In a previous post, I started (re)introducing some of the basics of Aristotle, focusing on his view of nature (phusis) and thinghood (ousia), showing how the cosmos can be understood as an individual thing that is in motion—material swinging from form to form. In other natural bodies, the movement of material to form is characterized by growth, self-nourishment, and wasting away. Aristotle defines such bodies as living bodies (On the Soul [Joe Sachs, trans.] 412a12). Aristotle investigates the nature and thinghood of living bodies by way of an investigation on the soul (psyche), “since the soul is in some way the governing source of living things” (402a6). Like his investigation into nature, the opening of the investigation concerning the soul responds to the thought of Aristotle’s predecessors, which for the most part supposes the soul to be an elemental body or composed of elemental bodies (403b20).
In the second book of his investigation concerning the soul, Aristotle offers his definition of the soul, which follows from his understanding of nature and natural bodies. Just as natural bodies have thinghood as composites of material and form, so too do living natural bodies (412a15). The body (soma) is what the independent thing is called that underlies the growth and decay it endures. The body, then, is underlying material having potential for life. The body has no further thing underlying it. Therefore, the soul (psyche)—the cause of life in the body—is not a material body, but is the being-at-work and form of a material body (412a20). Like the being-at-work of the form of natural bodies, the being-at-work of the soul is the being-at-work-staying-itself of the living body. The soul, then, is what a body keeps on being in order to be at all (to ti en einai), and this is the thinghood of the body as it is revealed in speech (ousia he kata ton logon) (412b10).
The living, or ensouled, body is distinguished from non-living bodies by the presence of one or more of the following potencies of the soul: intellect, perception, movement with regard to place, and nutrition (414a30). A plant has share in the nutritive (threptike) part of the soul, which manages the work of growth and nutrition. Growing and living are the being-at-work-staying-itself that is the thinghood of the plant. The soul of the plant is the form that actively maintains itself.
Animals also share in this nutritive potency of the soul. However, animals also possess the perceptive (aisthetike) potency of the soul, and some animals are also capable of moving themselves with respect to place. Furthermore, some animals have the capacity to reason and think things through (415a). The way in which an animal’s senses are directed and attuned to the sensible world is a kind of ratio or rationality (426b5). However, this does not mean that animal thinking is identical with the kind of thinking proper to humans.
Aristotle distinguishes two types of thinking: imagining and conceiving (opining or knowing) something to be the case (427b30). Imagination differs from perception in that a sensible thing need not be present to the senses for it to be imagined, although it must have some connection to sensibility. What appears to the imagination is sometimes true, but not in the way that knowledge is true; and it is sometimes false, but not in the way an opinion or belief is false (428a). Opinion and knowledge only belong to the animal capable of speech, the human—the rational animal (zoion logon echon).
The part of the soul that conceives of things—the intellect (nous)—is completely receptive of the forms of those things it apprehends (429a15). This receptiveness of form is present in greater degrees from formed material to the different potencies of the soul. Just as the nutritive, motile, and perceptive potencies are open to the presence of nutritious, distant, and perceptible things in their formed material, so the intellect is open to the presence of intelligible things.
Whereas the percept and the perceiver are not the same during the act of perception (since the percept is sensed in its material aspect, which is apart from the perceiver), the intelligible is one with the intellect in the being-at-work of contemplation. Being-at-work-staying-itself, thinking is the same as and what is thought (Metaphysics 1074b35). Free of dependency on sensibility, the being-at-work-staying-itself of intellect is the original cause of all motion and being. Aristotle calls this original cause God (1072b).
The contemplative intellect is that form toward and from which all matter stretches. Potent material bodies are always reaching for contemplative intellect, which is always at-work, staying itself, untouched, attracting material toward itself. Natural bodies have their thinghood ultimately in the eternal being-at-work-staying-itself of contemplative intellect. These bodies keep being themselves by essentially swinging, stretching from and toward nous—the psyche of the cosmos.