be incapable of attaching any meaning to
subjectivity. The flux of things would then go on in their own medium,
not in our minds; and no suspicion of illusion or of qualification by
mind would attach to any event in nature. So it is in a dream; and it is
our knowledge of physics, our reliance on the world's material
coherence, that marks our awakening, and that constitutes our discovery
that we exist as minds and are subject to dreaming. It is quite true
that the flux, as it exists in men, is largely psychic; but only because
the events it contains are effects of material causes and the images in
it are flying shadows cast by solid external things. This is the meaning
of psychic existence, and its differentia. Mind is an expression,
weighted with emotion, of mechanical relations among bodies. Suppose the
bodies all removed: at once the images formerly contrasted with those
bodies would resume their inherent characteristics and mutual relation;
they would become existences in their own category, large, moving,
coloured, distributed to right and left; that is, save for their values,
they would become material things.

[Sidenote: It recurs in all understanding of perception.]

Physics is accordingly a science which, though hypothetical and only
verifiable by experiment, is involved in history and psychology and
therefore in any criticism of knowledge. The contradiction would be
curious if a man should declare that his ideas were worthless, being due
to his organs of sense, and that therefore these organs (since he had an
idea of them) did not exist. Yet on this brave argument idealism chiefly
rests. It asserts that bodies are mere ideas, because it is through our
bodies that we perceive them. When physics has discovered the conditions
under which knowledge of physics has arisen, physics is supposed to be
spirited away; whereas, of course, it has only closed its circle and
justified its sovereignty. Were all science retracted and reduced to
symbolic calculation nothing would remain for this calculation to
symbolise. The whole force of calling a theory merely a vehicle or
method of thought, leading us to something different from itself, lies
in having a literal knowledge of this other thing. But such literal
knowledge is the first stage of science, which the other stages merely
extend. So that when, under special circumstances, we really appeal to
algebraic methods of expression and think in symbols, we do so in the
hope of