Identity of Persons

In eighteenth-century Britain, the most important treatment of the topic is by David Hume (1711–1776) in a famous section of his Treatise of Human Nature (1739). Hume rejects the traditional Cartesian view, arguing that through inner experience one can identify only a variety (a "bundle") of distinct perceptions; there is no experiential evidence of a soul that remains the same through time. Hume recognizes, however, that we nevertheless have a "natural propension" to ascribe unity and identity to the self. He argues that the idea of a unitary and identical mind is to the result of the imagination's connecting successive ideas in such a way as to create the belief that there is an identical self to which all these ideas belong. In the appendix to the Treatise Hume reflects critically on his own discussion of personal identity, relating the problem to his earlier explanation of "the principle of connexion" that "makes us attribute" identity to the mind. But Hume still holds that inner experience and observation reveal only collections or "bundles" of perceptions and that we nevertheless have a "natural propension" to ascribe identity to the self. Hume has mostly been read as reducing the self to its experiences or perceptions and as denying the existence of an essential self beyond the perceptions; but this reading has been criticized in recent commentary. While most eighteenth-century materialist thinkers simply adopted the Lockean view about personal identity, some (Michael Hissmann, Thomas Cooper) started from a Humean position but explicitly argued, unlike Hume, that there is no such a thing as personal identity at all.

Immanuel Kant's (1724–1804) approach, however, is different in kind from previous theories, as he was not concerned with empirical personal identity. Although Kant commented on empirical questions in some places, he did so in the light of his important distinction between empirical and what he calls "pure" or "transcendental" self-consciousness, or apperception, in the Critique of Pure Reason (1781). Unity and identity of self-consciousness are required for any thought to be possible at all. The identity of transcendental self-consciousness is "original" because it "precedes a priori all my determinate thought." Empirical consciousness, by contrast, "is in itself diverse and without relation to the identity of the subject." Kant makes use of this distinction in his critique of traditional rationalist metaphysics of the self or soul, known as "rational psychology." Its aim, according to Kant, is to show by way of a priori reasoning that (among other things) the self is a simple substance or soul and numerically identical at different points of time. But he argues that even the substantiality of the soul could not be inferred from the consciousness that I am the subject of all my thoughts. For knowledge of objects, including knowledge of the self as object, requires experience. In his moral philosophy Kant distinguished moral personality from both the empirical and the transcendental self and attempted to show that the idea of moral-practical freedom of the self has objective reality. In German idealism, too, the issue of empirical personal identity through time was not a major concern. However, both Kantian and empiricist examinations of consciousness and identity continued to appear simultaneously with the speculations of the idealists.