The final task of Wolff's Latin rational psychology is to show the place of human souls in a hierarchy of what could be called mental entities – a hierarchy in which humans form neither the highest nor the lowest rang. Completely outside this hierarchy are material entities, but apparently also mere elements of material entities, which have no mental capacities and which do not represent the world in any proper sense of the word. Wolff is thus clearly distancing himself from the monadology of Leibniz, in which all monads actually perceived.
Even if Wolff does not accept elements as souls, he dos affirm that animals have mental capacities: animals have sensations and thus consciousness, they are guided by sensuous appetites and aversions and they can even imagine things that they are not perceiving. Thus, Wolff concludes, they must have souls. It it not clear how substantially Wolff wanted to understand this ascription of souls to animals, because the capacities Wolff has described as belonging to animals are all such that have bodily counterparts in Wolff's scheme. Is saying that animals have souls only another way to point out that animal bodies exhibit similar processes as bodies of truly ensouled humans or should animals truly have a simple substance that senses, imagines etc.?
Whatever the case about the supposed animal souls, Wolff says that they clearly lack some capacities inherent to humans. Animals particularly do not have the capacity for language, and because of that, they cannot think or have distinct perceptions or concepts. Thus, they also lack proper self-consciousness and cannot therefore even have free will. Wolff takes this distinction between unself-conscious animals and self-conscious humans as important enough to warrant a new concept: spirits, Wolff says, are entities capable of self-conscious intelligence and will. While it was unclear whether animal souls are simple entities, spirits undoubtedly must be.
It comes as no surprise that Wolff does not want to restrict the concept of spirit to mere humans. He notes that human spirits or souls have essentially limited intelligence and will: they do not understand world or the essence of goodness completely. This suggests then a possibility of a perfect or infinite spirit that succeeds where humans must fail. Another important concept is the notion of a necessary spirit or a spirit that cannot be created nor destroyed, but has always existed and will always exist. Although Wolff does not yet identify the two, it is clear that the roles of an infinite and a necessary spirit will be combined in the person of God.
Human spirits are then not necessary, but can be created and destroyed, although as they are simple substances, their creation does not involve combination of parts and their destruction does not involve taking them apart. Now, since it is only such material creation and destruction that we understand, creation and destruction of human spirit lies beyond our understanding. Still, we can see at least that human spirit cannot have been formed from the spirits of its parents, because two simple entities cannot be turned into a third simple entity.
Wolff goes on to speculate that even a fetus must have a soul, since it evidently can have sensations. Still, all the perceptions of the fetus must still be obscure and therefore it cannot have any consciousness nor any memory. This raises the question whether the human soul is meant to be generated along with the body or whether it might have pre-existed, say, as the soul of some animal. Whatever the case, the perceptions of the soul become more clear and more distinct, when the fetus develops into a full-grown human being. Wolff concludes that this level of distinctness and the memories gathered by the soul cannot suddenly disappear when the body dies, but human spirit must go on living in another shape.
This is as much of Wolff's rational psychology I am going to examine. Next time, it shall be a good time to return to some of the opponents of Wolffian school.