g" ought to be meaningless to a man who, having never had
experience of one, is compelled to represent it by the aid of something
so different from it as ideas are supposed to be. Can material things
really be to such a creature anything more than some complex of ideas?

The difficulties presented by any philosophical doctrine are not always
evident at once. Descartes made no scruple of accepting the existence
of an external world, and his example has been followed by a very large
number of those who agree with his initial assumption that the mind
knows immediately only its own ideas.

Preeminent among such we must regard John Locke, the English
philosopher (1632-1704), whose classic work, "An Essay concerning Human
Understanding," should not be wholly unknown to any one who pretends to
an interest in the English literature.

Admirably does Locke represent the position of what very many have
regarded as the prudent and sensible man,--the man who recognizes that
ideas are not external things, and that things must be known through
ideas, and yet holds on to the existence of a material world which we
assuredly know.

He recognizes, it is true, that some one may find a possible opening
for the expression of a doubt, but he regards the doubt as gratuitous;
"I think nobody can, in earnest, be so skeptical as to be uncertain of
the existence of those things which he sees and feels." As we have
seen (section 12), he meets the doubt with a jest.

Nevertheless, those who read with attention Locke's admirably clear
pages must notice that he does not succeed in really setting to rest
the doubt that has suggested itself. It becomes clear that Locke felt
so sure of the existence of the external world because he now and then
slipped into the inconsistent doctrine that he perceived it
immediately, and not merely through his ideas. Are those things "which
he sees and feels" _external_ things? Does he see and feel them
directly, or must he infer from his ideas that he sees and feels them?
If the latter, why may one not still doubt? Evidently the appeal is to
a direct experience of material things, and Locke has forgotten that he
must be a Lockian.

"I have often remarked, in many instances," writes Descartes, "that
there is a great difference between an object and its idea." How could
the man possibly have remarked this, when he had never in his life
perceived the object corresponding to any idea, but had been altogether
s