In truth, the ideas Descartes was outlining were not really that new. Aristotle had a similar thought when he said that ‘to perceive that we perceive or think is to perceive that we exist.’ St Augustine, the 5th-Century philosopher, did too, when he responded to sceptical arguments by replying that ‘if I am mistaken, I exist.’ Jean de Silhon, a friend of Descartes, had toyed with similar formulations. But the history of ideas is not the history of the people who first thought of them. More often than not, it is the history of the person who popularised them.
