percepts, are just as good as those of others; the only objection to them is that, as their context is
unusual, they are apt to give rise to fallacious inferences.
But how about inferences? Are they equally personal and private? In a sense, we must admit that
they are. What I am to believe, I must believe because of some reason that appeals to me. It is true
that my reason may be some one else's assertion, but that may be a perfectly adequate reason--for
instance, if I am a judge listening to evidence. And however Protagorean I may be, it is reasonable
to accept the opinion of an accountant about a set of figures in preference to my own, for I may
have repeatedly found that if, at first, I disagree with him, a little more care shows me that he was
right. In this sense I may admit that another man is wiser than I am. The Protagorean position,
rightly interpreted, does not involve the view that I never make mistakes, but only that the
evidence of my mistakes must appear to me. My past self can be judged just as another person can
be judged. But all this presupposes that, as regards inferences as opposed to percepts, there is
some impersonal standard of correctness. If any inference that I happen to draw is just as good as
any other, then the intellectual anarchy that Plato deduces from Protagoras does in fact follow. On
this point, therefore, which is an important one, Plato seems to be in the right. But the empiricist
would say that perceptions are the test of correctness in inference in empirical material.
(3) The doctrine of universal flux is caricatured by Plato, and it is difficult to suppose that any one
ever held it in the extreme form that he gives to it. Let us suppose, for example, that the colours
we see are continually changing. Such a word as "red" applies to many shades of colour, and if we
say "I see red," there is no reason why this should not remain true throughout the time that it takes
to say it. Plato gets his results by applying to processes of continuous change such logical
oppositions as perceiving and not-perceiving, knowing and not-knowing. Such oppositions,
however, are not suitable for describing such processes. Suppose, on a foggy day, you watch a
man walking away from you along a road: he grows dimmer and dimmer, and there comes a
moment when you are sure that you no longer see him, but there is an intermediate period of
doubt. Logical oppositions have been invented for our convenience, but continuous change
requires a quantitative apparatus, the possibility of which Plato