One and the same human being-while awake and while...

One and the same human being-while awake and while asleep-could participate in conscious lives that were as completely distinct from each other in the moral sense as are the distinct lives of identical twins. Even the legal tradition preserves this point by declining to punish a human being for actions performed while insane, since these crimes were, for all moral purposes, committed by a different person.

[Essay II xxvii 15-20] A morally adequate position must somehow account for personal identity without reference to either an immaterial soul or a living body. Consciousness and Accountability According to Locke, an appropriate account of personal identity must arise from careful analysis of the concept of the person.

Since self-conscious awareness invariably accompanies all human thought, it alone can both distinguish the self from every other thinking thing in the present and preserve its identity through time.

This being premised to find wherein personal Identity consists, we must consider what Person stands for; which, I think, is a thinking intelligent Being, that has reason and reflection, and can consider it self as it self, the same thinking thing in different times and places; which it does only by that consciousness, which is inseparable from thinking, and as it seems to me essential to it.

[Essay II xxvii 9] Since only consciousness of pleasure and pain can support both desire for one's own welfare and accountability for one's own actions, it is by consciousness alone that the self appropriates those present or past actions for which it now or in the future justly deserves to be punished or rewarded. [Essay II xxvii 23, 26] Consciousness is both a necessary and a sufficient condition for a morally vital sense of personal identity.

It is necessary because no past thought or action was truly mine unless I now self-consciously appropriate it to myself; and from this it follows that I cannot now be justly punished as the agent who committed some past action unless I am conscious of having performed that action myself.

[Essay II xxvii 18-20] It is sufficient because consciousness unites temporally distinct thoughts and actions from past, present, and future into a single person; since I can now harbor concern for the happiness or misery of the future self that would justly suffer punishment for my present transgressions, deliberation about those consequences are a relevent force in motivating my present conduct.