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Locke's Psychology of Personal Identity
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Journal of the History of Philosophy 38.1 (2000) 41-61

Raymond Martin

University of Maryland


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.

Locke's theory of personal identity is a subtle blend of conceptual analysis, metaphysics, and psychology. The conceptual analysis and metaphysics have been discussed repeatedly. The psychology has been relatively ignored. Yet, by just attending to Locke's conceptual analysis and metaphysics, one can know that, in Locke's view, consciousness—via memory—unifies persons over time, but not how consciousness unifies persons, either over time or at a time; nor can one know why, for Locke, the mechanics of self-constitution is crucially important to personal identity. In my opinion, to understand Locke's theory and its impact on subsequent eighteenth-century thought, one must understand how, in Locke's approach, analysis, metaphysics, and psychology are interrelated. However, in the present paper I simply explain Locke's neglected thoughts on the psychology of personal identity, in the end, adding a few words—very few—about their historical and contemporary importance.

2. Inanimate and Animate Objects

Ignoring artifacts, for the moment, Locke proposed separate accounts of the identity conditions for inanimate objects, animate objects, and persons. In the case of inanimate objects, an individual at one time and one at another are the same just if they are composed of exactly the same matter. For instance, a collection of sand grains remains the same collection even if the grains are rearranged, so long as the collection does neither gains or loses a grain. In the case of plants and animals, an individual at one time and one at another are the same just if they both have a kind of shape appropriate to that sort of plant or animal and both sustain the same life. In Locke's view, the shape of an animal, not its mentality, determines what biological kind of thing it is. Unless one recognizes this, he thought, one might be tempted to say of a rational parrot, if there were one, that it is human. In addition, in Locke's view, the life of a thing is simply a way in which its (perhaps exclusively) material parts are organized so as to promote its functioning in a manner appropriate to the sort of thing it is. And a plant or animal can so function, that is, maintain its life, even if the matter (and/or spirit) out of which it is composed at any given time is replaced by different matter (and/or spirit). In sum, still leaving artifacts to one side, Locke's view was that, whereas in the case of inanimate objects, composition but not organization matters, in the case of animate objects, shape and organization, but not composition or mentality matters. In the case of artifacts, Locke acknowledged the importance of function and allowed for replacement of matter. But he did this not in his chapter on identity and not systematically, but scattered throughout the Essay (e.g., II.6.41: 465.05; III.6.40: 464.25).

3. Persons

In the case of persons, Locke is unequivocal. Although biological kind, in virtue of its relation to shape and life, is essential to humanhood, it is not essential topersonhood; rather, consciousness and only consciousness matters. In Locke's view, a rational parrot could not be human and, hence, a fortiori, could not be the same human as an individual at some other time. But a rational parrot could be the same person as an individual at some other time. This much about Locke's view of persons is clear. Almost everything else about it is unclear.

On one interpretation of the rest of Locke's account, an individual at one time and one at another are the same person just if the individual at the later time is conscious of having experienced or done what the individual at the earlier time experienced or did. On what is possibly another interpretation, an additional requirement is...

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