An Essay Concerning Human Understanding
John Locke · 1689
"The mind at birth is a blank slate, tabula rasa, with no innate ideas — all knowledge, without exception, is built up from sensory experience and the mind's reflection on that experience."
Locke's Essay was a direct attack on the then-dominant rationalist view that some ideas, of God, of logic, of morality, are innate, built into the mind before any experience. His alternative: the mind starts as a blank slate, and every idea, no matter how abstract, can ultimately be traced back to either sensation, direct input from the external world through the senses, or reflection, the mind's own operations on those sensory ideas, like combining, comparing, or abstracting them.
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Meditations on First Philosophy
"By systematically doubting everything that can possibly be doubted, including the reliability of the senses, Descartes arrives at one thing that survives the doubt — the fact that he is thinking, and therefore exists, cogito ergo sum — and builds all further certain knowledge back up from that single indubitable foundation using reason alone."