the ambiguous term _sensible ideas_
unfortunately led to their being regarded as ideas derived, not from our
action in any form, but from pure sensation alone.

This extraordinary error was intensified in the speculation of Berkeley
and Hume. Experience with them appeared to consist solely of a
succession of sensations appearing to, impressing, or affecting a
_tabula rasa_ of consciousness.

Of course in such a state of affairs all Knowledge would be impossible.
The scepticism which logically followed from such a doctrine was too
universal to be capable even of the fiction that it was credible.
Berkeley, it is true, endeavoured to save the situation by postulating
the incessant and immediate intervention of the Deity as the sustainer
of the sensible panorama. This purely arbitrary and fictitious expedient
was entirely rejected by Hume, who with fearless honesty carried to its
ultimate results the direct consequences of the doctrine and then
complacently left human Knowledge to take care of itself.

* * * * *

A masterly protest against the position of Hume was made by his
countryman Reid, who in his _Inquiry into the Human Mind_ very clearly
pointed out the fundamental difference between the sensible
accompaniments or constituents of our Experience and the real and
independently existent substratum by which that Experience is sustained
and organised. His argument, though it attracted considerable attention,
did not, however, affect as deeply as might have been expected the
future of philosophic speculation, probably because he offered no new
clue or key whereby to detect the origin and account for the presence in
our Experience of those enduring and substantial elements or forms by
which it is sustained, but on the contrary left their recognition to
what he rather vaguely described as common sense.

* * * * *

Much more influential was the elaborate answer of Kant, which has
profoundly affected the course of Metaphysics since its publication.
Reverting in principle to the platonic method, Kant again sought the
enduring elements, the fundamentals of Science, in the constitution of
the cognitive faculty itself. But very differently from Plato he
discovered these in the categories or essential forms of intellective
action,--the category of causality and dependence and the so-called
forms of the transcendental aesthetic--Time and Space. Under these
categor