he other, to inquire into
the nature of the steps by which they become metamorphosed into those
compound states of consciousness, which so largely enter into our
ordinary trains of thought.

With respect to the origin of impressions of sensation, Hume is not
quite consistent with himself. In one place (I. p. 117) he says, that it
is impossible to decide "whether they arise immediately from the object,
or are produced by the creative power of the mind, or are derived from
the Author of our being," thereby implying that realism and idealism are
equally probable hypotheses. But, in fact, after the demonstration by
Descartes, that the immediate antecedents of sensations are changes in
the nervous system, with which our feelings have no sort of resemblance,
the hypothesis that sensations "arise immediately from the object" was
out of court; and that Hume fully admitted the Cartesian doctrine is
apparent when he says (I. p. 272):--

"All our perceptions are dependent on our organs and the
disposition of our nerves and animal spirits."

And again, though in relation to another question, he observes:--

"There are three different kinds of impressions conveyed by the
senses. The first are those of the figure, bulk, motion, and
solidity of bodies. The second those of colours, tastes, smells,
sounds, heat, and cold. The third are the pains and pleasures that
arise from the application of objects to our bodies, as by the
cutting of our flesh with steel, and such like. Both philosophers
and the vulgar suppose the first of these to have a distinct
continued existence. The vulgar only regard the second as on the
same footing. Both philosophers and the vulgar again esteem the
third to be merely perceptions, and consequently interrupted and
dependent beings.

"Now 'tis evident that, whatever may be our philosophical opinion,
colour, sounds, heat, and cold, as far as appears to the senses,
exist after the same manner with motion and solidity; and that the
difference we make between them, in this respect, arises not from
the mere perception. So strong is the prejudice for the distinct
continued existence of the former qualities, that when the contrary
opinion is advanced by modern philosophers, people imagine they can
almost refute it from their reason and experience, and that their
very senses contradict this philosophy. 'Ti