The rest of Baumgarten's ontology is perhaps not as original as the earlier sections, but it is at least interesting, because Baumgarten rearranges topics and includes in general relational predicates some issues that Wolff did not consider under relations. The first of these topics is identity and the related notions of diversity and similarity. Here we find Baumgarten, for instance, endorsing the Leibnizian principle of the identity of indiscirnibles: two different things cannot be completely similar.
Space and time or simultaneity and succession are also dealt by Baumgarten in the chapter on relations. Although Wolff had also endorsed the idea that space and time are nothing but relations, Baumgarten is making this notion even more explicit by this simple choice of how to present the topic.
Just like with Wolff, the central relational notion in Baumgarten's ontology is obviously causality. Cause is for Baumgarten, just like it was for Wolff, a more special modification of ground or reason. For Baumgarten, cause is specifically a ground for the existence of something. Just like Wolff before him, Baumgarten defines several notions important to causal considerations – some causes might coordinate with other causes in producing some effect, while others may be called more proximate, when compared with more immediate causes of something.
The most important type of cause for Baumgarten is probably the efficient cause, which has actively produced some reality or positive characteristics in something else (Baumgarten also invents the notion of deficient cause for those actions, which produce some negative characteristics). A number of other causal notions can then be defined in terms of whether they help an efficient cause to do something or whether they hinder it.
In addition to efficient cause, Baumgarten does also, just like Wolff before him, consider the other three Aristotelian causes: form, matter and final cause. This part of Baumgarten's ontology seems rather quaint, like a remnant of a past long gone.
The final relation Baumgarten considers is that between signs and what the signs express. Although Wolff did briefly consider this topic, Baumgarten somewhat expands Wolff's writing. For instance, he considers several sciences, in which one should either make up more signs (heuristics) or help us recognise past signs (mnemonics), and also tries to explain the genesis of human language.
So much for Baumgarten's ontology. Next time I'll look at his cosmology