Just like Wolff, Baumgarten divides psychology into two parts, empirical and rational. Yet, just like with the previous parts of his metaphysics, the interesting thing is to see where Baumgarten deviates from Wolff's examples. Like in many previous cases, the first obvious change is the lack of full proofs in Baumgarten's text. The existence of soul is almost just assumed from the fact of our self-consciousness – there must be something, which can be conscious of itself. Then, by just noticing that this soul must be that which underlies all states of being conscious of something – that is, of representing something – Baumgarten at once concludes that the soul must be a force or activity of representing things.
Just like with Wolff, in Baumgarten's psychology my body is not really mine at all, but just the material body that I happen to represent most often. Still, Baumgarten at least makes it clear that representations of a human soul are somehow directed by the position of its body – if my body would now be in Lincolnshire, I would have very different representations of the world around me.
Baumgarten assumes from Wolffian philosophy the hierarchy of different levels of clarity and distinctness of representations. A striking novelty is Baumgarten's idea that there are actually two different scales, according to which the clarity of a representations could be evaluated. Firstly, there is the intensive clarity, which measures how well we can distinguish a thing through that representation – this is the basis of what in Wolffian philosophy distinguished clear and eventually distinct representations. Secondly, there is extensive clarity, which measures how many individual characteristics of a thing are represented – in effect, it tells how vividly we experience some object. Extensive clarity is something that even non-distinct representations might have in abundance, and for evaluating such vividness Baumgarten suggests a completely new science, which he calls aesthetics. In effect, such aesthetics would include what we understand by the term, but it would in general be a science investigating all non-distinct or sensitive cognition.
Baumgarten's account of the sensitive cognition is somewhat more scholastic than Wolff's - while Wolff is often satisfied with indicating that several cognitive skills are somehow interrelated, Baumgarten tries to make clear divisions and thus presents far more individual faculties. Both philosophers have fairly similar stories to tell about the basis of all cognition, that is, sensation, which for Baumgarten refers to a cognition of the present state of the soul and the body (and thus mediately of the world), in which levels of intensive and extensive clarity are different.
Baumgarten's account of imagination shows already the scholastic tendency I mentioned. With Wolff, imagination was a name for a complex of interrelated skills, such as memory and invention, which all rely on our ability to represent things which are not present to us. With Baumgarten, on the other hand, imagination is merely this ability to represent things, which are not present us – and in fact, it is precisely an ability to represent past states of soul, body and world. Memory, or the ability to recognise an imagined representation as past, is already a distinct ability for Baumgarten. In addition to memory, Baumgarten also distinguishes such faculties as perspicacity (ability to perceive identities and diversities of things – note that this happens already at a level, in which we don't really have distinct thoughts) and innovation (ability to combine imaginations to form new representations). Especially the faculty of innovation comes with an interesting twist. Both Wolff and Baumgarten admit that even imaginations represent individual things, but whereas Wolff included innovation as one type of imagination and thus implied that even such fictional combinations of phantasms, like centaurs, are individuals, Baumgarten could conceivably state that such fictive innovations are no individuals, since innovation as a faculty differs from imagination.
In Baumgarten, our capacity to represent past things is based on the fact that all past and present things form a causal nexus. Because a similar nexus connects present to future states, Baumgarten concludes that we must have a faculty of representing future things and events, although this appears to be more obscure than representing past things. Just like Baumgarten distinguished sharply between imagination as representing past and memory as recognising something as past, he also points out a further faculty for recognising some representation as being of a future event – this is the faculty on which prophesising is based. A more mundane example of such a ”vision of future" Baumgarten presents in connection with another faculty or judgement, which means for Baumgarten representing or perceiving how perfect or imperfect something is (all of this happens still at the level of non-distinct cognition). If such a judgement is turned on future events, it can be used in practice for deciding how to act.
Just like with Wolff, intellect or understanding is not a completely distinct faculty separate from sensation, but more of a higher level of human mind, born out of sensations through attention, reflection and comparison. In difference to Wolff, Baumgarten points out that intellect forms only a one possible way to improve our cognition. Intellect or understanding is generated by purifying our sensations, that is, through clarifying our ideas, but it is also possible to make our representations more vivid – this makes our mind more in tune with what is beautiful.
Following Wolff, Baumgarten explains human feelings of pleasure and pain through the notion of perfection – perceiving something as perfect makes us feel it pleasurable, while perceiving something as imperfect makes us feel pain (of course, it is also possible that an object is not regarded as either). Expectations of pleasure and pain make our soul strive for something and thus act like motives.
Baumgarten is quite clear that our soul requires such a motive to do anything at all – if we are not forced to do anything, we will follow our own motives. Such motives could be generated either by mere sensations and other indistinct representations – then they are mere impulses – while conscious motives are caused always by distinct representations. Here a real freedom means then action instigated by such conscious motives.
The final topic of Baumgarten's empirical psychology is the interaction between soul and its body. Baumgarten says that on basis of mere psychology we cannot say which is better, the idea of a true causal interaction or the idea of a pre-established harmony. Yet, as we already know, his idea of the perfect possible world points towards the Leibnizian idea.
So much for Baumgarten's empirical psychology, next we shall see what he has to say about rational psychology.