A candle melts beyond recognition, yet Descartes says you still know it's the same wax

Every sensible quality of a piece of wax — its shape, smell, hardness, sound — changes completely once it melts near a flame, yet you're certain it's still the same wax. Descartes argued this certainty can't come from the senses or imagination, since those qualities are gone; it must come from the intellect alone, judging what the wax is capable of becoming.

— René Descartes, Meditations on First Philosophy — Second Meditation, 1641
Go deeper: get the book →