ccur in
succession. We cannot get beyond or behind the facts--and therefore
intuitionism in this sense is not opposed to empiricism, but a warrant
for empirical conclusions. An 'intuition,' briefly, is an unanalysable
belief. Brown asserts that a certain element of thought has not been
explained, and assumes it to be therefore inexplicable or ultimate.
Brown's account of causation had a great influence upon both the
Mills, and especially affected the teaching of the younger Mill.

Another point is important. Reid, as I have said, had specially prided
himself upon his supposed overthrow of Berkeley's idealism. He was
considered to have shown, in spite of sceptics, that the common belief
in an external world was reasonable. Brown in his lectures ridiculed
Reid's claim. This 'mighty achievement,' the 'supposed overthrow of a
great system,' was 'nothing more than the proof that certain phrases
are metaphorical, which were intended by their authors to be
understood _only_ as metaphors.'[480] The theory was dead before Reid
slew it, though the phrases were still used as a mere 'relic,' or
survival of an obsolete doctrine.[481] The impossibility of
constructing extension out of our sensations is the _experimentum
crucis_ upon which Reid was ready to stake his case. If the attempt at
such a construction could succeed, he would 'lay his hand upon his
mouth' and give up the argument.[482] Brown takes up the challenge
thus thrown out. He holds that our knowledge of an external world is
derived from a source which Reid overlooked. He modifies the Scottish
psychology by introducing the muscular senses. His theory is that the
infant which has learned to move discovers that on some occasions its
movements are modified by a sense of 'impeded effort.'[483] The sudden
interruption to a well-known series excites in its mind the notion of
'a cause which is not in itself.' This is the source of our belief in
an external world. That belief is essentially the belief in some cause
which we know to be other than our own mental constitution or the
series of 'internal' phenomena, and of which we can know nothing else.
It is enough to indicate a theory which has been elaborated by later
psychologists, and plays a great part (for example) in the theories of
Mill, Bain, and Mr. Herbert Spencer. It shows the real tendency of
Brown's speculations. In the first place, it must be noticed that the
theory itself had been already emphatically stated by Des