Thomas Reid (1785)
Essays on the Intellectual Powers of Man. Essay Three: Of Memory

Chapter 4:

Of Identity


The conviction which every man has of his identity, as far back as his memory reaches, needs no aid of philosophy to strengthen it; and no philosophy can weaken it, without first producing some degree of insanity.

The philosopher, however, may very properly consider this conviction as a phenomenon of human nature worthy of his attention. If he can discover its cause, an addition is made to his stock of knowledge; if not, it must be held as a part of our original constitution, or an effect of that constitution produced din a manner unknown to us.

We may observe, first of all, that this conviction is indispensably necessary to all exercise of reason. The operations of reason, whether in action or in speculation, are made up of successive parts. The antecedent are the foundation of the consequent, and, without the conviction that the antecedent have been seen or done by me, I could have no reason to proceed to the consequent, in any speculation, or in any active project whatever.

There can be no memory of what is past without the conviction that we existed at the time remembered. There may be good arguments to convince me that I existed before the earliest thing I can remember; but to suppose that my memory reaches a moment farther back than my belief and conviction of my existence, is a contradiction.

The moment a man loses this conviction, as if he had drunk the water of Lethe, past things are done away; and, in his own belief, he then begins to exist. Whatever was thought, or said, or done, or suffered before that period, may belong to some other person; but he can never impute it to himself, or take any subsequent step that supposes it to be his doing.

From this it is evident that we must have the conviction of our own continued existence and identity, as soon as we are capable of thinking or doing anything, on account of what we have thought, or done, or suffered before; that is, as soon as we are reasonable creatures.

That we may form as distinct a notion as we are able of this phenomenon of the human mind, it is proper to consider what is meant by identity in general, what by our own personal identity, and how we are led into that invincible belief and conviction which every man has of his own personal identity, as far as his memory reaches.

Identity in general I take to be a relation between a thing which is known to exist at one time, and a thing which is known to have existed at another time. If you ask whether they are one and the same, or two different things, every man of common sense understands the meaning of your question perfectly. Whence we may infer with certainty, that every man of common sense has a clear and distinct notion of identity.

If you ask a definition of identity, I confess I can give none; it is too simple a notion to admit of logical definition: I can say it is a relation, but I cannot find words to express the specific difference between this and other relations, though I am in no danger of confounding it with any other. I can say that diversity is a contrary relation, and that similitude and dissimilitude are another couple of contrary relations, which every man easily distinguishes in his conception from identity and diversity.

I see evidently that identity supposes an uninterrupted continuance of existence. That which has ceased to exist cannot be the same with that which afterwards begins to exist; for this would be to suppose a being to exist after it ceased to exist, and to have had existence before it was produced, which are manifest contradictions. Continued uninterrupted existence is therefore necessarily implied in identity.

Hence we may infer, that identity cannot, in its proper sense, be applied to our pains, our pleasures, our thought, or any operation of our minds. The pain felt this day is not the same individual pain which I felt yesterday, though they may be similar in kind and degree, and have the same cause. The same may be said of every feeling, and of every operation of mind. They are all successive in their nature, like time itself, no two moments of which can be the same moment.

It is otherwise with the parts of absolute space. They always are, and were, and will be the same. So far, I think, we proceed upon clear ground in fixing the notion of identity in general.

It is perhaps more difficult to ascertain with precision the meaning of personality; but it is not necessary in the present subject: it is sufficient for our purpose to observe, that all mankind place their personality in something that cannot be divided or consist of parts.

A part of a person is a manifest absurdity. When a man loses his estate, his health, his strength, he is still the same person, and has lost nothing of his personality. If he has a leg or an arm cut off, he is the same person he was before. The amputated member is no part of his person, otherwise it would have a right to a part of his estate, and be liable for a part of hie engagements. It would be entitled to a share of his merit and demerit, which is manifestly absurd. A person is something indivisible, and is what Leibniz calls a monad.

My personal identity, therefore, implies the continued existence of that indivisible thing which I call myself. Whatever this self may be, it is something which thinks, and deliberates, and resolves, and acts, and suffers. I am not thought, I am not action, I am not feeling; I am something that thinks, and acts, and suffers. My thoughts, and actions, and feelings, change every moment: they have no continued, but a successive, existence; but that self, or I, to which they belong, is permanent, and has the same relation to all the succeeding thoughts, actions, and feelings which I call mine.

Such are the notions that I have of my personal identity. But perhaps it may be said, this may all be fancy without reality. How do you know-what evidence have you-that there is such a permanent self which has a claim to all the thoughts, actions, and feelings which you call yours?

To this I answer, that the proper evidence I have of all this is remembrance, I remember that twenty years ago I conversed with such a person; I remember several things that passed in that conversation: my memory testifies, not only that this was done, but that it was done by me who now remember it. If it was done by me, I must have existed at that time, and continued to exist from that time to the present: if the identical person whom I call myself had not a part in that conversation, my memory is fallacious; it gives a distinct and positive testimony of what is not true. Every man in his senses believes what he distinctly remembers, and every thing he remembers convinces him that he existed at the time remembered.

Although memory gives the most irresistible evidence of my being the identical person that did such a thing, at such a time, I may have other good evidence of things which befell me, and which I do not remember: I know who bare me, and suckled me, but I do not remember these events.

It may here be observed (though the observation would have been unnecessary, if some great philosophers had not contradicted it), that it is not my remembering any action of mine that makes me to be the person who did it. This remembrance makes me to know assuredly that I did it; but I might have done it, though I did not remember it. That relation to me, which is expressed by saying that I did it, would be the same, though I had not the least remembrance of it. To say that my remembering that I did such a thing, or, as some choose to express it, my being conscious that I did it, makes me to have done it, appears to me as great an absurdity as it would be to say, that my belief that the world was created made it to be created.

When we pass judgment on the identity of other persons than ourselves, we proceed upon other grounds, and determine from a variety of circumstances, which sometimes produce the firmest assurance, and sometimes leave room for doubt. The identity of persons has often furnished matter of serious litigation before tribunals of justice. But no man of a sound mind ever doubted of his own identity, as far as he distinctly remembered.

The identity of a person is a perfect identity: wherever it is real, it admits of no degrees; and it is impossible that a person should be in part the same, and in part different; because a person is a monad, and is not divisible into parts. The evidence of identity in other persons than ourselves does indeed admit of all degrees, from what we account certainty, to the least degree of probability. But still it is true, that the same person is perfectly the same, and cannot be so in part, or in some degree only.

For this cause, I have first considered personal identity, as that which is perfect in its kind, and the natural measure of that which is imperfect.

We probably at first derive our notion of identity from that natural conviction which every man has from the dawn of reason of his own identity and continued existence. The operations of our minds are all successive, and have no continued existence. But the thinking being has a continued existence, and we have an invincible belief, that it remains the same when all its thoughts and operations change.

Our judgments of the identity of objects of sense seem to be formed much upon the same grounds as our judgments of the identity of other persons than ourselves.

Wherever we observe great similarity, we are apt to presume identity, if no reason appears to the contrary. Two objects ever so like, when they are perceived at the same time, cannot be the same; but if they are presented to our senses at different times, we are apt to think them the same, merely from their similarity.

Whether this be a natural prejudice, or from whatever cause it proceeds, it certainly appears in children from infancy; and when we grow up, it is confirmed in most instances by experience: for we rarely find two individuals of the same species that are not distinguishable by obvious differences.

A man challenges a thief whom he finds in possession of his horse or his watch, only on similarity. When the watchmaker swears that he sold this watch to such a person, his testimony is grounded on similarity. The testimony of witnesses to the identity of a person is commonly grounded on no other evidence.

Thus it appears, that the evidence we have of our own identity, as far back as we remember, is totally of a different kind from the evidence we have of the identity of other persons, or of objects of sense. The first is grounded on memory, and gives undoubted certainly. The last is grounded on similarity, and on other circumstances, which in many cases are not so decisive as to leave no room for doubt.

It may likewise be observed, that the identity of objects of sense is never perfect. All bodies, as they consist of innumerable parts that may be disjoined from them by a great variety of causes, are subject to continual changes of their substance, increasing, diminishing, changing insensibly. When such alterations are gradual, because language could not afford a different name for every different state of such a changeable being, it retains the same name, and is considered as the same thing. Thus we say of an old regiment, that it did such a thing a century ago, though there now is not a man alive who then belonged to it. We say a tree is the same in the seed-bed and in the forest. A ship of war, which has successively changed her anchors, her tackle, her sails, her masts, her planks, and her timbers, while she keeps the same name, is the same.

The identity, therefore, which we ascribe to bodies, whether natural or artificial, is not perfect identity; it is rather something which, for the convenience of speech, we call identity. It admits of a great change of the subject, providing the change be gradual; sometimes, even of a total change. And the changes which is common language are made consistent with identity differ from those that are thought to destroy it, not in kind, but in number and degree. It has no fixed nature when applied to bodies; and questions about the identity of a body are very often questions about words. But identity, when applied to persons, has no ambiguity, and admits not of degrees, or of more and less. It is the foundation of all rights and obligations, and of all accountableness; and the notion of it is fixed and precise.



Chapter 6:

Of Mr. Locke’s Account

Of Our Personal Identity

In a long chapter upon Identity and Diversity, Mr. Locke has made many ingenious and just observations, and some which I think cannot be defended. I shall only take notice of the account he gives of our own personal identity. His doctrine upon this subject has been censured by Bishop Butler, in a short essay subjoined to his Analogy, with whose sentiments I perfectly agree.

Identity, as was observed (Chap. 4 of this Essay), supposes the continued existence of the being of which it is affirmed, and therefore can be applied only to things which have a continued existence. While any being continues to exist, it is the same being; but two beings which have a different beginning or a different ending of their existence cannot possibly by the same. To this, I think, Mr. Locke agrees.

He observes, very justly, that, to know what is meant by the same person, we must consider what the word person stands for; and he defines a person to be an intelligent being, endowed with reason and with consciousness, which last he thinks inseparable from thought.

From this definition of a person, it must necessarily follow, that, while the intelligent being continues to exist and to be intelligent, it must be the same person. To say that the intelligent being is the person, and yet that the person ceases to exist while the intelligent being continues, or that the person continues while the intelligent being ceases to exist, is to my apprehension a manifest contradiction.

One would think that the definition of a person should perfectly ascertain the nature of personal identity, or wherein it consists, though it might still be a question how we come to know and be assured of our personal identity.

Mr. Locke tells us, however, "that personal identity, that is, the sameness of a rational being, consists in consciousness alone, and, as far as this consciousness can be extended backwards to any past action or thought, so far reaches the identity of that person. So that whatever has the consciousness of present and past actions is the same person to whom they belong."

This doctrine has some strange consequences, which the author was aware of. Such as, that if the same consciousness can be transferred from one intelligent being to another, which he thinks we cannot show to be impossible, then two or twenty intelligent beings may be the same person. And if the intelligent being may lose the consciousness of the actions done by him, which surely is possible, then he is not the person that did those actions; so that one intelligent being may be two or twenty different persons, if he shall so often lose the consciousness of this former actions.

There is another consequence of this doctrine, which follows no less necessarily, though Mr. Locke probably did not see it. It is, that a man may be, and at the same time not be, the person that did a particular action.

Suppose a brave officer to have been flogged when a boy at school for robbing an orchard, to have taken a standard from the enemy in his first campaign, and to have been made a general in advanced life; suppose, also, which must be admitted to be possible, that, when he took the standard, he was conscious of his having been flogged at school, and that, when made a general, he was conscious of his taking the standard, but had absolutely lost the consciousness of his flogging.

These things being supposed, it follows, from Mr. Locke’s doctrine, that he who was flogged at school is the same person who took the standard, and that he who took the standard is the same person who was made a general. Whence it follows, if there be any truth in logic, that the general is the same person with him who was flogged at school. But the general’s consciousness does not reach so far back as his flogging; therefore, according to Mr. Locke’s doctrine, he is not the person who was flogged. Therefore the general is, and at the same time is not, the same person with him who was flogged at school.

Leaving the consequences of this doctrine to those who have leisure to trace them, we may observe, with regard to the doctrine itself,

First, that Mr. Locke attributes to consciousness the conviction we have of our past actions, as if a man may now be conscious of what he did twenty years ago. It is impossible to understand the meaning of this, unless by consciousness he meant memory, the only faculty by which we have an immediate knowledge of our past actions.

Sometimes, in popular discourse, a man says he is conscious that he did such a thing, meaning that he distinctly remembers that he did it. It is unnecessary, in common discourse, to fix accurately the limits between consciousness and memory. This was formerly shown to be the case with regard to sense and memory: and therefore distinct remembrance is sometimes called sense, sometimes consciousness, without any inconvenience.

But this ought to be avoided in philosophy, otherwise we confound the different powers of the mind, and ascribe to one what really belongs to another. If a man can be conscious of what he did twenty years or twenty minutes ago, there is no use for memory, nor ought we to allow that there is any such faculty. The faculties of consciousness and memory are chiefly distinguished by this, that the first is an immediate knowledge of the present, the second an immediate knowledge of the past.

When, therefore, Mr. Locke’s notion of personal identity is properly expressed, it is, that personal identity consists in distinct remembrance: for, even in the popular sense, to say that I am conscious of a part action means nothing else than that I distinctly remember that I did it.

Secondly, it may be observed, that, in this doctrine, not only is consciousness confounded with memory, but, which is still more strange, personal identity is confounded with the evidence which we have or our personal identity.

It is very true, that my remembrance that I did such a thing is the evidence I have that I am the identical person who did it. And this, I am apt to think, Mr. Locke meant. But to say that my remembrance that I did such a thing, or my consciousness, makes me the person who did it, is, in my apprehension, an absurdity too gross to be entertained by any man who attends to the meaning of it; for it is to attribute to memory or consciousness a strange magical power of producing its object, though that object must have existed before the memory or consciousness which produced it.

Consciousness is the testimony of one faculty; memory is the testimony of another faculty; and to say that the testimony is the cause of the thing testified, this surely is absurd, if any thing be, and could not have been said by Mr. Locke, if he had not confounded the testimony with the thing testified.

When a horse that was stolen is found and claimed by the owner, the only evidence he can have, or that a judge or witnesses can have, that this is the very identical horse which was his property, is similitude. But would it not be ridiculous from this to infer that the identity of a horse consists in similitude only? The only evidence I have that I am the identical person who did such actions is, that I remember distinctly I did them; or, as Mr. Locke expresses it, I am conscious I did them. To infer from this, that personal identity consists in consciousness, is an argument which, if it had any force, would prove the identity of a stolen horse to consist solely in similitude.

Thirdly, is it not strange that the sameness or identity of a person should consist in a thing which is continually changing, and is not any two minutes the same?

Our consciousness, our memory, and every operation of the mind, are still flowing like the water of a river, or like time itself. The consciousness I have this moment can no more be the same consciousness I had last moment, than this moment can be the last moment. Identity can only be affirmed of things which have a continued existence. Consciousness, and every kind of thought, are transient and momentary, and have no continued existence; and, therefore, if personal identity consisted in consciousness, it would certainly follow, that no man is the same person any two moments of his life; and as the right and justice of reward and punishment are founded on personal identity, no man could be responsible for his actions.

But though I take this to be the unavoidable consequence of Mr. Locke’s doctrine concerning personal identity, and though some persons may have liked the doctrine the better on this account, I am far from imputing any thing of this kind to Mr. Locke. He was too good a man not to have rejected with abhorrence a doctrine which he believed to draw this consequence after it.

Fourthly, there are many expressions used by Mr. Locke, in speaking of personal identity, which to me are altogether unintelligible, unless we suppose that he confounded that sameness or identity which we ascribed to an individual with the identity which, in common discourse, is often ascribed to many individuals of the same species.

When we say that pain and pleasure, consciousness and memory, are the same in all men, this sameness can only mean similarity, or sameness of kind. That the pain of one man can be the same individual pain with that of another man is no less impossible, than that one man should be another man: the pain felt by me yesterday can no more be the pain I feel to-day, than yesterday can be this day; and the same thing may be said of every passion and of every operation of the mind. The same kind or species of operation may be in different men, or in the same man at different times; but it is impossible that the same individual operation should be in different men, or in the same man at different times.

When Mr. Locke, therefore, speaks of "the same consciousness being continued through a succession of different substances;" when he speaks of "repeating the idea of a past action, with the same consciousness we had of it at the first," and of "the same consciousness extending to actions past and to come"; these expressions are to me unintelligible, unless he means not the same individual consciousness, but a consciousness that is similar, or of the same kind.

If our personal identity consists in consciousness, as this consciousness cannot be the same individually any two moments, but only of the same kind, it would follow, that we are not for any two moments the same individual persons, but the same kind of persons.

As our consciousness sometimes ceases to exist, as in sound sleep, our personal identity must cease with it. Mr. Locke allows, that the same thing cannot have two beginnings of existence, so that our identity would be irrecoverably gone every time we ceased to think, if it was but for a moment.