Where Hobbes is commonly thought of as the first modern political philosopher, Descartes is generally considered the founder of modern philosophy. According to Russell, Descartes is modern in that while he is influenced by the scholastics and the ancients, he seeks to create a new philosophy, and shows a creativity not seen in philosophy since Plato. Like Plato, he writes like an explorer rather than a teacher, and his literary style is in Russell’s words “extraordinarily excellent”.

I Think Therefore I Am

If the role of a philosopher is to understand the world, they must be able to determine what is real and what is not – they must have a theory of knowledge. The question of what is real is at the heart of Plato’s theory of ideas, and is the basis for Descartes’ most important philosophical work. Why not assume that everything we see around us is real? Several reasons, suggests Descartes: we might be dreaming, we might be mad and suffering hallucinations, or we might be deceived by an evil demon (!). The point is that we cannot know for certain that the world around us is real (had Descartes watched The Matrix, he might have added that scenario to his list). However, if we can think then we must have a mind which exists, and since mind is our essence it is enough to then say that we exist. To put it more succinctly: if I think, therefore I am. For Descartes this is something that we can know for certain, and even the most ardent sceptic could not deny it. It is therefore a firm foundation for his philosophy. Descartes then asks what else we can know. He first develops the ontological argument to prove to his satisfaction the existence of God; however Russell chooses to discuss this in relation to Leibniz who apparently expressed it better, so I will do the same.  Descartes deduces that if the mind definitively exists, then those things that we can perceive most clearly and precisely with our minds are most likely to exist as we perceive them. Knowledge based on geometry and mathematics are examples of this. I’ll briefly note Descartes significant contribution to mathematics as the inventor of the coordinate geometry system, where a point in space is described by its distance from fixed lines. In terms of what is real or true about material objects, knowledge that we derive through our senses (sight and touch etc) is less real and liable to be confused. Objects can, for example, change their properties and exhibit different properties over time. Real knowledge of objects comes from processing the inputs from our senses in our minds in order to understand them. The mind is central to understanding reality.

Separation of Mind & Matter

Where some philosophers had considered mind to be another type of matter, Descartes is consistent with Plato and Christian philosophy in treating mind as separate to matter. He is also a product of the mechanistic age in which he lived, and believed that the behaviour of all matter is entirely deterministic and governed by the laws of physics. This includes plants and animals, which do not have minds and in this respect are like machines. With sufficient understanding it would be possible to describe nature mathematically, such as the process by which a seed grows into a plant. In humans the physical body and the mind are separate, but Descartes believed they interact to some extent. Many of his followers believed the two are so different that it is impossible for them to interact, and that our physical movements are also entirely predetermined by physical laws. This doesn’t feel like it is true – it feels like our physical actions are controlled by our minds. The response was to say that the actions of both mind and body are predetermined by the same mechanical laws, such that while it seems like mind is controlling body, in fact they are both being controlled together by mechanical laws, which have been instituted by God. The analogy of the two clocks was used to explain this. Imagine there are two clocks perfectly in time with each other, and designed such that when one points to the hour the other will strike. It would appear to the casual observer that one had caused the other to strike, but in fact they are both independently following predetermined laws. Mind and body are to be viewed as two parts of a single machine, set in motion by God. As a result of this rigid determinism, Descartes and members of the Cartesian school did have trouble accepting the principle of free will. Indeed, some would go further than Descartes and think of humans as machines or robots, removing Descartes’ distinction between humans and other living things.