Certainty and doubt: Descartes

Independence from authority

Rene Descartes attacks not only Aristotelianism, but also, more generally, authority.

Immanuel Kant: ‘Have courage to use your own reason!’

Knowledge and opinion

Descartes claims that philosophers have relied on Aristotle’s opinions’.

Knowledge is more certain than opinion. If our opinions are true, but we cannot prove that they are true, they do not constitute knowledge and do not warrant certainty.

Belief’ is neutral; we can have true or false beliefs, justified as well as unjustified beliefs.

Source: Wikimedia

Why should we prefer knowledge to opinion?

Having knowledge frees one from authority. Consider how education is commonly withdrawn from underclasses (Out of Africa scene), plus women’s education.

Descartes’s Meditations and the quest for certainty

Philosophies of knowledge such as Descartes’s are normally called foundationalist, precisely because they are aimed at establishing some basic beliefs (or foundations) that do not depend on any other beliefs.

Descartes would say that only absolutely certain beliefs can be said to be part of knowledge.

The method of doubt

To reject opinions ‘it will be enough if I find in each of them at least some reason for doubt’. He goes straight to the basic beliefs on which all others rest. Doubting his beliefs is a method for attaining knowledge.

The first step in the method of doubt: examining the reliability of the senses

Can we trust the senses? Objects far away from us look smaller than objects near us.

The second step in the method of doubt: the dream hypothesis

We cannot be sure that we are not dreaming; if we are, the objects that we see around us could just be part of our dream, and so could our bodies.

He goes a step further, and doubts any opinions formed on evidence provided by the senses.

Descartes distinguishes between two groups of sciences: the sciences in one group include physics and astronomy (which study objects that exist in nature); the sciences in the other group include arithmetic and geometry (which study objects ‘regardless of whether they really exist in nature’).

a priori and a posteriori knowledge: the dream hypothesis does not undermine a priori knowledge.

The third step in the method of doubt: the ‘malicious demon’ hypothesis

Descartes argues that he cannot rule out the hypothesis that the world has been created and is governed not by a benign God but by a malicious demon, who deceives human beings in all possible ways. It could make us believe that a square has five angles, and that 2 + 3 makes 4.

Finding certainty: the cogito

“I too undoubtedly exist, if he is deceiving me”

Descartes concludes that since he thinks, then he must exist: ‘I am, I exist’ cannot be doubted.

“At present I am not admitting anything except what is necessarily true. I am, then, in the strict sense only a thing that thinks; that is, I am a mind, or intelligence, or intellect, or reason … I am a thing which is real and which truly exists. But what kind of a thing? As I have just said – a thinking thing.”

That I, as a thinking thing, as a mind, exist is the only certainty at this stage of Descartes’s reflection.

Hume’s objection to Descartes’s use of doubt: scepticism and knowledge

A modern objection to Descartes’s method

John Cottingham criticises Descartes’s aim to present a new method of discovery and his aim to find an absolutely certain belief on which to build our system of knowledge. Not only does Cottingham believe that Descartes has not succeeded in attaining these aims, but he also argues that these aims are not attainable.

He targets the two fundamental parts of Descartes’s method: the possibility of discovering a fixed number of fundamental truths; and that of devising a perfect method to develop knowledge on those fundamental truths.

Why read Descartes nowadays?

What we take to be knowledge needs justifying.

This justification of knowledge can be pursued by each of us.