Many Western thinkers followed his lead. Rationalist philosopher René
Descartes (1596–1650) explained that I am I because I think (cogito ergo sum, in
Latin, the language in which he wrote). Being endowed with reason was for him
what allows me to say that I exist. John Locke (1632–1704) changed the focus
slightly. In addition to rationality, he emphasized a specific kind of self-
knowledge, personal memory, as a necessary condition of individual identity.
Gottfried Wilhelm Leibniz (1646–1716) thought that the world consisted of
infinitely many substances, each located at a point in space, some of which—
human minds—were gifted with reason. Because all of these substances, which
Leibniz called ‘monads’, were strictly distinct, everything could be identical just
with itself. Georg W. F. Hegel (1770–1831) continued the rationalist tradition of
accentuating consciousness as the basis of the individual self. And a century
later, Ernst Cassirer still called autognosis the supreme purpose of philosophical
inquiry.
The question of how consciousness and self-awareness connect with personal
identity has accompanied philosophy since antiquity. Sages of diverse
orientations have put forth various elaborate answers, showing among other
things that self-awareness is more than just being conscious. Yet, it seems a self-
sustaining pursuit, producing new puzzles with every solution. That individual
identity means being a rational creature with a personal memory is not the end of
the story.
I forgot
I still can’t remember, but I know there was something I meant to say. Who
forgot, and who knows that there was something? Is that the same I or two parts
of myself? What was her name again? It begins with an L and has three
syllables. No, it wasn’t Lolita. Wait, it’ll come back to me—but where from? Is
my true self the one who forgot or the one who is looking for the three-syllable
name, confident of retrieving it; and if so, where does he look if not inside me?
Two related problems arise here: the first concerns identity through time, the
second the mind–body problem.
The metaphysics of change already occupied Presocratic thinkers. Parmenides
(515–445 BCE) taught, ‘there is nothing new under the sun’. The eternal laws of
logic make it impossible for something to both exist and not exist, which