A BIRD IN HAND

At first sight, most people will read these statements as “a bird in the hand’ and ‘once upon a time.’ However, this is not what they actually say. . . . Our perception is distorted here because our familiarity with these phrases -- or, more accurately, with the phrases which these are designed to mimic -- creates an expectation which our perceptual system fulfill. According to Adlbert Ames’s transactionalist account of perception, this kind of perceptual ‘filling in’ is not unusual; retinal images are ambiguous, so our perceptual systems necessarily infer from past experience, and sometimes they get things wrong.

While these demonstrations of the fallibility of perception are illuminating and fun, they will not convince anybody that our brains systematically mislead us about the nature of the world. It will be objected that we should expect occasional mistakes; that there are lots of mechanisms available to allow us to check the veracity of our perceptual experiences (not least, we can hold them up against the experiences of other people); and that the very fact that we can identify mistakes allows that our brains work just fine most of the time.

This counter-argument is both absolutely right, and yet inadequate to see of the sceptical challenge. It is inadequate because there is a second response one can make to the original argument (there there’s no good evidence to show we are misled about the nature of the world). Put simply, one can object to this argument that it misses the force of the sceptical challenge. In order to talk about evidence, about the rational assessment of arguments, and so on, it is necessary to presuppose precisely what is being denied; namely, that we have grounds to think that the brain -- just conscious meat, after all -- is the kind of entity which is able to generate accurate knowledge about the world. - page 30/31