Philosophers often fantasize about starting from facts “given” by sense perception, building up the rest of their beliefs from this foundation. But this is a fantasy because sense experiences are themselves partly constructed by our prior beliefs: sense perception and thought seep into one other. But, argues Christopher Mole, this doesn’t mean that perception is always biased in favour of our prior convictions: on the contrary, the influence of belief on perception can help us better navigate the world.

Solvers of sudoku know that one sometimes gets into such a muddle that there is nothing for it but to start again. Errors in one place bring others in their train, so that the best thing to do may be to go back to a point before any error could have been made, discarding everything except for the numbers that were given initially. Philosophers have often fantasized about making a similarly fresh start with the whole assembled body of our beliefs, putting aside all of our variously acquired opinions – some of which will surely have been picked up erroneously – and going back to whatever facts were given to us in sense perception, before any erroneous assumptions had a chance to lead us astray.