Descartes the Sceptic

Descartes thirsted for certainty. One of his philosophical legacies, which endured into the 19th century, was the practice of refusing to believe in anything which did not appear to him to be entirely certain. Fortunately for him he didn't live in the era of Heisenberg's Uncertainty Principle or Godel's Incompleteness Theorem.

To test his beliefs, Descartes developed a series of sceptical hypotheses. How, for example, could he be certain he was not dreaming? Perhaps an evil genius was trying to deceive him, pretending that the world exists, falsely leading him to conclude that 2 + 3 = 5…

Descartes concluded that an evil genius could not deceive someone into thinking they existed if they did not, because doubt itself cannot be doubted. Therefore the doubter must exist.

From this thought process derives Descartes’ famous ‘Cogito ergo sum’ or ‘I think therefore I am’. However, Descartes’ use of scepticism to reach certainty isn’t without its tiny problems. Philosophers still wrestle with what has become known as the Cartesian circle: no argument to show God exists can be certain unless you are certain of your own reasoning, but - according to Descartes - you cannot be certain of your reasoning unless you are certain God exists.

Tricky one…