"That with which the consciousness of this present thinking thing can join itself, makes the same person, and is one self with it, and with nothing else"(Locke).
What are the strengths and weaknesses of this account of self?

What is Locke's account of self?

Locke's account of "self", or personal identity, is presented as the culmination of his discussion of identity in general, in Book II, Chapter XXVII   - "Of Identity and Diversity"- of his "An Essay concerning Human Understanding"(1).   The first eight sections of the chapter present Locke's theory of identity in general.   The remaining sections, addressing the personal identity of the "self", present his application of this theory to persons.

One of Locke's intentions with his Essay was to provide an adequate philosophical foundation for the new Mechanical / Atomistic (Corpuscular) physics of Boyle and his compatriots.   With his presentation of a theory of identity, Locke's primary target was therefore the Scholastic variants of Aristotelianism.   The Scholastics maintained that each existent thing had a "substantial form" -- an underlying principle that was the cause of its being a single thing, the cause of its being a member of its species, and thus the criteria of its identity.   The forms provided the metaphysical basis of any existent's individual identity, powers, and operations. These "substantial forms"were thought of as Aristotelian "formal"causes in the context of the fourfold Aristotelian scheme of causes.   Hence any Scholastic explanation of the unity, operations, or powers of natural objects incorporated inescapable teleological considerations.   The Scholastics viewed "substantial forms"as real and actual constituents of existents.   The form was something over and above the matter of which the body was made.   Scholastic discussions of the principles of individuation and identity were speculations about what it is in a particular existent that gives it its identity, the real constituent of it that is the causal basis of its individuality.

In contrast to this Scholastic view of identity, Locke approaches the question of identity from a thoroughly mechanistic commitment to Boyle's corpuscularian physics.   He therefore rejects any thought of there being anything in an individual entity beyond the "corpuscles".   Locke's major break with the Scholastics is to recognize that it is our idea of the kind of thing whose identity is at issue which determines its identity.   As long as a spatio-temporally continuous series of masses of matter continues to satisfy our idea of the thing, we have the same thing.  

To conceive, and judge of [identity] aright, we must consider what Idea the word it is applied to stands for; It being one thing to be the same Substance, another the same Man, and a third the same Person, if Person, Man, and Substance, are three names standing for three different Ideas; for such as is the Idea belonging to that Name, such must be the Identity. (Essay II.xxvii.7)

It is our idea of the kind of thing whose identity is at issue which determines its identity.   There is no question of this idea's playing any causal role in the manner of a Scholastic "substantial form".   There is no sense in which the idea is a constituent of the thing.   As long as a spatio-temporally continuous series of coherent collections of atoms continues to satisfy the idea, we have the same thing.   In that sense, the idea keeps the thing the same.   And in Locke's ontology, there are three fundamentally different kinds of things to which the notion of identity attaches -- "We have the Ideas but of three sorts of Substances; 1. God. 2. Finite Intelligences. 3. Bodies."[Essay II.xxvii.2]

The first principle that Locke lays down is that "we rightly conclude, that whatever exists any where at any time, excludes all of the same kind, and is there it self alone"[Essay II, xxvii, 1].       By their solidity, atoms exclude all other material things from the volume of space which they at occupy at any given time.   By their physical indivisibility, atoms are immutable with respect to their figure, bulk, number, and unity.   Their only qualities which are subject to change are their state of motion and their position or situation.   Thus, the continued existence of an atom is simply a matter of its continuing to occupy space.   Atoms, then, constitute simple substances.   The identity of a complex mass of matter is given in terms of the identity of its constituent atoms.

He draws from this principle the corollary that two things A and B, of the same kind, are identical if and only if they have the same beginning of existence.   "[T]he relation [of spatio-temporal continuity] to [the determinate time and place of its beginning to exist] will always determine to each of them its Identity as long as it exists."[Essay II.xxvii.2]   For bodies and finite spirits, then, identity consists of spatio-temporal continuity.   For bodies and finite spirits, Locke adds the condition that there can be no addition or subtraction of matter to or from the mass of corpuscles (or atoms) that constitutes the thing if it is to continue to be the same thing.  

If two or more Atoms be joined together in the same Mass, every one of those Atoms will be the same, by the foregoing Rule: And whilst they exist united together, the Mass, consisting of the same Atoms, must be the same Mass, or the same Body, let the parts be never so differently jumbled; But if one of those Atoms be taken away, or one new one added, it is no longer the same Mass, or Body. [Essay II, xxvii, 2]

On Locke's view, then, a body remains the same (maintains the same identity) as long as it continues as a coherent unified collection of atoms, and as long as it suffers no addition or subtraction from that collection.   (Of course, this view entails that if one adds a room to a house, it is not the same house.)   By establishing this principle of the identity of material objects, Locke establishes that the identity conditions for material existents can be provided entirely in terms of things material.   There is no need of any extra "substantial form"to act as causative agent in the creation of identity.

Locke fully recognized that his material principle of identity for a mass of matter will simply not do for living things.   Living things do not maintain a coherent unified collection of atoms.   For living things, Locke extends his principle for material existents and draws instead on the mechanical organization of coherent unified collection of atoms that is life.   The organization of the collection establishes what is considered a "coherent unified collection".

We must therefore consider wherein an Oak differs from a Mass of Matter, and that seems to me to be in this; that the one is only the Cohesion of Particles of Matter any how united, the other such a disposition of them as constitutes the parts of an Oak; and such an Organization of those parts, as is fit to receive, and distribute nourishment, so as to continue, and frame the Wood, Bark, and Leaves, etc., of an Oak in which consists the vegetable Life. That being then one plant, which has such an Organization of Parts in one coherent Body, partaking of one Common Life, it continues to be the same Plant, as long as it partakes of the same Life, though that Live be communicated to new Particles of Matter vitally united to the living Plant, in a like continued Organization, conformable to that sort of Plants, For this Organization being at any one instant any one Collection of Matter, is in that particular concrete distinguished from all other, and is that individual Life, which existing constantly from that moment both forwards and backwards in the same continuity of insensibly succeeding Parts united to the living BO0dy of the Plant, it has that Identity, shich makes the same Plant, and all the parts of it, parts of the same Plant, during all the time that they exist united in that continued Organization which is fit to convey the Common Life to all the parts so united. [Essay II.xxvii.4]

For a lump of matter to have a particular life is simply for it to have an appropriate organization of parts.   But what determines whether any given organization is so "appropriate", is our idea of the particular thing.   Locke distinguished "nominal essences"from "real essences".   The real essence of any thing is the mechanical / atomistic constitution of the thing -- the causal basis of the thing's powers and qualities.   It's nominal essence, however, is our abstract idea of the sort to which the thing belongs.

But Essence, even in this sense, relates to a Sort, and supposes a Species: For being that real Constitution, on which the properties depend, it necessarily supposes a sort of Things, Properties belonging only to Species and not to individuals. [Essay III.vi.6]

So the nominal essence that we have identified, more or less arbitrarily, establishes the level of abstraction at which the internal structure of some living thing is to be discerned as appropriately organized.   And it is the nominal essence that a thing must continue to satisfy in order to remain the identical thing over time.   Hence the acorn and the mature oak remain the identical plant because the internal organization of the parts remains the same -- i.e. living -- and the qualities and powers of the plant remain within the species of oak plant over the course of time.   (Of course, this view entails that mother and daughter would constitute one Life until the umbilical chord is cut or the placenta ejected by the womb.)

Having set the groundwork with the establishment of mechanistic and atomistic criteria of identity for bodies (lumps of matter), and living things (organized lumps of matter), Locke is now ready to discuss the criteria of identity for persons -- the "self".   To start, Locke defines his terms.   He establishes that by "self"he means a consciousness that "can consider itself as itself".

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 itself as itself, 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: it being impossible for any one to perceive without perceiving that he does perceive. [Essay II.xxvii.9]

Locke argues that it is consciousness that defines the Self.   Whatever constitutes continuity of consciousness (and Locke does not directly explore this issue), it is this very continuity of consciousness that makes for personal identity, in parallel with the principle that continuity of life is what makes for the identity of living things.   It is continuity of consciousness that is the criteria of identity of the self over time, and across both bodies and substances (if and where these are possible).

Different Substances, by the same consciousness (where they do partake in it) being united into one Person; as well as different Bodies, by the same Life are united into one Animal, whose identity is preserved, in that change of Substances, by the unity of one continued Life. For, it being the same consciousness that makes a man be himself to himself, personal identity depends on that only, whether it be annexed solely to one individual substance, or can be continued in a succession of several substances. For as far as any intelligent being can repeat the idea of any past action with the same consciousness it had of it at first, and with the same consciousness it has of any present action; so far it is the same personal self. For it is by the consciousness it has of its present thoughts and actions, that it is self to itself now, and so will be the same self, as far as the same consciousness can extend to actions past or to come. and would be by distance of time, or change of substance, no more two persons, than a man be two men by wearing other clothes to-day than he did yesterday, with a long or a short sleep between: the same consciousness uniting those distant actions into the same person, whatever substances contributed to their production. [Essay II.xxvii.10]

Locke recognizes a distinction between the Body in which the consciousness resides, the Substance that does the thinking that is the consciousness, and the Consciousness that is the Self or Person.   The identity of the body is established by the identity criteria for living things previously established -- and establishes the identity of the same "man".   But the identity of the person is established by the identity criteria for consciousness -- and establishes the identity of the same Person or Self.   Locke does not address identity criteria for substances, because he takes a dim view of the Scholastic notion of substances, and would generally prefer to avoid using them.   His references to substances occur primarily to bridge the gap from the Scholastic traditions for which "substance"was a central ontological concept.   Notice how, in this next quote, he disassociates the conscious thing from any notion of substance, and refrains from establishing whether consciousness is "spiritual or material, simple or compounded".

Self depends on consciousness, not on substance. Self is that conscious thinking thing,�"whatever substance made up of, (whether spiritual or material, simple or compounded, it matters not)�"which is sensible or conscious of pleasure and pain, capable of happiness or misery, and so is concerned for itself, as far as that consciousness extends. . . . [I]t is the consciousness that goes along with the substance, when one part is separate from another, which makes the same person, and constitutes this inseparable self: so it is in reference to substances remote in time. That with which the consciousness of this present thinking thing can join itself, makes the same person, and is one self with it, and with nothing else; and so attributes to itself, and owns all the actions of that thing, as its own, as far as that consciousness reaches, and no further; as every one who reflects will perceive. [Essay II.xxvii.17]

For Locke, personal identity at a time consists in consciousness (self-awareness) at that time.   Personal identity over time consists in the continuity of consciousness (self-awareness) of an individual consciousness over that time.   The only remaining issue is just what is Locke's criteria for the continuity of consciousness.   Unfortunately, Locke is not entirely clear about this -- he does not discuss just how "this present thinking thing can join itself"to itself over time or space.   Although he does argue that memory is evidence for, in a sense a test or criterion of, the continuity of consciousness, he is quite clear that memory is not what personal identity consists in.  

He is clear, however, that his idea of personal identity is a forensic one.

Person, as I take it, is the name for this self.   Wherever a man finds, what he calls himself, there I think another may say is the same person.   It is a forensic term appropriating actions and their merit; and so belongs only to intelligent agents capable of a law, and happiness and misery.   [Essay II.xxvii.26]

He is also clear that "person"is independent of the "body".   With his thought experiment about the Prince and the Cobbler, Locke imagines that the "person"of the Prince can be switched to the body of the Cobbler.   And yet, in framing this scenario, Locke deepens the mystery of just what he means by "consciousness"and the confusion he raises with memory -- "For should the soul of a prince, carrying with it the consciousness [memory?!] of the prince's past life, enter and inform the body of a cobbler,…"[Essay II.xxvii.15]   And when referring to a man he'd met who believed his soul had been the soul of Socrates, Locke asks, "would any one say, that he, being not conscious of any of Socrates's actions or thoughts, could be the same person with Socrates?"[Essay II.xxvii.14]  

What are the strengths of Locke's account of self?

There are three primary strengths of Locke's account of self.   The first is that it is thoroughly consistent with our own subjective view of ourselves.   In fact, one might argue that Locke's theory of personal identity is an entirely subjective account -- relying completely on criteria available only within oneself, and not accessible to others.   The continuity of consciousness is entirely in the view of the "self", and readily spans real-time "gaps"in the temporal continuum.   Although there may be "gaps"in my consciousness from an objective perspective, as when I fall asleep and awake several hours later, there are no such "gaps"from within here where "I"exist.   There is no subjective time-span between my falling asleep and my awakening.

The second great strength of Locke's account of the self is that it does away completely with the Scholastic notions of "substance", "substantial form", and Aristotelian "formal cause".   Locke's account of identity in general is an entirely mechanistic and atomistic theory, in keeping with the new-atomism of the then current trends in physics.   The account of self, or personal identity, is based on the general account of identity, and is therefore equally founded on a non-Scholastic metaphysics.

The third great strength of Locke's account of self is its consistency with the forensic notions of personal responsibility.   It was not totally in accord with the judicial practice of his day, of course.   But his theories have informed and often guided the evolution of judicial reform since its publication.   Whether the issues are about amnesia, or drunkenness, or whatever -- the trend has been to regard Locke's theory of the self as the basis for assigning both accolades and punishments to the "agent"held responsible for the actions in question.

What are the weaknesses of Locke's account of self?

There are two primary weaknesses to Locke's account of the self.   The first is that Locke never established just what a continuity of consciousness consists in.   While he did accept memory as a test of that continuity, it was clearly not what he had in mind as what such continuity consists in.   It remains to a personal subjective judgment whether any two consciousnesses -- over time or over space -- are identical in the requisite sense.   There remains no objective criteria that may be applied.  

This means that there is no objective criteria against which to test veridical versus false judgements of the continuity of self.   Suppose (like Shirley MacLaine) I were to have a vivid and convincing memory of sailing down the Nile in the company of Cleopatra, and on that basis judged that my "self"(my "I") is continuous in the relevant sense with the body sailing the Nile .   There does not appear to be anything in Locke's account of the identity of "self"that would be able to test the veracity of that claim.

Similarly, if some agent claims not to remember the actions of which he is accused, then Locke's theory would maintain that there are two persons involved.   There is no way in Locke's account of the identity of the self, to check the veracity of the agent's claim.   So in such judicial cases as "multiple personality disorder", judicial practice tends to focus on the identity of the body rather than the identity of the self(s) involved.   The former can be objectified, while the latter cannot.

The other great weakness of Locke's account of the self also stems from the manner in which Locke treats the evidence of memory.

But yet possibly it will still be objected,�"Suppose I wholly lose the memory of some parts of my life, beyond a possibility of retrieving them, so that perhaps I shall never be conscious of them again; yet am I not the same person that did those actions, had those thoughts that I once was conscious of, though I have now forgot them? To which I answer, that we must here take notice what the word I is applied to; which, in this case, is the man only. [Essay II.xxvii.20]

Locke clearly has in mind that what constitutes the self at any given point in time is only those elements of memory that are available.   Those that are "beyond a possibility of retrieving them"are no longer part of the self.   Moreover, he does not suppose that our remembered experiences necessarily must consist of a continuous sequence stretching between any two events.   In a number of examples, he considers the possibility of the identical person spanning great stretches of time and space -- different bodies at different spatio-temporal locations.   So, given how "gappy"(in an objective temporal sense) our subjective memory of experiences is, given how fallible we know that memory is, and given how much we forget over time -- even barring "unusual"forms of amnesia -- what constitutes the Self in Locke's view is a small (and perhaps erroneous) part of the life we have lived.   (Especially if one considers valid tales of experiences from "prior lives".)

Locke's reliance on what person A remembers, at time t2, of experiences about some earlier time t1, poses grave consequences for both judicial (and ethical) assignments of responsibility, and the theological acknowledgement of the existence of Resurrectable persons.   Locke's memory based approach would entail an almost universal occurrence of multiple persons sequentially resident in any given body.   This would potentially pose a serious problem for his theory if one considers the significance of this consequence for the Resurrection -- would there be multiple versions of "John Locke"resurrected by God at the Resurrection?   Locke gets around this difficulty by supposing that at the Resurrection, God will ensure that memory recall of earlier experiences is both total and veridical.   Locke therefore considers the contribution only of "perfect"memory -- the memories that would be made available by God at the Resurrection.

If one rejects the theological aspects of Locke's philosophy, then his theory of personal identity would have been much better served if he had maintained instead that the best evidence for a continuity of consciousness consisted of instantaneous continuity of memory.   If at this instant, "I"remember sufficiently well what occurred at the immediately preceding instant, then that would constitute "instantaneous continuity"between the two instants.   This can be applied continuously forward and backward as far as necessary.   It would therefore become irrelevant whether I, now, could remember some experiences of "my"youth, if it could be reasoned that there existed a connected series of instants that demonstrated instantaneous continuity.   If Locke's theory of personal identity is corrected in this fashion (a rather minor correction, in the scheme of things), then many of the memory-focussed criticisms of his theory would be rendered null and void.

Finally, Locke's consciousness based theory of the identity of the self (even if corrected in the fashion just suggested) does not provide any answers for the questions raised by the "Duplicate Problem".   Suppose a Star Trek transporter accident resulted in a duplicate copy of me being created (say one copy gets transported, and the other copy gets bounced back to the transmitter).   Which of the duplicated versions is identical with the original?   Are they identical to each other?   There are a number of questions raised by this thought experiment that are not addressed by Locke's account of the self.   But the scenario creates difficulties for a number of different theories of personal identity, not just that of Locke.   So dealing with those questions will be left for another essay.


(1)   Locke, John (Author) & Yolton, John W. (Editor);   Essay Concerning Human Understanding, Everyman's Library, Dent Publishing, London England, 1961. ISBN: 0-460-00332-1.   All quotations from the Essay are cited as [Essay book.chapter.sub-section] of this edition.

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