One of the most perplexing parts of Wolff's ontology is his notion of determination – something that can be affirmed of a thing. Are these determinations subjective or objective? The definitions appear to support the former reading, but the way Wolff actually uses these determinations to define possible things seems to support the latter reading. Furthermore, it is unclear whether these determinations should be universals or abstract particulars, i.e. tropes. The most faithful reading would perhaps be to deny that determinations are either, since both universals and particulars are defined through the determinations. Still, they seem more like universals, since unlike with particulars, they could be joined with other determinations.
Whatever these determinations are, Baumgarten accepts the notion, although he defines it in a somewhat different manner. Something is determinate, Baumgarten says, when it has been posited as A or not-A. The term ”posited” might seem rather strange, and indeed it is so – it is not quite clear whether Baumgarten wants to say that something is affirmed as A or not-A or whether it merely is A or not-A or perhaps both. Still, what is posited in something determinate is then a determination. If the posited determination is positive, it is a reality, otherwise it is negation. Since it seems objectively quite hard to say, which predicates should be called positive and which negative, the division appears rather arbitrary – yet, it should not be just subjective, since Baumgarten clearly distinguishes cases, in which e.g. seemingly positive determinations are actually negative.
Baumgarten's manner of distinguishing various determinations appears familiar from Wolffian ontology. Determinations can belong to a thing either as the thing is in itself – then it a question of absolute or internal determinations – or then as the thing is with respect to other thing – then it is a question of relations or external determinations. The internal determinations of a thing are either ground for all other internal determinations – then they are essentials, sum of which forms an essence – while other internal determinations are affections. Affections are then either wholly grounded in essentials – then they are attributes – or not – then they are modes.
Now, Baumgarten notes that a possible thing must be something that can be regarded in itself or without any relations to other things – that is, a possibility must be something with at least a minimal identity, by which to regonise it. This is quite a remarkable suggestion that is not included, at least explicitly, in Wolff's ontology. The important consequence of this suggestion, on the other hand, is something that we find from Wolff. If something is possible, it must have some internal determinations, because without them we could not speak about anything, and since these determinations must be grounded on something, the possible thing must have an essence. In other words, all possible things should have an essence.
Clearly a thing with some essence could also be merely possible, since e.g. centaurs do have an essence without existing – this is something Wolff agrees upon. A natural question then is what makes something possible into something actual or existent. Wolff's answer is, briefly put, that it ultimately has something to do with God's decision to create just this particular world, but that it also lies beyond complete understanding of human beings. In this matter, Baumgarten deviates considerably from Wolffian example, although almost no one has recognised it.
Baumgarten almost equates the essence of a possible thing with its possibility. What about the rest of the internal determinations of a thing, especially its modes, which are not determined by mere essence? Simple, they are part of existence. More determinately, it is the sum of all the internal determinations that supposedly forms the existence of a thing. In other words, while all actual things clearly cannot have any more determinations and are in that sense complete, all possible things should also be in some measure incomplete or indeterminate.
Baumgarten's theory is remarkably curious, although even more curious is that Wolff has been considered to endorse this theory, at least implicitly. True, Wolff says that actual things are completely determinate, but he never affirms that all completely determinate things would be actual. In fact, Wolff identifies complete determination with another ontological notion, or individuality. As Wolff, for instance, accepts the existence of haecceitas, which might be described as an analogy of essence in individuals, it seems quite unreasonable to suppose that Wolff would have thought all individuals are actual.
Baumgarten, on the other hand, makes this bold move and declares all individuals to be existent, thus denying the possibility of merely possible individuals. One explanation might be that he has been led astray by the notion of positing in his definition of determinations. True, we human beings can posit some thing to be completely determinate, only if we can experience it and thus know that it exists. Yet, this does not mean that God with his infinite capacity of thinking – something which Baumgarten himself should believe in – could not think of a completely determinate individual, which still would not exist. It is then Baumgarten who has fallen for the old trick of confusing capacities of human understanding with the capacities of divine understanding – something, of which Kant was to later accuse his rationalist predecessors.