Crusius concludes his study of ontology with the notions of perfection and goodness. He is especially eager to reject the Wolffian notion of perfection as a harmonious unification of a manifold. Instead, he suggests, by perfection we can, firstly, mean the sum of positive reality ascribed to a thing. He clarifies the definition by noting that this positive reality refers to the causal powers of the thing or effects that become possible or actual through it. Secondly, Crusius adds, perfection can also mean an individual aspect of the thing contributing to this sum of positive reality.
Just like causal power, Crusius notes, perfection can also be either infinite or finite, and in case of finite perfections, there are always higher and lower levels of perfection. In a sense, any perfection beyond the infinite is lacking something, but even finite things can be perfect in their kind, Crusius assures. Furthermore, he adds, perfection can be either essential, that is, presupposed in the essence of a thing, or contingent, that is, aspects increasing the perfection of the thing, but not presupposed by its essence. It is the essential perfections that make a thing perfect in its kind, while contingent perfections by themselves cannot do this - a mirror that reflects poorly is an imperfect mirror, no matter how costly frames it has.
How then to decide what belongs to an essence of a thing, and consequently, to its essential perfection? Crusius says it all comes down to purposes they are made for. In case of things generated by natural causes, he notes, we might not be able to say what the original purpose of the creator was for them. In this case, we can try to determine their purpose and thus their perfection from what we have experienced of them and their parts.
Just like with many concepts earlier, Crusius notes that perfection can be either ideal or real. By ideal perfection he means a property of a thing, by which understanding can perceive more truth, order and relations in it. He especially considers the notion of order, that is, an arrangement of things in a manner that appears to have been done according to an idea or a model. Depending on the model, order can be better or worse, but generally, Crusius says, it is better the more diverse things are arranged harmoniously. Order can be based on similarity, but not necessarily, for instance, letters of very different sort are ordered in words.
Real perfection, on the other hand, makes possible something else than mere knowledge of order. In other words, real perfection is for Crusius either an active cause generating something actual or an existential ground making something possible or determining something.
In addition to the division of real and ideal perfections, Crusius also mentions a division into external and internal perfection. Here, external perfection means something we can sense, while an internal perfection is to be found in an inner essence of a thing. Interestingly, Crusius notes that a thing that is externally and internally perfect is by definition beautiful.
Crusius lists various signs that something can be taken as perfection. For instance, any part of an essence can be taken as perfection, thus, understanding is a perfection. Furthermore, anything serving purposeful sustainment of the essence is perfection, like health, as is anything that makes a thing capable of securing more of its purposes or surer or easier to do so, such as prudence or science. Perfections include also anything that forms a main purpose of a thing or is a required means for it, such as virtue and care for one’s well being. Finally, the class of perfection contains anything that is an unavoidable consequence of a perfection, such as despising unfounded gossip, and also anything showing perfection, like art.
Not all that seems perfect truly is so and vice versa, Crusius clarifies. For instance, looking at mere ideal and external perfections, such as beautiful book covers, might confuse us to think that the thing in its essence is also perfect, when it is not. On the other hand, what is imperfect from a partial perspective could be perfect from a larger perspective, for instance, if the main purpose of the thing requires such a partial imperfection. Thus, while lack of light is usually an imperfection in a room, it is not, if the room in question is cellar.
Crusius ponders the question whether perfection belongs to things necessarily. Since the infinite substance has only necessary properties, its perfection should also be clearly necessary. Crusius also insists that all the things dependent only on the choice of the infinite substance must be perfect in their own kind. This still leaves the cases where free choices of finite substances are involved, and it is this freedom that brings about the possibility of imperfection.
From perfection Crusius turns to the notions of purpose - what a person wants - and means - what a person uses to achieve a purpose. A purpose is good, Crusius says, if it agrees with the essential volitions of the person, while a means is good, if it agrees with the purpose it should serve. The latter notion of agreement, particularly, has many different subtypes: a true means really helps to obtain the purpose, a certain means generates it always or regularly, a sufficient means can do it without any other help and a strong means generates the purpose exceptionally well or for a long period of time or for many persons.
Goodness is then for Crusius a concept necessarily linked with the concept of a purpose, but different notions of goodness arise depending on whose will the purpose is supposed to depend on. Thus, a finite thing is metaphysically good, if it corresponds to a purpose set by God on the natural chains of events, and physically good, if it corresponds to volition of finite persons. These two types of goodness can be defined also in terms of perfection, Crusius adds, because e.g. a thing is physically good if it makes some person more perfect. Still, all varieties of goodness cannot be reduced to perfection, Crusius notes and refers especially to a notion of moral goodness, which is especially a property of free persons and their actions: the condition of a person is morally good, if it agrees with the law willed by the infinite substance.
Finite things can be good, but the infinite substance must be good, Crusius emphasises. Indeed, the infinite substance is good in many ways. It is essentially good, because it is the only possible source of goodness for finite things. Then again, it is also good as showing kindness toward finite things. In addition, the infinite substance is also good also without any regard to finite things, because it is constantly what it can be.
Just like goodness, evil comes also in many varieties, Crusius says. A thing can be physically evil, if it is in conflict with desires of a finite person. Secondly, a state of a person can be morally evil, if it contradicts the divine law. Finally, a thing can be metaphysically evil, if it is not fit for achieving those effects, which should be possible through it according to divine purposes. Crusius notes that things depending on mere natural chain of events cannot be metaphysically evil. Thus, metaphysical evil always requires the intrusion of a free choice and is thus a species of moral evil.
