JRWB

“I grant that the Soul in a waking Man is never without Thought, because it is the Condition of being awake: But whether Sleeping without Dreaming be not an Affection of the whole Man, Mind as well as Body, may be worth a waking Man’s Consideration; it being hard to conceive that any thing should think, and not be conscious of it. If the Soul doth think in a sleeping Man, without being conscious of it, I ask, whether, during such Thinking, it has any Pleasure or Pain, or be capable of Happiness or Misery? I am sure the Man is not, no more than the Bed or Earth he lies on. For to be Happy or Miserable, without being conscious of it, seems to me utterly inconsistent and impossible; or if it be possible that the Soul can, whilst the Body is sleeping, have its Thinking, Enjoyments and Concerns, its Pleasure or Pain apart, which the Man is not conscious of, nor partakes in: It is certain, that Socrates asleep, and Socrates awake, is not the same Person: But his Soul when he sleeps, and Socrates the Man, consisting of Body and Soul when he is waking, are two Persons; since waking Socrates has no Knowledge of, or Concernment for that Happiness or Misery of his Soul, which it enjoys alone by it self whilst he sleeps, without perceiving any thing of it; no more than he has for the Happiness or Misery of a Man in the Indies, whom he knows not. For if we take wholly away all Consciousness of our Actions and Sensations, especially of Pleasure and Pain, and the Concernment that accompanies it, it will be hard to know wherein to place Personal Identity.”

John Locke, An Essay concerning human understanding in 4 books, (Edmund Parker: London, 1731) vol.1 of 2. p.72-3