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How did Democritus explain sensations such as sweetness and bitterness?

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Bronze bust of Epicurus with a full beard and draped clothing, displayed on a round inscribed base at the National Archaeological Museum of Naples. — Atomism Epicurus, bronze bust from a Greek original, c. 280–270 bce; in the Museo Archeologico Nazionale, Naples.

Democritus explained sensations such as sweetness and bitterness by asserting that they are not inherent qualities of the atoms themselves, but rather subjective impressions produced in the soul by the physical interaction of atoms.1

According to his atomic theory, atoms possess only quantitative properties—specifically shape, size, arrangement, and position. Sensations arise when atoms emitted from objects impinge upon the soul. Because these sensations are merely effects caused by the configuration of atoms, Democritus argued that qualities like sweetness or bitterness exist only by convention; in reality, only atoms and the void exist.12

For example, he specifically attributed the sensation of a sweet taste to the presence of round and not excessively small atoms. Conversely, other sensations are determined by different geometric properties, such as the roughness or smoothness of the atoms involved.1