Full Idea
Sweet exists by convention, bitter by convention, colour by convention; atoms and void alone exist in reality.
Clarification
'Convention' is the Greek word 'nomos', which also translates as 'law'
Gist of Idea
Experiences are merely convention; only atoms and the void are real
Source
Democritus (fragments/reports [c.431 BCE], B009), quoted by Sextus Empiricus - Against the Logicians (two books) 7.135
Book Reference
'Ancilla to the Pre-Socratic Philosophers', ed/tr. Freeman,Kathleen [Harvard 1957], p.93