An important division of things in Crusius’ ontology we didn’t consider last time is that of incomplete things. An incomplete thing, Crusius explains, is such that, if it should exist, it must be connected to some other thing. A good example would be a location of a thing in relation to other things: clearly, if a location exists, there must be a thing which is located in this manner.
In addition to such external circumstances (umstände) like location, examples of incomplete things, Crusius says, are provided by the relation of subsistence. Crusius has inherited this notion from tradition, but as it is simple and cannot therefore be really defined, it is difficult to understand what is meant by something subsisting in something else. Crusius does provide illustrations of the relation, examples being relation of a certain shape to a piece of matter, understanding to a soul and even foot to a human being. Here, that which subsists Crusius calls property (rather confusingly, because properties were also parts of essence) or predicamental accident, while that where something subsists is called a subject.
In a rather inconsistent manner, Crusius sometimes speaks as if subjects were the stable element in the relation, although in many other places he underlines that subject and its accidents are incomplete and only their combination - essence or substance - is the true complete thing, just like matter and shape or form are just two aspects of a shaped material object, like a book.
Subsistence relation forms chains, with subjects subsisting in further subjects, Crusius explains, just like science subsists in understanding and understanding in soul. Crusius suggests that these chains cannot go on indefinitely, but there must be some absolute subjects, which do not subsist in anything else. Well, to make the matters more difficult, Crusius suggests then that even absolute subjects can subsist in a further subject, just not like a property subsists in a subject.
In some cases a subject is necessarily connected to a certain property, in other cases not, Crusius says. Examples of the latter would be, on the one hand, red colour of a house, on the other hand, person’s ability to speak Latin. These two examples are very different in nature. Someone might not have an ability to speak Latin, without having an ability to speak anything else, Crusius notes. Then again, if the house is not red, it still has some colour. Colour is what Crusius calls a house’s possible way of existence or its determination.
A thing with some determinations missing cannot really exist, Crusius explains, although we can think of such an indeterminate thing as a subject of further determinations. Just like Wolffians, Crusius defines an individual thing as being fully determinate. With all its determinations, an individual is differentiated from all other individuals, while abstractions from individuals can exist only in several individuals.
Crusius also divides properties into positive and negative properties. This division is linked with the notion of determinations in the sense that when we think of a negative property, we then implicitly think of some positive property, but only indeterminately (what is not yellow is still coloured somehow). Crusius divides negative properties further into merely negative and privative determinations (think how it is different to say that coal is not alive and that JFK is not alive). Similarly, he divides positive properties into absolute properties and relations.
To further explain what makes property positive, Crusius states that all of them are forces, that is, they make other things possible or even actual by themselves or with the help of something else. This leads Crusius to deal with the notion of causality. Epistemically, he says, causality is justified by it being impossible to think of something being generated without being an effect of some cause. The corresponding principle of sufficient reason, Crusius insists, cannot be deduced from the principle of non-contradiction, because there is no contradiction when things are different at different times. Furthermore, he continues, causality is a concept we cannot really define - it is so simple that we can only show how this concept can be abstracted from our experience by noting e.g. how our experiences of fire and warmth are linked to one another, without one being part or determination of the other.
Crusius also links causality to what he calls a principle of contingency: what can be thought as not existing must have really not existed at some point in time. The idea behind this principle is that if we then find such a contingent thing existing at some point, it must have been actualised by some force.
Forces or causes are for Crusius one type of ground. There are also other types of ground, he continues. For instance, because a triangle has sides of certain lengths, it must also have angles of certain sizes. Here, the lengths of the sides are a ground for the sizes of the angles, although the sizes clearly do not cause the angles to be of a certain size. Crusius calls such an existential ground.
Both causal ground and existential ground fall under what Crusius calls a real ground: the idea is that in these cases what is grounded is something outside thought. Ideal ground, on the other hand, Crusius defines as something generating knowledge and conviction of something. He also divides ideal grounds into a posteriori and a priori grounds. In an a posteriori ground the concept of what we are about to prove is already present, while the ground at most reveals that this something exists. A priori ground, on the other hand, generates also an idea of what we are grounding.
Returning back from this detour to an essence and its properties, we find Crusius dealing with what he calls the fundamental essence of a thing and attributes, which are constant properties, grounded in the very fundamental essence of the thing. Some of these attributes are necessary or essential: the existence of these attributes is inevitable, once the fundamental essence behind them is supposed to exist. The other type of attribute Crusius deals with is natural attribute or property, which is present in things of certain type usually, but could be absent in extraordinary cases, although the fundamental essence of the thing would remain the same. He notes also that some attributes are based only on the fundamental essence of the thing, while others are based also on external, but constant causes.
Crucius notes also that some attributes mark a real existence of some condition, while others mark only a capacity for something, activated by external causes, contingent activity of the fundamental essence or both. Such activation of capacities makes then possible the change of contingent properties or modi of a thing. By a modus Crusius refers to properties that make an indeterminate thing more determinate by adding to constant properties something variable, which could be replaced by another modus.
Crusius also considers the distinction between a necessary and a contingent fundamental essence. In a necessary fundamental essence properties constituting the fundamental essence of a thing cannot be separated from one another without supposing some contradiction. In this case, also the attributes flowing from the fundamental essence of the thing must be necessary, and indeed, the only thing that can be up to chance is whether the thing itself exists at all. Contingent fundamental essence, on the other hand, refers to a fundamental essence, where some of the constituent properties can be removed without any contradiction. Crusius notes that all finite substances have in this sense a contingent fundamental essence.
These notions lead Crusius to consider a more general question: what does it mean when we consider whether presupposition of a certain determinate essence contradicts a presence or absence of a certain property? His answer is that all this question can reveal is that presence or absence of a property is necessary for a certain concept. Thus, we cannot add a fourth angle to a triangle, without making it not agree with the concept of a triangle. This does not mean that the properties of the thing would be necessary outside our concepts (e.g. a triangle could be changed into a quadrangle). Such a substantial necessity of properties is present only in the cases, Crusius explains, where removal of this necessary property would make the thing incapable of even existing.
