s also evident that
colours, sounds, &c., are originally on the same footing with the
pain that arises from steel, and pleasure that proceeds from a
fire; and that the difference betwixt them is founded neither on
perception nor reason, but on the imagination. For as they are
confessed to be, both of them, nothing but perceptions arising from
the particular configurations and motions of the parts of body,
wherein possibly can their difference consist? Upon the whole,
then, we may conclude that, as far as the senses are judges, all
perceptions are the same in the manner of their existence."--(I. p.
250, 251.)

The last words of this passage are as much Berkeley's as Hume's. But,
instead of following Berkeley in his deductions from the position thus
laid down, Hume, as the preceding citation shows, fully adopted the
conclusion to which all that we know of psychological physiology tends,
that the origin of the elements of consciousness, no less than that of
all its other states, is to be sought in bodily changes, the seat of
which can only be placed in the brain. And, as Locke had already done
with less effect, he states and refutes the arguments commonly brought
against the possibility of a causal connexion between the modes of
motion of the cerebral substance and states of consciousness, with great
clearness:--

"From these hypotheses concerning the _substance_ and _local
conjunction_ of our perceptions we may pass to another, which is
more intelligible than the former, and more important than the
latter, viz. concerning the _cause_ of our perceptions. Matter and
motion, 'tis commonly said in the schools, however varied, are
still matter and motion, and produce only a difference in the
position and situation of objects. Divide a body as often as you
please, 'tis still body. Place it in any figure, nothing ever
results but figure, or the relation of parts. Move it in any
manner, you still find motion or a change of relation. 'Tis absurd
to imagine that motion in a circle, for instance, should be nothing
but merely motion in a circle; while motion in another direction,
as in an ellipse, should also be a passion or moral reflection;
that the shocking of two globular particles should become a
sensation of pain, and that the meeting of the triangular ones
should afford a pleasure. Now as these di