Quality / Quantity — Central Aristotelian categories. Quality (ποιόν) is what something is in a certain way — white, hot, virtuous. Quantity (ποσόν) is how much something is — number, extension, duration. In Modernity, Galileo and Descartes distinguish primary qualities (extension, figure, motion — objective, real in the object) from secondary qualities (color, smell, taste — subjective, observer-dependent). Locke systematizes this distinction, which dominates classical physics and opens debate on the nature of perception.
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