The Aristotelian Soul
Structure versus Substance
This is misleading, perhaps, but in the same way that a wax statue of Napoleon is a material substance (lump of wax) with a shape or structure (the shape of Napoleon) some physical bodies (living things) have shapes or structures which enable them to grow or take nutrition, change place by locomotion, or reason by thought. The soul, Aristotle claims, is the form matter has in virtue of which it is a living thing.
"Form", here, is not to be understood in Platonic Terms or even in the terms of shape the Napoleon wax statue example would suggest. "Capacity" comes closer to what Aristotle proposes. Thus the soul, for Aristotle, is the capacity a natural body has to engage in the activities of living things. Note that this is a much wider conception of the soul than Plato's, and it begs the question, what capacities do living things enjoy non-living things don't?
The Capacities of the Soul
Souls have various capacities that in turn define the kinds of living things having them.
- Self-nourishment
- Growth and Decay
- Sensation
- Locomotion
- Understanding
If we think of these as increasing capacities, then particular living things are differentiable by the number of capacities they enjoy.
- Inanimate objects like rocks have none of these capacities, and thus have no souls.
- Plants at most have souls with the capacities for nutrition and growth.
- Animals have souls with the capacities of plants' souls and the capacities of locomotion (movement) and sensation (perception).
- Human souls have all the capacities of plants and animals and the capacities for intellectual activity and reason (understanding).
Thus there is a continuum from the inanimate to the fully active and cognizant.
Mortality of the Soul
Because the soul of a living thing is a material substance having specific capacities, the dissolution of the material substance implies the loss of whatever it is about the substance that underwrites those capacities.