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If a sleeping Man thinks without knowing it, the sleeping and waking Man are two Persons.       §12. The Soul, during sound Sleep, thinks, say these Men. Whilst
it thinks and perceives, it is capable certainly of those of Delight or
Trouble, as well as any other Perceptions; and it must necessarily be
conscious of its own Perceptions. But it has all this apart: The sleeping
Man, ’tis plain, is conscious of nothing of all this. Let us suppose
then the Soul of Castor, whilst he is sleeping, retired from his Body,
which is no impossible Supposition for the Men I have here to do
with, who so liberally allow Life, without a thinking Soul to all
other Animals. These Men cannot then judge it impossible, or a
contradiction, That the Body should live without the Soul; nor
that the Soul should subsist and think, or have Perception, even
Perception of Happiness or Misery, without the Body. Let us then,
as I say, suppose the Soul of Castor separated, during his Sleep, from
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his Body, to think apart. Let us suppose too, that it chuses for its
Scene of Thinking, the Body of another Man, v.g. Pollux, who is
sleeping without a Soul: For if Castor’s Soul can think whilst Castor
is asleep, what Castor is never conscious of, ’tis no matter what
Place it chuses to think in. We have here then the Bodies of two
Men with only one Soul between them, which we will suppose to
sleep and wake by turns; and the Soul still thinking in the waking
Man, whereof the sleeping Man is never conscious, has never the
least Perception. I ask then, Whether Castor and Pollux, thus, with
only one Soul between them, which thinks and perceives in one,
what the other is never conscious of, nor is concerned for, are not
two as distinct Persons, as Castor and Hercules; or, as Socrates and
Plato were? And whether one of them might not be very happy, and
the other very miserable? Just by the same Reason, they make the
Soul and the Man two Persons, who make the Soul think apart,
what the Man is not conscious of. For, I suppose, no body will make
Identity of Persons, to consist in the Sou’ls being united to the very
same numerical Particles of matter: For if that be necessary to
Identity, ’twill be impossible, in that constant flux of the Particles
of our Bodies, that any Man should be the same Person, two days,
or two moments together.
Locke Hum II, 1, §12, pp. 110-111