One afternoon, ca 440 BC, Leucippus and Democritus were sitting on their tripods doing bong rips (Leucippus had scored it from his Scythian dealer), when Democritus said:

Democritus: Dude, like sweet is just whatever people say is sweet, and the same goes for bitter, and we get taught which is hot and which is cold and which colours are which, but have you ever thought about ... like ... it could be that that's all in our heads, man ... y'know in reality, there's like nothing but atoms; atoms and void between them.

Leucippus: Woah