affecting our sense organs changing directly into ideas of soul, since ideas are spiritual activities, not physical movements. Furthermore, Crusius is convinced that sensations – or ideas in general – are not outside our soul nor things between substances and accidents that we just observe.

Crusius begins his own explanation of the interaction by noting that we can observe sensations directing themselves according to certain states of body. He has also argued in his metaphysical writings that souls can move, which explains the possibility of matter and soul interacting. Bodily movements cannot directly generate sensations, Crusius thinks, because then the effect would be more perfect than the cause. Similarly, he suggests, an idea cannot be the closest nor sufficient cause of motion, because an idea contains only activity for representing something in understanding and does not by itself enable activity outside the soul. Crusius concludes that when an idea seems to follow bodily motion, this motion is a condition, the presence of which enables an idea to be generated through a mental activity. When a bodily motion appears to follow an idea, this motion must be generated as an additional state from the effect of a mental activity caused by the idea.

With the particular case of external sensing, Crusius determines further, movement in the organs of external sense causes a movement in the substance of soul through stirring of nerve fluid, because movement can only cause movements. This movement in the soul is then a condition for activation of some mental capacities that are true effective causes of representation. Crusius explains that we cannot further determine this process, since we are unable to sense what is simple and even the smallest organic parts of sense organs are still greater than the fluid matter in nerves and the smallest movements of its parts. In addition, he states, deductions can at most convince us of the existence of this process, but not reveal its further characteristics. In any case, Crusius thinks, laws of external sensation are contingent, and God could have provided us with very different sense organs: more perfect spirits follow more perfect laws of sensation.

In case of internal sensing, Crusius adds, the process is somewhat different. When the soul consciously thinks, it posits its own substance in movement. In other words, Crusius explains, the mental activity generating our consciousness is combined with another that causes a certain movement of the substance of the soul. This movement should be able to push away the matter surrounding our soul, and if this isn’t so, our consciousness can be completely or partially hindered. Determined characteristics of this movement cannot be known, Crusius notes, but its effects can be felt on our foreheads.

Crusius answers the objection that so many motions of the soul could not all co-exist with the assumption that these movements are quick like lightning. He also counters the objection that the soul should have unnaturally precise knowledge of the direction of these movements, in order to not be mistaken of them, by suggesting that it is not absurd to ascribe to soul ideas of all the motions it produces in the body. The soul is not just conscious of them: every soul must have an idea about its body, in order to be alive, but consciousness requires further conditions and need not be connected with all ideas.

Sensing, Crusius thinks, is our first and original cognitive capacity, providing a basis for all our thoughts: we are combined with a world and form a part of it and this combination happens through our own body, so that the activity of our thoughts must be combined with the movement of matter in and through our body. On the contrary, he adds, God requires no such conditions and hence perceives things in a completely different manner. Indeed, Crusius insists, God could create beings that did not need sensations for thinking and the Bible suggests we will have such cognition in the next life.

The second main capacity of understanding Crusius mentions is memory or the capacity to continue having ideas that have already existed. In other words, memory either retains for a while the original vividness of ideas, or after this vividness has diminished, reproduces it wholly or partially under certain conditions. We need memory, Crusius explains, because otherwise we couldn’t use our ideas further: we know only as much as we have in our memory.

From memory and internal sensing, Crusius notes, is generated our capacity to recollect or to recognise that an idea is the same as the one we had earlier. This recollection requires memory, so that we can have earlier ideas, and internal sensing, so that we are conscious that an idea is the same as earlier. Crusius is careful to distinguish this human power of recollection from the general capacity of memory that makes an idea lively also in the absence of its object and thus makes an animal having this idea act like the object would be present. Because internal sensing requires bodily efforts, he adds, recollection also requires bodily efforts.

Crusius explains that we need not assume any special fundamental force behind our capacity of memory: every idea is an activity with a certain grade of strength and duration, and just like in physics movement tends to continue, if nothing hinders it, same holds of ideas as mental activities. Still, Crusius emphasises, since we do not know the ultimate constituents of mental activities, we cannot say whether memory is based on just one or many fundamental forces.

Third main capacity of understanding, Crusius says, is judgement or the capacity to use one’s thoughts for the purpose of evaluating what is true and false. Judging presupposes sensation and memory, he notes, but also a capacity to distinguish one idea from another. Judgement could then be taken also as a capacity for making division of ideas. Through such a division, Crusius explains, a part or condition of an idea is regarded by itself in its isolation and differing from others. In other words, it involves abstracting, that is, isolating a concept in thoughts from another, in which it is contained or to which it is connected, and regarding it by itself. Abstraction does not destroy the whole, Crusius points out, but merely highlights some aspect of it.

Abstraction does not work in isolation, when judging, but only in connection with internal sensing or consciousness. Thus, Crusius explains, if the effects of judgement lack a sufficient grade of consciousness, understanding cannot make use of it: it doubts and does not make decisions. Furthermore, he adds, because irrational animals do not have consciousness, they cannot make judgements, even if they would have as fine ideas as humans. Finally, Crusius notes, because internal sensing can make our body exhausted, it is understandable that a really concentrated judicious meditation meddles with the force of our body.

Crusius divides abstraction into causal abstraction, which differentiates thing generating or enabling from thing generated or enabled, and existential abstraction, which differentiates things, which are together or follow one another without one generating or enabling the other. Furthermore, he divides existential abstraction into logical abstraction, which starts from individuals, but ignores individuality in thoughts, generating a universal concept (e.g. abstracting a concept of human in general from individual humans), external abstraction, which separates something from its external conditions or relations (e.g. abstracting a place and time from a human being), metaphysical abstraction, which distinguishes characteristic from its subject, (e.g. abstracting humanity from a human being), mathematical abstraction, which differentiates manifold into integral parts (e.g. dividing body into two parts) and physical abstraction, which differentiates manifold into non-integral parts (e.g. dividing soul into understanding and will).

The final main capacity of understanding Crusius mentions is ingenuity or the capacity to make discoveries by moving from one idea to a new, but connected idea, but not through abstracting division.This ingenuity, he explains, is not the capacity to perceive or affirm possible connections, which requires mere judgement. Indeed, Crusius adds, it is the hardest capacity of understanding to explain, and there’s less to learn about its fundamental essence. It might well be, he surmises, that in the hidden essence of ideas lies something that awakens a similarity with other ideas and thus unites them. Since such a process does not require consciousness, Crusius explains, animals might have ingenuity.

After the least complex capacities of understanding Crusius moves to the most important derived capacities, one of which – recollection – he has already mentioned. After it, the first derived capacity he mentions is the imagination, which is a capacity of using a lively idea in making other ideas lively. Crusius notes that rational beings imagine consciously, but in irrational animals the imagination has a true effect on determining their actions. He also divides imagination into imagination of memory, which reawakens ideas that have been thought earlier, and imagination of ingenuity, which awakens new ideas.

Next derived capacity Crusius investigates is the capacity to develop imperfect ideas by making them more determined, somewhat like colouring a pencilled sketch. He notes that it involves more than just making ideas more distinct, which requires nothing else but judgement. Crusius divides this capacity into two types: first of them involves positing from a concept of cause its nearest effects, for instance, in discovering causal deductions, while the second involves positing from an undetermined concept its possible determinations, for instance, in discovering disjunctive existential deductions.

The final derived capacity mentioned by Crusius is the capacity of making deductions. He lists this capacity only for the sake of completionism, but says it will be investigated in more detail later. He does remark that this capacity requires especially sharpness of internal sensing and attention. Since these are so difficult, Crusius remarks, people often make only easy deductions or even no deductions at all.

Having gone through this list of cognitive capacities, Crusius notes that external sensing, memory and ingenuity and imagination are called lower capacities of understanding, while higher capacities include internal sensing, judgement, capacity of developing ideas and capacity of making deductions. The reason for the division is, he says, that we share the lower capacities with irrational animals, while higher capacities belong only to rational entities. Whether lower or higher, all these various capacities, Crusius thinks, can have only three effects: concepts, propositions and deductions. Furthermore, all capacities of understanding can be cultivated, Crusius explains. This cultivation can be material, where we find more truths to know and use them more time, or it can be formal cultivation, where we ponder truths with more thoroughness and sharpness.

The capacities of understanding, Crusius continues, are by their nature earlier than capacities of will. Still, he admits, experience shows us that drives of will affect these capacities: we can direct our sense organs to objects we desire, we can choose to retain a current representation in our judgement etc. This means, firstly, that the state of understanding can be evaluated morally. Secondly, it means, Crusius notes, that effects of understanding can be divided into pure or unmixed, which are not affected by the activity of will, and mixed, which are so affected. Pure effects include, he thinks, sensing, retaining ideas in memory, distinguishing, at least insofar as it consists only in being aware of certain distinctions present in concepts, propositions or deductions, and free play of imagination, where we imagine now this, then that concept. Mixed effects, on other hand, include propositions and deductions, since they both require keeping attention willfully on relations of ideas, and also purposeful observing and reflecting.

Crusius notes that when we become accustomed to judging – that is, doing abstraction – our memory and ingenuity appear to weaken. This occurs, because we are habituated to start analysing new ideas, which makes it more difficult to retain this idea in our minds for a while, for the sake of memorising it or finding ingenious connections involving it. This is why adults seem not to have as good a memory as youngsters, Crusius explains, although the truth is that adults just use memory differently, memorising more easily ideas known through judgement. When reaching old age, he continues, the body starts to hinder our internal sensing, through the stiffening of nerve fluids, which makes it harder to recollect what lies in our memory to gain what truly lies in our memory. Just like memory, Crusius thinks, a free play of ingenuity appears to weaken with years, if one is accustomed to stifle its wilder suggestions, but practical and political ingenuity can still increase.

Crusius, Christian August: Road to certainty and reliability – Truth and logic

Crusius finally begins the proper study of logic, after the introductory chapters, from the theoretical part, studying powers and activities of understanding (Verstand) that make the knowledge of truth possible. By truth he refers to the correspondence of thoughts with their objects, or to put it more precisely, such a relation between an understanding that thinks and the object it thinks, so that if the former thinks that the something about the object is, is not, is possible or impossible, this something respectively is, is not, is possible or is impossible also independent of this thought. Crusius emphasises that in this definition one should not speak of the object being something independently of the understanding, since the definition should apply also in cases where the object handled is understanding itself.

Crusius notes that truth must be distinguished from both error and ignorance, where error means a lack of correspondence between thought and its object, while ignorance means a lack of any thought about a topic. In other words, we cannot speak of truth if there is no thought that has ideally exactly that which object has really. Crusius underlines that we are speaking here only of truth in its logical meaning, and in addition, there is also a notion of truth in moral or ethical sense, that is, truthfulness, which means correspondence of a state of mind with the intended meaning of external signs that are used for communicating this state of mind. Finally, Crusius also points out that sometimes we speak simply of truth, when we actually mean some true proposition.

Crusius notes that when an object is compared to an understanding, this understanding can be either a possible understanding or an actual understanding that has some knowledge of the object. In the former case, he clarifies, we are speaking of objective or metaphysical truth, which means thus truth or possibility of an object itself, insofar as it is regarded as something that could be known by any understanding, while the latter is then subjective or logical truth, which means truth in an actually existing understanding or such a relation between a representation and its object, where the representation and the object correspond and thus some truth is known. Furthermore, Crusius notes, all objective truth is subjective in relation to divine understanding.

In human understanding, Crusius continues, all subjective truth is generated by the impossibility to think opposite of what one is conscious of, where the impossibility can happen in all cases or only in the current conditions. He notes that our first thoughts are always sensations, while other thoughts are then abstracted from sensations, so that we become thus conscious of relations between our thoughts or propositions and can attend to them. Furthermore, Crusius says, when we attend to what we can and cannot think, we generate a very special kind of propositions or rules indicating awareness of deductive relations: if certain propositions are connected in certain manner through the ideas they contain, we are bound to take one as true, if we take the other as true. With such rules, we receive a capacity to make deductions with such rules. Now, Crusius argues, since we know the truth of every proposition from the falsity of its opposite, all knowledge of truth in human understanding happens through deduction, although we are usually not aware of these deductions, because they happen so easily.

On the basis of the previous considerations, Crusius states that subjective knowledge of truth in human understanding is dependent on the capacities of sensation, abstraction and deduction. According to him, these capacities are physical, hence, we can abstract physical laws from their use. In a similar vein, since these capacities are under the control of our free will, the laws of free will can also be abstracted from their use. Thus, Crusius concludes, the human understanding can find truths concerning the whole created world (both the physical bodies and the free will), if it just follows its own nature.

Conclusion that Crusius thinks he has proven is that human understanding works just fine by its own nature, even without any further education. Then again, he at once admits, errors are in this case possible, because our representations of the rules of deduction are obscure. Logic is thus required to make understanding more capable of knowing truth. In its abstract sense, Crusius explains, logic is a science that represents distinctly and exactly the effects and laws of understanding and thus shows its correct use. Logic has also, he adds, a concrete sense, according to which it is a capacity of a subject to know fundamentally the effects and the laws of understanding and its correct use.

Crusius considers the capacity of our understanding to work and thus to know truth without logical education and calls it natural logic, which means thus an inherent feeling of true and false that generates a capacity to evaluate grounds for and against something. A person with good understanding can thus recognise through this natural feeling, if some suggested laws and rules of understanding are untrue, which Crusius takes as a justification that incorrectness of suggested logical laws can be shown also a posteriori from experience, just like in arithmetics. Yet, he adds, there are more differences of opinion in logic than in arithmetics, since reflection on kinds of abstraction and on grounds of truth is more difficult than thinking about more concrete topics. This difficulty makes humans ignore the investigation of their understanding and thus rely too much on their natural logical capacity, which has a tendency to error. The wilful ignorance is furthered, according to Crusius, because treatises of logic seem to be so far removed from the use of understanding in practical life.

Logic teaches the kinds of abstraction and methods of knowledge, thus, Crusius thinks, it is the only means to make cognition sharp. He even calls logic the soul of philosophy and scholarship, because it makes them correct and distinct. Because of logic, he underlines, knowledge is fruitful, and logic gives understanding the ability to know truth and evaluate judgements, hence, it strengthens our capacity to study. In effect, Crusius concludes, logic is the subjective foundational science, just like metaphysics is the objective foundational science.

Crusius identifies two weaknesses in natural logic, which the proper logic can fix. Firstly, he says, when we are dealing with complex topics, natural logic is not enough for distinguishing true from false and for arranging our studies in a suitable order. In other words, he explains further, when we use natural logic for dealing with a complex topic, we might find material for justifications or grounds, but we still cannot give them the proper form, that is, place them in such relations that would make them justifications of something. The result would then be, Crusius insists, that we may end up suggesting many grounds or justifications that in their current state do not justify anything. He thinks that this is especially true with probable proofs, where recognising true and false is more difficult. The conclusion of Crusius about the first weakness is that the natural logic is applicable only, on the one hand, in common tasks of human life, where object is characterised with sensuous properties, and on the other hand, in distinguishing moral good and bad, because our understanding of good and bad is supported by conscience and a feeling of guilt. The second weakness Crusius finds in natural logic is that the lack of proper logic often leads to errors and even outright scepticism.

Crusius goes on to divide the parts of logic. First of these parts is, according to him, the theoretical part that handles grounds that make the knowledge possible in the human understanding, and in addition, must also consider the powers of human understanding and its effects or concepts, propositions and deductions. The study of the powers of human understanding Crusius calls noology, necessary truths of which belong also to metaphysics. Crusius also emphasises that noology needs to investigate only what lies in the soul, together with the general features of the dependence of certain effects of understanding from the body. Then again, external conditions of sensations in bodies belong to the study of nature.

The other or practical part of logic, Crusius says, explains how the powers and effects of understanding should be used for the purpose of truth. It also deals with the illnesses of these powers, the experience as a modification of the power of sensation, use of concepts in divisions and definitions, use of propositions in judgements, and use of deductions in proving, recognition of seeming proofs and decision over colliding proofs. All the effects in unison, Crusius adds, are handled by the study of method and also in some special topics, such as interpretations, special kinds of probability and disputation.