Big Thinker Rene Descartes

René Descartes (1596-1650) is famous for the line, “I think therefore I am”. He was a Frenchman writing in the early 17th Century and was preoccupied with the question of what can we know for certain?

Descartes details a method of doubt in his key text Meditations on First Philosophy, published in 1641. It becomes crucial for Rationalists that seek infallible knowledge. Rationalists rest their epistemological claims on pure Reason, without recourse to the senses or experience (unlike the Empiricists). Epistemology is the philosophical study of knowledge.

At a time when scholars were writing in Latin, Descartes wrote in French so anyone who was literate in the common language of his place could read his work. His writing style is friendly and approachable, so it feels as though you are having a conversation with him. His sceptical inquiry into what we can know commences with the question:

Can my senses be trusted?

Descartes describes himself sitting in front of a log fire in his wood cabin, smoking a pipe and questioning whether or not he can be sure that he is awake and alert as opposed to asleep and dreaming. How can we know the difference, he asks, when sometimes, in our dream state, we feel as though we’re awake even though we’re not?

Using the first person point of view, Descartes ponders on the fact that he tends to use his senses to be sure he exists and that the world around him is real, but the senses can sometimes be deceived. Our eyes often play tricks on us – as proven by any optical illusion – so how can we trust something that tricks us even once?

What can we know for certain? Image: Warner Bros

Cartesian scepticism (Cartesian being the adjective to describe the school of Decartes’ thought) concludes ultimately all I can be truly sure of is that I am a thinking thing. Descartes’ famously declared:

“Cogito ergo sum: I think therefore I am.”

Descartes posits the only thing I can be sure of is that I exist because even when I doubt that, there is an “I” doing the doubting. The “I” that thinks or doubts, must surely exist, he claims.

For Descartes the mind is more knowable than the body, and he equates the human Soul with the mind. For him, the mind is the essence of a person.

As a mathematician and a ‘natural scientist’ Descartes sought to prove that truths of the world were as immutable as rational, logical mathematic proofs. After he has proven that “I think, therefore I am” is as secure a foundation for knowledge as “1 + 1 = 2” Descartes goes on to use a thought experiment in order to consider whether we can be sure God exists.

The Evil Genius thought experiment

Descartes’ thought experiment of the evil genius asks us to imagine there exists, instead of an entirely good and powerful God, an entirely powerful, all-knowing Malevolent Demon. The idea here is that this Demon could make us think we are experiencing the world as it truly is, but we aren’t really. We could be tricked by this Evil Genius, and we may not be able to trust any knowledge we receive about the world from our senses. Ultimately Descartes relies upon an Ontological or Rational Argument to prove that God exists and if God exists, then we can trust our senses as God would not fool us in such a way as the Evil Demon might.

The incredibly powerful questions Descartes asks still inform many of our science fiction fears as we wonder whether or not the world truly is as it appears to us. We can still see the power of doubting and if we take this worry too seriously, we can imagine being paralysed with fear, unable to do anything! Many of us accept that our senses can be tricked but we know that we just have to go on trusting them anyway and hope for the best.

This sceptical method Descartes outlines whereby we check what we believe to be true and question what we assume to be real is useful if we think of it in terms of seeking evidence for the beliefs we are taught and the assumptions we hold. Considered in this way, Descartes offers us a great tool for self-reflection. However, if we take this thought experiment seriously we may never be sure that even we ourselves exist!

David Hume, writing in the 18th Century suggested that the even the assumption that there is an ‘I’ that doubts is an illusion as all we have to go on is a string of conscious experiences. Whether I truly am awake or dreaming right now is something I may not be able to answer with 100 percent accuracy, and this doubt is expanded upon and played with to wonderful effect in films such as The Matrix and Inception.

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Can your senses be trusted?