Rene Descartes

(1596 – 1650)

French philosopher and mathematician. He is often called the father of modern philosophy and is credited for the increased attention given to epistemology in the 17th century. He laid the groundwork for modern rationalism and is one of the most important contributors and figures of the Age of Reason or the Enlightenment. Descartes was also one of the key figures in the Scientific Revolution – among other things, he developed analytic geometry and the coordinate system with the x and y axis, a key feature in mathematics we all know.

His most famous work are the Meditations on First Philosophy (1641), which is one of the most influential and most widely read philosophical texts ever. The book is made up of six meditations, each representing a day where Descartes meditates in his chair, in order to discover a firm foundation of absolute certainty, upon which he could build a new system of knowledge. The method he chooses is radical (Cartesian) doubt – that is, he doubts everything, no matter how weak or implausible it seems to doubt it, in order to discover something that is unquestionably true. In the process of meditating, he comes to the following:

He shows that everything we might know from our senses could be wrong, since they often deceive us (for example, in optical or other kinds of illusions).
He goes on to show that even the physical reality could be an illusion, since he could be dreaming, and in dreams one generally doesn’t know that what appears is not real.
He then shows that even the rules of mathematics could be doubted, because there is a slight chance that an Evil Genius was deceiving him, and simple mathematical propositions (such as 1+1=2) could be false.
What else if left? Descartes discovers, that even if his senses are deceiving him, even if he is dreaming, even if a demon is deceiving him, there is one truth that cannot be doubted, formulated in his most famous saying: “Cogito, ergo sum” – I think therefore I am. No matter if everything around him would turn out to be false, that even his body wasn’t real, he cannot doubt the existence of his mind.

Having found this benchmark of certainty, he continues to build the rest of his knowledge system. He starts with pure sense data or immediate perceptions of the mind, which are certain if they don’t make references to the outer world (for example, I can know certainly that “I am experiencing cold”, but not necessarily that “the room is cold” – because there would need to be certainty that the room exists at all). He also discovers, that beside immediate sense data, the mind also contains four innate ideas (cf. Plato’s Forms) – the self (the “I”), substance (thoughts), identity (the “thing” that thinks), which are all evident from himself as a thinking being. The last one is God, a perfect being, for which he offers an interesting proof:

(Descartes’s proof of God): (1) Because he doubts, he is not perfect (if he was perfect, he would know everything and would not doubt). (2) Even though he is not perfect, somehow, he has an idea of perfection. (3) How else could he have an idea of perfection, or of a perfect being, in himself, when there is nothing in him or outside that would cause the idea. (4) Therefore, a perfect being (God) exists.

All of the above is the foundation for Cartesian Dualism and Rationalism.

Rationalism is the belief that the true source of knowledge is the reason (the mind/soul), not the senses
Dualism is the position that the mind and body are distinct and separate – they are independent and mutually exclusive substances. This position gives rise to the famous mind-body problem.

—> The problem is: how do the mind and body interact, or form a unity? (We know from experience that they do – I think about taking a step, and my body takes a step). Descartes tried to solve the problem by claiming that the mind and the body meet in the centre of the brain, in the pineal gland, which attracted a lot of criticism.