The worth of Baumgarten in developing aesthetics is generally recognised, but the case is somewhat different with his metaphysics. True, this part of his philosophy has also found its readers, especially as people have wanted to see, why Kant used it in his own lectures of metaphysics. Then again, one still finds articles, in which Baumgarten's metaphysics is seen as little more than a continuation of Wolff's metaphysics and all the innovations of former are just implications of the latter – a view which does no justice to either of the philosophers.
When one just glances the contents of Baumgarten's Metaphysica, one might think that the association with Wolff's metaphysics is justified, as we find the book divided into four parts: ontology, cosmology, psychology and theology. Of course, this is just an external classification and one could argue that even Kant and Hegel still retained it at least partially, without being Wolffians. To make a more reliable judgement on the relation of Wolff and Baumgarten, we must then go into the details of latter's metaphysics.
Let us begin with ontology. Again, on superficial level, Baumgarten has borrowed his division of topics from Wolff. Baumgarten takes ontology to be a science of most general predicates of things and then suggests that such predicates are either internal (i.e. monadic) predicates or relative, while internal predicates are either universal (true of everything) or disjunctive (combination of predicates, exactly one of which must be predicated of everything). Indeed, Wolff also described first several general features of things, then the most general genera of things and finally general types of relations. Yet, a subtle difference can be seen already in these divisions, since many of the topics described by Wolff in the first division belong to second division in Baumgarten's ontology, while with Wolff, the second division contained only the oppositions of simple/complex and finite/infinite.
An even more interesting difference lies in Baumgarten's discussion of Wolff's highest principles of ontology. It appears that for Baumgarten it is concepts that are far more important than principles, and e.g. principle of non-contradiction is investigated in a chapter dedicated to possibility. Even more distant from Wolff's methodology is the lack of justification of these principles. Wolff's strategy in both German metaphysics and Latin ontology was to make an inductive move from individual cases, in which contradictions were denied – from a single case involving our own existence (in German metaphysics) or from our general tendency to deny contradictions (in Latin ontology). Baumgarten straightaway defines combination of predicate with its contradictory as impossible and uses that definition as a justification to conclude that no possible subject cannot have contradictory predicates.
Of course, this might just be an expositional feature of Baumgarten's text. The terse style of the book belies that it is meant to be used as a text book, and it might well be that Baumgarten is just describing the general features of his ontology, instead of arguing for its validity. This might be suggested by the fact that Baumgarten makes at this stage a rare reference forward – the principles are justified by the conclusions we can draw from them.
In this rather terse beginning, Baumgarten makes a rather strange remark: ”A + –A = 0”. Later on Kant would speak against such statements, which appear to conflate purely formal contradictions with conflicts of opposed forces – and indeed, we have seen Hoffmann already make similar observations. Yet, it is perhaps not so much that Baumgarten would have conflated these two notions, but that he never had a notion of mere formal contradiction – this is something one could have seen already with Wolff, who thought that wooden metal was an example of contradiction, although logically speaking there's nothing contradictory in the notion. It might well be that we should take the equation of Baumgarten quite seriously – A and non-A are like two forces or tendencies inherent in all things and an attempt to actualise them both in the same subject can end up only with destruction of the subject.
It is important to take this ontological nature of Baumgarten's and Wolff's notion of contradiction seriously, because both philosophers used contradiction as a way to define nothingness or impossibility, and so in consequence the opposite, that is, the notion of something or possibility. In other words, the hidden ontological implication is that there are some primary forces and any combination of them is a possibility, just as long as these combinations are not mere nullities, that is, ontologically barren points of no force or activity.
This hidden view of primary forces is probably behind Baumgarten's next move, in which he, following Wolff's example, tries to prove principle of sufficient reason. Just like Wolff before him, Baumgarten defines reason or ratio of X in epistemic terms as something, through which one is able to know X. To possibly have such a reason or to possibly be such a reason are enough to make something rational, while irrational, that is, something that cannot be connected with any other possible state as having a reason or being a reason, is nothing more than an impossibility – the hidden presupposition is clearly that we cannot have any isolated fact or event, but all possible states are connected to other possible states.
With this hidden presupposition, it is easy for Baumgarten to show that the principle of sufficient reason is true. If these presuppositions are assumed, something not having something else as a reason could mean only that it has ”nothing” or a state of nullity as its reason, because mere being without no reason would be just incomprehensible. Yet, this alternative doesn't work either, since a state of nullity is in Baumgarten's ontology a synonym for impossibility – the only alternative left, then, is that this something has as its reason some non-null state or something else. Furthermore, similar reasoning works also for the other direction, that is, Baumgarten can conclude that all possible things are reason for something else.
So far, then, Baumgarten has mostly just augmented Wolff's presentation at some points and made its presuppositions even more glaring. Of course, while Wolff could always rely on experience, Baumgarten's terse method of presentation makes these presuppositions truly stand out. Next time, we shall see him moving away from Wolff's philosophy in an even more radical fashion.