t (rational idealism)? These are some of the questions in
philosophy which still await their final answer.

Philosophy being thus still a question and not a solution, we need not
here trouble ourselves about its problems further than to remark on
their close connection with our special subject, the study of illusion.

Our brief reference to some of the principal inquiries of philosophy
shows that it tends to throw doubt on things which the unreflecting
popular mind holds to be indubitable. Different schools of philosophy
have shown themselves unequally concerned about these so-called
intuitive certainties. In general it may be said that philosophy,
though, as I have remarked, theoretically free to set up its own
standard of certainty, has in practice endeavoured to give a meaning
to, and to find a justification for the assumptions or first principles
of science. On the other hand, it has not hesitated, when occasion
required, to make very light of the intuitive beliefs of the popular
mind as interpreted by itself. Thus, rationalists of the Platonic type
have not shrunk from pronouncing individual impressions and objects
illusory, an assertion which certainly seems to be opposed to the
assumptions of common sense, if not to those of science. On the other
hand, the modern empirical or association school is quite ready to
declare that the vulgar belief in an external world, so far as it
represents this as independent of mind,[154] is an illusion; that the
so-called necessary beliefs respecting identity, uniformity, causation,
etc., are not, strictly speaking, necessary; and so on. And in these
ways it certainly seems to come into conflict with popular convictions,
or intuitive certainties, as they present themselves to the unreflecting
intelligence.

Philosophy seems, then, to be a continuation of that process of
detecting illusion with which science in part concerns itself. Indeed,
it is evident that our special study has a very close connection with
the philosophic inquiry. What philosophy wants is something intuitively
certain as its starting-point, some _point d'appui_ for its
construction. The errors incident to the process of reasoning do not
greatly trouble it, since these can, in general, be guarded against by
the rules of logic. But error in the midst of what, on the face of it,
looks like intuitive knowledge naturally raises the question, Is there
any kind of absolutely certain cognition, any organ for the accu