PHIL 110 · Metaphysics — Identity and Persistence Through Time

Led by Leibniz

The fifth module of the Cambridge Part IA Metaphysics paper, led by Leibniz. What is it for a thing to be one and the same — at a moment, and across time? Leibniz gives the two principles that bear his name, defends the bold claim that no two things are exactly alike, and confronts the Ship of Theseus, the rival pictures of endurance and perdurance, and the question that matters most: what makes you the same person over a lifetime?

1. Module 5 ○ Open

   Identity and Persistence Through Time

   Led by Leibniz

   The question

   What makes something one and the same thing — and what makes it the same thing *still*, after it has changed? Leibniz separates being numerically one from being merely alike, and offers two principles: that identical things must share every property, and, more boldly, that things sharing every property must be identical — so that the world never exactly repeats itself. The module then turns to persistence: how the ship survives the replacement of all its planks (and what happens when the old planks are rebuilt into a second ship), whether a thing lasts by being wholly present at each moment or by having parts spread through time, and — the case that matters most — what makes you the same person as the child you were and the person you will be tomorrow.

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