Physiology of cognitive powers in Descartes' natural philosophy

According to Descartes’ dualistic conception of the world, existing things are divided into thinking substances and extended (bodily) substances. While all cognitive processes, in the strict sense of the term, take place only within thinking substances or minds (from God down to human souls), insofar as these have particular ideas (representations), Descartes understands the only true properties of bodies to be various shapes and motions. Changes in the bodily world are thus explained in a mechanistic way, that is, as the result of collisions between moving bodies. The fact that Descartes locates all ideas, or all cognitive operations in the strict sense, within the interior of the mind or soul should not lead us to the intellectualist conclusion that the body plays no role in his theory of human cognition. Such an intellectualist reading of Descartes’ theory of knowledge—sometimes offered in cognitive science and neuroscience—overlooks the fact that Descartes conceives human nature as a union of a particular mind and a particular body. Consequently, within the mind he distinguishes between those thoughts that the human mind can form by itself (all acts of understanding) and those that it forms only insofar as it is affected by the body with which it is united. These body-dependent cognitive activities of the mind, along with their associated cognitive aspects, include sensory perception, imagination, associative memory, and corporeal attention. Since these processes are always the result of specific bodily processes, Descartes, for example, distinguishes between three grades of sensory perception: the first consists of bodily processes that act upon the mind; the second consists of sensations that the mind consequently forms; and the third consists of judgments that the intellect forms about the objects of perception. The same three-phase model should also be applied to other cognitive processes that presuppose bodily influence. These processes can only be fully understood when we distinguish and explain the various bodily mechanisms that constitute the first grade of the corresponding cognitive processes. A comprehensive explanation of Descartes’ theory of knowledge therefore requires a descent into physiology.

The problem is that studies of Descartes’ theory of these psychophysical processes have so far either focused on their purely mental aspects or on aspects concerning the nature of the relation between the human mind and body (so called substantial union), while leaving aside the question of the nature of the various bodily mechanisms underlying the corresponding cognitive processes. This absence is also evident in studies of Descartes’ physiological theory, insofar as they have directed their attention to his mechanistic explanations of motor and vegetative bodily processes, while largely neglecting the physiological aspects of cognition.

The main aim of the project is to address this double interpretative gap by distinguishing between and explaining the mechanisms that underlie particular cognitive processes.

Achieving this goal will require a turn to Descartes’ earlier works which, unlike his mature works (Meditations on First Philosophy from 1641 and the first part of Principles of Philosophy from 1644), were not devoted to the metaphysical grounding of the natural sciences through proofs of God’s existence, the objective validity of clear and distinct ideas, and the real distinction between mind and body. Instead, they focused on various domains of the natural sciences themselves: physics, anatomy, optics, and meteorology. Among these early works, particular prominence is given to Descartes’ posthumously published anatomical treatise Treatise on Man, which constitutes the second part of his unfinished project The World from the early 1630s, whose first part is the physical treatise Treatise on Light. It is also necessary to include Descartes’ work on optics, the Dioptrics, which offers his most detailed account of the mechanism of vision, and his treatise on weather, the Meteorology, both written in the same period.

Linking Descartes’ theory of cognitive faculties to the natural sciences in the strict sense will also make it possible to distinguish his theory of cognition from intellectualist interpretations and to situate it within the history of the natural sciences. Above all, it will place it in a different relation to contemporary scientific theories of cognition, which understand cognition as an embodied process.