By convention sweet is sweet, by convention bitter is bitter, by convention hot is hot, by convention cold is cold, by convention color is color. But in reality there are atoms and the void. That is, the objects of sense are supposed to be real and it is customary to regard them as such, but in truth they are not. Only the atoms and the void are real.

[νόμωι (γάρ φησι) γλυκὺ καὶ νόμωι πικρόν, νόμωι θερμόν, νόμωι ψυχρόν, νόμωι χροιή, ἐτεῆι δὲ ἄτομα καὶ κενόν]

Democritus (c. 460 BC - c. 370 BC) Greek philosopher

Frag. 0 (Diels) [tr. Bakewell (1907)]
    (Source)

Cited to Tetralogies of Thrasyllus, 9; Sext. Emp. Math VII 135. Alternate translations:

• "Sweet exists by convention, bitter by convention, colour by convention; atoms and Void (alone) exist in reality ... We know nothing accurately in reality, but (only) as it changes according to the bodily condition, and the constitution of those things that flow upon (the body) and impinge upon it." [tr. Freeman (1948), frag. 9]
• "By convention sweet is sweet, bitter is bitter, hot is hot, cold is cold, color is color; but in truth there are only atoms and the void." [tr. Durant, from Bakewell]