With ‘same man’ in hand, let us turn to ‘same person’. To find what personal identity consists in, we must consider what ‘person’ stands for.

I think it is a thinking intelligent being, that has reason and reflection, and can consider itself as itself, the same thinking thing at different times and places. What enables it to think of itself is its consciousness, which is inseparable from thinking and (it seems to me) essential to it.

It is impossible for anyone to perceive, without perceiving that he perceives. When we see, hear, smell, taste, feel, meditate, or will anything, we know that we do so. It is always like that with our present sensations and perceptions. And it is through this that everyone is to himself that which he calls ‘self, not raising the question of whether the same self is continued in the same substance.

Consciousness always accompanies thinking, and makes everyone to be what he calls ‘self’ and thereby distinguishes himself from all other thinking things; in this alone consists personal identity, i.e. the sameness of a rational being; and as far as this consciousness can be extended backwards to any past action or thought, so far reaches the identity of that person; it is the same self now that it was then; and this present self that now reflects on it is the one by which that action was performed.

Given that it is the same person, is it the same identical substance? Most people would think that it is the same substance if these perceptions with their consciousness always remained present in the mind, making the same thinking thing always consciously present and (most people would think) evidently the same to itself. What seems to make the difficulty— that is, to make it at least questionable whether the same person must be the same substance— is the following fact.

Consciousness is often interrupted by forgetfulness, and at no moment of our lives do we have the whole sequence of all our past actions before our eyes in one view; even the best memories lose the sight of one part while they are viewing another.

Furthermore, for the greatest part of our lives we don’t reflect on our past selves at all, because we are intent on our present thoughts or (in sound sleep) have no thoughts at all, or at least none with the consciousness that characterizes our waking thoughts. In all these cases our consciousness is interrupted, and we lose the sight of our past selves, and so doubts are raised as to whether or not we are the same thinking thing, i.e. the same substance.

That may be a reasonable question, but it has nothing to do with personal identity. For the latter, the question is about what makes the same person, and not whether the same identical substance always thinks in the same person. Different substances might all partake in a single consciousness and thereby be united into one person, just as different bodies can enter into the same life and thereby be united into one animal, whose identity is preserved throughout that change of substances by the unity of the single continued life. What makes a man be himself to himself is sameness of consciousness, so personal identity depends entirely on that—whether the consciousness is tied to one substance throughout or rather is continued in a series of different substances. For as far as any thinking being can repeat the idea of any past action with the same consciousness that he had of it at first, and with the same consciousness he has of his present actions, so far is he the same personal self. For it is by the consciousness he has of his present thoughts and actions that he is self to himself now, and so will be the same self as far as the same consciousness can extend to actions past or to come. Distance of time doesn’t make him two or more persons, and nor does change of substance; any more than a man is made to be two men by having a long or short sleep or by changing his clothes.

Our own bodies give us some kind of evidence for this. All the particles of your body, while they are vitally united to a single thinking conscious self—so that you feel when they are touched, and are affected by and conscious of good or harm that happens to them—are a part of yourself, i.e. of your thinking conscious self. Thus, the limbs of his body are to everyone a part of himself; he feels for them and is concerned for them. Cut off a hand and thereby separate it from that consciousness the person had of its heat, cold, and other states, and it is then no longer a part of himself, any more than is the remotest material thing. Thus, we see the substance of which the personal self consisted at one time may be varied at another without change of personal identity; for there is no doubt that it is the same person, even though one of its limbs has been cut off.

But it is asked: Can it be the same person if the substance changes? and Can it be different persons if the same substance does the thinking throughout?

Before I address these questions in sections 13 and 14, there’s a preliminary point I want to make. It is that neither question is alive for those who hold that thought is a property of a purely material animal constitution, with no immaterial substance being involved. Whether or not they are right about that, they obviously conceive personal identity as being preserved in something other than identity of substance; just as animal identity is preserved in identity of life, not of substance. This pair of questions does present a challenge to those who hold that only immaterial substances can think, and that sameness of person requires sameness of immaterial substance.

Before they can confront their materialist opponents, they have to show why personal identity can’t be preserved through a change of immaterial substances, just as animal identity is preserved through a change of material substances. Unless they say that what makes the same life and thus the animal identity in lower animals is one immaterial spirit, just as (according to them) one immaterial spirit makes the same person in men—and Cartesians at least won’t take that way out, for fear of making the lower animals thinking things too.

As to the first question, If the thinking substance is changed, can it be the same person? I answer that this can be settled only by those who know what kind of substances they are that think, and whether the consciousness of past actions can be transferred from one such substance to another.

Admittedly, if the same consciousness were the same individual action, it couldn’t be transferred because in that case bringing a past headache (say) into one’s consciousness would be bringing back that very headache, and that is tied to the substance to which it occurred. But a present consciousness of a past event isn’t like that. Rather it is a present representation of a past action, and we have still to be shown why something can’t be represented to the mind as having happened though really it did not. How far the consciousness of past actions is tied to one individual agent, so that another can’t possibly have it, will be hard for us to determine until we know what kind of action it is that can’t be done without a reflex act of perception accompanying it, and how such an action is done by thinking substances who can’t think without being conscious of it. In our present state of knowledge, it is hard to see how it can be impossible, in the nature of things, for an intellectual substance to have represented to it as done by itself something that it never did, and was perhaps done by some other agent…. Until we have a clearer view of the nature of thinking substances, we had better assume that such changes of substance within a single person never do in fact happen, basing this on the goodness of God. Having a concern for the happiness or misery of his creatures, he won’t transfer from one substance to another the consciousness that draws reward or punishment with it. …

The second question, Can it be different persons if the same substance does the thinking throughout? seems to me to arise out of the question of whether the following is possible:

An immaterial being that has been conscious of the events in its past is wholly stripped of all that consciousness, losing it beyond the power of ever retrieving it again; so that now it (as it were) opens a new account, with a new starting date, having a consciousness that can’t reach back beyond this new state.

Really, the question is whether if this happened it could be the same person who had first one consciousness and then another, with no possibility of communication between them. [Locke says that this must be regarded as possible by ‘those who hold preexistence’, that is, who believe in reincarnation. He attacks them, thereby attacking the separation of ‘same person’ from ‘same consciousness’, and proposes a thought experiment:] Reflect on yourself, and conclude that you have in yourself an immaterial spirit that is what thinks in you, keeps you the same throughout the constant change of your body, and is what you call ‘myself’. Now try to suppose also that it is the same soul that was in Nestor or Thersites at the siege of Troy. This isn’t obviously absurd; for souls, as far as we know anything of their nature, can go with any portion of matter as well as with any other; so the soul or thinking substance that is now yourself may once really have been the soul of someone else, such as Thersites or Nestor. But you don’t now have any consciousness of any of the actions either of those two; so can you conceive yourself as being the same person with either of them? Can their actions have anything to do with you? Can you attribute those actions to yourself, or think of them as yours more than the actions of any other men that ever existed? Of course you can’t ….

So we can easily conceive of being the same person at the resurrection, though in a body with partly different parts or structure from what one has now, as long as the same consciousness stays with the soul that inhabits the body. But the soul alone, in the change of bodies, would not be accounted enough to make the same man—except by someone who identifies the soul with the man. If the soul of a prince, carrying with it the consciousness of the prince’s past life, were to enter and inform the body of a cobbler who has been deserted by his own soul, everyone sees that he would be the same person as the prince, accountable only for the prince’s actions; but who would say it was the same man? The body contributes to making the man, and in this case, I should think everyone would let the body settle the ‘same man’ question, not dissuaded from this by the soul, with all its princely thoughts. To everyone but himself he would be the same cobbler, the same man. I know that in common parlance ‘same person’ and ‘same man’ stand for the same thing; and of course everyone will always be free to speak as he pleases, giving words what meanings he thinks fit, and changing them as often as he likes. Still, when we want to explore what makes the same spirit, man, or person, we must fix the ideas of spirit, man, or person in our minds; and when we have become clear about what we mean by them, we shan’t find it hard to settle, for each of them, when it is ‘the same’ and when not.

But although the same immaterial substance or soul does not by itself, in all circumstances, make the same man, it is clear that consciousness unites actions—whether from long ago or from the immediately preceding moment—into the same person. Whatever has the consciousness of present and past actions is the same person to whom they both belong. If my present consciousness that I am now writing were also a consciousness that I saw an overflowing of the Thames last winter and that I saw Noah’s ark and the flood, I couldn’t doubt that I who write this now am the same self that saw the Thames overflowed last winter and viewed the flood at the general deluge—place that self in what substance you please. I could no more doubt this than I can doubt that I who write this am the same myself now while I write as I was yesterday, whether or not I consist of all the same substance, material or immaterial. For sameness of substance is irrelevant to sameness of self: I am as much involved in—and as justly accountable for— an action that was done a thousand years ago and is appropriated to me now by this self-consciousness as I am for what I did a moment ago.

Self is that conscious thinking thing that feels or is conscious of pleasure and pain and capable of happiness or misery, and so is concerned for itself as far as that consciousness extends. (This holds true whatever substance the thinking thing is made up of; it doesn’t matter whether it is spiritual or material, simple or compounded.) You must find that while your little finger is brought under your consciousness it is as much a part of yourself as is your head or your heart. If the finger were amputated and this consciousness went along with it, deserting the rest of the body, it is evident that the little finger would then be the person, the same person; and this self would then would have nothing to do with the rest of the body. As with spatial separation so also with temporal: something with which the consciousness of this present thinking thing can join itself makes the same person, and is one self with it, as everyone who reflects will perceive.

Personal identity is the basis for all the right and justice of reward and punishment. What everyone is concerned for, for himself, is happiness and misery—with no concern for what becomes of any substance that isn’t connected with that consciousness. [Locke goes on to apply that to his ‘finger’ example, supposing that the finger takes the original consciousness with it, and that the rest of the body acquires a new consciousness.]

This illustrates my thesis that personal identity consists not in the identity of substance but in the identity of consciousness. If Socrates and the present mayor of Queenborough agree in that, they are the same person; if Socrates awake doesn’t partake of the same consciousness as Socrates sleeping, they aren’t the same person. And to punish Socrates awake for something done by sleeping Socrates without Socrates awake ever being conscious of it would be as unjust as to punish someone for an action of his twin brother’s merely because their outsides were so alike that they couldn’t be distinguished.

It may be objected: ‘Suppose I wholly lose the memory of some parts of my life beyond any possibility of retrieving them, so that I shall never be conscious of them again; aren’t I still the same person who did those actions, had those thoughts that I once was conscious of, even though I have now forgotten them?’ To this I answer that we must be careful about what the word ‘I’ is applied to. This objector is thinking of sameness of the man, and calls it ‘I’ because he assumes that the same man is the same person. But the assumption isn’t necessarily correct . If one man could have distinct disconnected consciousnesses at different times, that same man would certainly make different persons at different times. That this is what people in general think can be seen in the most solemn declaration of their opinions: human laws don’t punish the madman for the sane man’s actions, or the sane man for what the madman did, because they treat them as two persons. This is reflected in common speech when we say that someone is ‘not himself or is ‘beside himself’. Those phrases insinuate that the speaker thinks—or that those who coined the phrases thought—that the self was changed, the self-same person was no longer in that man.

‘It is still hard to conceive that Socrates, the same individual man, might be two persons.’ To help us with this we must consider what is meant by ‘Socrates’, or ‘the same individual man’. There are three options . The same man might be any of these:

• the same individual, immaterial, thinking substance; in short, the numerically same soul and nothing else,
• the same animal, without any regard to an immaterial soul,
• the same immaterial spirit united to the same animal.

Help yourself! On any of these accounts of ‘same man’, it is impossible for personal identity to consist in anything but consciousness, or reach any further than that does. According to 1, a man born of different women, and in distant times, might still be the same man. Anyone who allows this must also allow that the same man could be two distinct persons. . . . According to 2 and 3, Socrates in this life cannot be the same man as anyone in the afterlife. The only way to do this— allowing for the possibility that Socrates in Athens and Socrates in Limbo are the same man— is through an appeal to sameness of consciousness; and that amounts to equating human identity— ‘same man’— with personal identity. But that equation is problematic, because it makes it hard to see how the infant Socrates can be the same man as Socrates after the resurrection. There seems to be little agreement about what makes a man, and thus about what makes the same individual man; but whatever we think about that, if we are not to fall into great absurdities we must agree that sameness of person resides in consciousness.

You may want to object: ‘But isn’t a man drunk and sober the same person? Why else is he punished for what he does when drunk, even if he is never afterwards conscious of it? He is just as much a single person as a man who walks in his sleep and is answerable, while awake, for any harm he did in his sleep.’ Here is my reply to that . Human laws punish both, with a justice suitable to the state of knowledge of those who administer the law: in these cases they can’t distinguish for sure what is real from what is counterfeit; and so they don’t allow the ignorance in drunkenness or sleep as a plea. Granted: punishment is tied to personhood, which is tied to consciousness, and the drunkard may not be conscious of what he did; but the courts justly punish him, because his bad actions are proved against him, and his lack of consciousness of them can’t be proved for him. It may be reasonable to think that on the great day when the secrets of all hearts are laid open, nobody will be held accountable for actions of which he knows nothing; everybody will receive his sentence with his conscience agreeing with God’s judgment by accusing or excusing him.

Nothing but consciousness can unite remote existences into the same person. The identity of substance won’t do it. For whatever substance there is, and whatever it is like, without consciousness there is no person. A substance without consciousness can no more be a person that a carcass can.

Citation and Use

The text was taken from the following work.

Locke, John. An Essay Concerning Humane Understanding, Volume 2. Project Gutenberg, 1694. https://www.gutenberg.org/ebooks/10616.

The use of this work is governed by the Public Domain.