From Descartes' certain 'I think' to Locke's memory, Hume's bundle, the Buddhist denial of any self, and Parfit's claim that identity may not matter.
What am I — a thinking substance, a remembered continuity, a social construction, or no fixed thing at all?
Nothing is more familiar than being oneself, yet nothing is harder to catch in the act of examination. Descartes found the self the one thing that cannot be doubted; Locke relocated it from substance to remembered continuity; Hume, looking inward, could find no self at all, only a bundle of fleeting perceptions. Nineteenth-century thinkers made the self a task rather than a given — something achieved through freedom, recognition, or despair — while the Buddhist tradition had long insisted there is no abiding self to find. In the twentieth century the question turned practical and even numerical: if a person could be split or copied, what would happen to the self, and does personal identity ultimately matter as much as we assume? These positions disagree about whether the self is discovered, constructed, or dissolved.
Rationalism
Radical doubt leaves one thing standing: while I think, I cannot doubt that I exist — cogito, ergo sum. The self is thus known with certainty as a thinking thing before anything is known about the body or the external world. This 'I' is a simple, immaterial mental substance whose essence is thought, and it is the immovable point on which knowledge is rebuilt.
Discourse on Method (1637); Meditations on First Philosophy (1641).
Empiricism
Personal identity consists not in the sameness of soul or body but in continuity of consciousness — I am the same person as far back as I can extend my memory. A 'person' is a forensic, self-conscious being that can own its past acts, so the self is constituted by psychological continuity rather than an underlying substance. In principle the same self could inhabit different substances, and different selves the same substance.
An Essay Concerning Human Understanding (1689), II.27, 'Of Identity and Diversity'.
Empiricism
When I enter most intimately into what I call myself, I stumble only on particular perceptions and never catch a self without them. The self is therefore a 'bundle of perceptions' in perpetual flux, and belief in a simple, continuing identity is a fiction produced by memory and the imagination's habit of associating related impressions. Personal identity is a grammatical convenience, not a metaphysical fact.
A Treatise of Human Nature (1739–40), 'Of Personal Identity'.
German idealism / critical philosophy
The 'I think' must be able to accompany all my representations — this transcendental unity of apperception is the formal condition of any experience, not itself an object of experience. We know the self only as it appears in inner sense, never the self as it is in itself, so Hume was right that no self-substance is given and Descartes wrong to think the cogito yields metaphysical knowledge. The self is the unifying activity presupposed by knowledge, not a thing found within it.
Critique of Pure Reason (1781/1787), 'Transcendental Deduction' and 'Paralogisms'.
German idealism
The self (the 'I') is not a given thing but an original act — it posits itself, and in the same stroke posits a not-self against which it can act. Selfhood is fundamentally practical: the I is self-positing activity and freedom, striving against the limits it sets for itself. There is no substance behind this deed; the self simply is the ceaseless activity of self-constitution.
Foundations of the Science of Knowledge (Wissenschaftslehre, 1794).
German idealism
Self-consciousness is not a solitary given but is achieved only through recognition by another self-consciousness — 'I' becomes fully itself only in a 'we'. The famous master–slave dialectic shows the self forming through conflict, labour, and mutual acknowledgement rather than by inward inspection. The self is thus social and historical, realized in institutions and in the movement of Spirit, not a private inner point.
Phenomenology of Spirit (1807), 'Self-Consciousness'.
Existentialism (Christian)
'The self is a relation that relates itself to itself' — a synthesis of finite and infinite, necessity and possibility, that must be actively held together. Selfhood is a task and an achievement, not a fact; failure to become a self, or to ground it transparently in the power that established it, is despair, 'the sickness unto death'. To be a self is to choose oneself before God in inward passion.
The Sickness unto Death (1849); Either/Or (1843).
Pragmatism / psychology
James distinguishes the 'I' (the knowing self, the passing thought) from the 'Me' (the self as known — material, social, and spiritual). A person 'has as many social selves as there are individuals who recognize him', and the sense of personal identity is carried by the ongoing stream of consciousness appropriating its own past. The self is a functional process of feeling and appropriating, not a fixed metaphysical soul.
The Principles of Psychology (1890), ch. 10, 'The Consciousness of Self'.
Madhyamaka Buddhism
There is no independently existing self; the person, like everything else, is 'empty' (śūnya) of intrinsic nature, arising only in dependence on conditions. The self is neither identical with the aggregates nor different from them, neither existent nor simply non-existent — all such positions are refuted. Recognizing the self's emptiness is not nihilism but liberation from the grasping that emptiness exposes as baseless.
Mūlamadhyamakakārikā (Fundamental Verses on the Middle Way).
Existentialism
Consciousness (being-for-itself) has no fixed self or essence at its core; the ego is not the owner but the product of consciousness, an object it constitutes. Because existence precedes essence, the self is not something one is but something one perpetually makes through free choice, and to treat it as a fixed thing is 'bad faith'. The 'look' of the Other, moreover, discloses a dimension of the self I cannot control.
The Transcendence of the Ego (1936); Being and Nothingness (1943).
Hermeneutics / phenomenology
Ricoeur distinguishes 'sameness' (idem, what stays constant) from 'selfhood' (ipse, who keeps one's word and answers 'here I am'), and argues that the self is constituted narratively. We know who we are by telling the story that binds our scattered life into a plot, mediated by others and by the texts and traditions we inherit. The self is thus an interpretive achievement, at once mine and irreducibly relational.
Oneself as Another (Soi-même comme un autre, 1990).
Analytic philosophy
Personal identity is not what matters: what matters is psychological continuity and connectedness (Relation R), which could in principle hold to varying degrees or branch to more than one future person. Thought experiments about teleportation and brain-splitting show that questions like 'will that future person be me?' can be empty. This 'reductionist' view, Parfit held, is liberating — it loosens the grip of self-concern and brings ethics closer to a wider impartiality.
Reasons and Persons (1984), Part III.