e belief was held to be that which men in general, or in the
long run, or on the average, hold true, as distinguished from what the
individual under variable and accidental influences holds true. And even
in the case of introspection we found that true cognition resolved
itself into a consensus or agreement as to certain psychical facts.

_Criterion of Illusion._

Now, it behoves us here to examine this assumption, with the view of
seeing how far it is perfectly sound. For it may be that what is
commonly held true does not in all cases strictly answer to the real, in
which case our idea of illusion would have to be extended so as to
include certain common beliefs. This question was partly opened up at
the close of the last chapter. It will be found that the full
discussion of it carries us beyond the scientific point of view
altogether. For the present, however, let us see what can be said about
it from that standpoint of positive science to which we have hitherto
been keeping.

Now, if by common be meant what has been shared by all minds or the
majority of minds up to a particular time, a moment's inspection of the
process of correcting illusion will show that science assumes the
possibility of a common illusion. In the history of discovery, the first
assault on an error was the setting up of the individual against the
society. The men who first dared to say that the sun did not move round
the earth found to their cost what it was to fly in the face of a
common, though illusory, perception of the senses.[151]

If, however, by common be understood what is permanently and unshakably
held true by men in proportion as their minds become enlightened, then
science certainly does assume the truth of common perception and belief.
Thus, the progress of the physical sciences may be described as a
movement towards a new, higher, and more stable consensus of ideas and
beliefs. In point of fact, the truths accepted by men of science already
form a body of common belief for those who are supposed by all to have
the means of testing the value of their convictions. And the same
applies to the successive improvements in the conceptions of the moral
sciences, for example, history and psychology. Indeed, the very meaning
of science appears to be a body of common cognition to which all minds
converge in proportion to their capabilities and opportunities of
studying the particular subject-matter concerned.

Not only so, from a stric