new and
better standard of common cognition.

This scientific regulation of belief only fails where the experiences
which underlie the conceptions are individual, variable, and subjective.
Hence there is no definite common conception of the value of life and of
the world, just because the estimate of this value must vary with
individual circumstances, temperament, etc. All that can be looked for
here in the way of a common standard or norm is a rough average
estimate. And this common-sense judgment serves practically as a
sufficient criterion of truth, at least in relation to such extreme
one-sidedness of view as approaches the abnormal, that is to say, one of
the two poles of irrational exaltation, or "joy-madness," and abject
melancholy, which, appear among the phenomena of mental disease.[146]

CHAPTER XII.

RESULTS.

The foregoing study of illusions may not improbably have had a
bewildering effect on the mind of the reader. To keep the mental eye,
like the bodily eye, for any time intently fixed on one object is apt to
produce a feeling of giddiness. And in the case of a subject like
illusion, the effect is enormously increased by the disturbing character
of the object looked at. Indeed, the first feeling produced by our
survey of the wide field of illusory error might be expressed pretty
accurately by the despondent cry of the poet--

"Alas! it is delusion all:
The future cheats us from afar,
Nor can we be what we recall,
Nor dare we think on what we are."

It must be confessed that our study has tended to bring home to the mind
the wide range of the illusory and unreal in our intellectual life. In
sense-perception, in the introspection of the mind's own feelings, in
the reading of others' feelings, in memory, and finally in belief, we
have found a large field for illusory cognition. And while illusion has
thus so great a depth in the individual mind, it has a no less striking
breadth or extent in the collective human mind. No doubt its grosser
forms manifest themselves most conspicuously in the undisciplined mind
of the savage and the rustic; yet even the cultivated mind is by no
means free from its control. In truth, most of the illusions illustrated
in this work are such as can be shared in by all classes of mind.

In view of this wide far-reaching area of ascertained error, the mind
naturally asks, What are the real limits of illusory cognition, and how
can we be ever sure of having