Descartes and Treatise on Man

In his essay, Treatise on Man, Rene Descartes presents a theory concerning the inner-workings of man. He states that man is composed of two parts, body and soul. And his aim to explain how these two components function together to constitute man.

The Body

The body is a machine, like a clock or fountain. It moves according to its own power, which enables it to function. A clock ticks and thus functions to tell the time. A fountain pumps water to function as an ornamental display. So, what does it mean for the body to tick or pump?

According to Descartes, the answer lies in the heart. The heart pumps blood up into the brain via the arteries. As the arteries reach a particular gland in the brain, blood is filtered through small holes into the gland. Once the blood is filtered, it is no longer blood, but instead, something Descartes calls animal spirits. The animal spirits are a “very fine wind, or rather a very lively and pure flame” fueled by the heart that spurs the brain nerves forward into action. And it is these nerves that enable the movement of muscles and limbs.

To better understand the basic structure, let’s consider an example Descartes gives in the treatise.

Fountain Analogy

Consider a water fountain. Water is pumped into pipes, which creates pressure. This pressure, when released, enables the movement of certain ornamental displays of the fountain. The fountain can be interfered by some external force, like the wind, which can cause varying effects on the displays.

The heart is the water source or pump. The animal spirits is the water. The nerves are the pipes, in which water is stored. And the ornamental display is the muscles and limbs of the body. When a pipe is opened, the water animates the ornamental display. Sense organs act as external forces, like the wind, which changes the effects of the display.

According to Descartes, the body is purely a machine without a conscious intelligence. It is the same as man as for animal. For it to be constituted as man, a rational soul must occupy the place of the brain, and become the “fountain-keeper,” who oversees the fountain’s pipes and acts accordingly towards the fountain function.

The Soul

God unites the rational soul with the machine body. He seats the soul in the brain. In the brain, the soul takes account of the opening and closings of the pipes. For example, if I stub my toe, a pipe (or nerve) will open and make itself present to the soul as pain. It is the rational souls job to respond to such events. The many ways the pipes can be opened and closed explains the varied feelings that can be expressed: moisture, dryness, weight, heat, cold.

The gland within the brain receives input from the internal pipes of the brain. It is within this gland which common-sense and imagination arises. To better understand how this works, consider the figure below that Descartes presents in his treatise:

Object ABC (right) affects the gland abc (left) through the eyes. The rational soul resides in the gland and receives input from the tubes of the brain interior.

Let’s assume Object ABC is a pencil. I see the pencil. The yellowness, shape, shadow, of the of pencil trigger certain nerves in my eyes, thereby opening the tubes and releasing animal spirit. The way the tubes are opened and the combination of tubes opened constitute the size, colors, sounds, smells, and other perceptions received by the brain.

It is important to note that the Object ABC both imprints on the internal surface of the brain (pre-gland) and the surface of the gland. An idea is that which imprints upon the gland, and not the internal surface of the brain. Traces imprinted on the internal surface of the brain are instead called memory.

Memory results from path-making in the gaps produced by the current of the spirits. The more a certain stimulus happens, the stronger these gaps become and the more familiar with the stimulus. This solidifying of the paths creates a sense of semi-permeance which we call memory.

Conclusion

I should like you to consider, after this, all the functions I have ascribed to this machine — such as the digestion of food, the beating of the heart and arteries, the nourishment and growth of the limbs, respiration, waking and sleeping, the reception by the external sense organs of light, sounds, smells, tastes, heat and other such qualities, the imprinting of the ideas of these qualities in the organ of the ‘common’ sense and the imagination, the retention of stamping of these ideas in the memory, the internal movements of the appetites and passions, and finally the external movements of all the limbs

According to Descartes, the body is a machine. It is run via a pipe-like system of animal spirits which connects external stimuli with a gland in the brain where the rational soul resides. But the body is not sufficient to constitute man. An animal functions the same way. Instead, man must both include the body and the soul. And it is God that unites the two.