ion.

There remained only one possible position, which, had it been taken up
earlier, might have saved an immensity of trouble; and that was to
affirm that we do not, and cannot, know anything about the "substance"
either of the thinking thing, or of the extended thing. And Hume's sound
common sense led him to defend this thesis, which Locke had already
foreshadowed, with respect to the question of the substance of the soul.
Hume enunciates two opinions. The first is that the question itself is
unintelligible, and therefore cannot receive any answer; the second is
that the popular doctrine respecting the immateriality, simplicity, and
indivisibility of a thinking substance is a "true atheism, and will
serve to justify all those sentiments for which Spinoza is so
universally infamous."

In support of the first opinion, Hume points out that it is impossible
to attach any definite meaning to the word "substance" when employed for
the hypothetical substratum of soul and matter. For if we define
substance as that which may exist by itself, the definition does not
distinguish the soul from perceptions. It is perfectly easy to conceive
that states of consciousness are self-subsistent. And, if the substance
of the soul is defined as that in which perceptions inhere, what is
meant by the inherence? Is such inherence conceivable? If conceivable,
what evidence is there of it? And what is the use of a substratum to
things which, for anything we know to the contrary, are capable of
existing by themselves?

Moreover, it may be added, supposing the soul has a substance, how do we
know that it is different from the substance, which, on like grounds,
must be supposed to underlie the qualities of matter?

Again, if it be said that our personal identity requires the assumption
of a substance which remains the same while the accidents of perception
shift and change, the question arises what is meant by personal
identity?

"For my part," says Hume, "when I enter most intimately into what I
call _myself_, I always stumble on some particular perception or
other, of heat or cold, light or shade, love or hatred, pain or
pleasure. I never can catch _myself_ at any time without a
perception, and never can observe anything but the perception. When
my perceptions are removed for any time, as by sound sleep, so long
am I insensible of _myself_, and may be truly said not to exist.
And were all my percepti