“Descartes sets out in his quest for certainty by thinking first about the evidence that comes through the senses: seeing, touching, smelling, tasting and hearing. Can we trust our senses? Not really, he concluded. The senses sometimes trick us. We make mistakes. Think about what you see. Is your sight reliable about everything? Should you always believe your eyes?
A straight stick put in water seems bent if you look at it from the side. A square tower in the distance might look round. We all occasionally make mistakes about what we see. And, Descartes points out, it would be unwise to trust something that has tricked you in the past. So he rejects the senses as a possible source of certainty. He can never be sure that his senses aren’t tricking him. They probably aren’t most of the time, but the faint possibility that they might be means he can’t completely rely on them. But where does that leave him?”
— Nigel Warburton, A Little History of Philosophy
Also in the series, David Crystal’s A Little Book of Language & E H Gombrich’s A Little History of the World