Democritus

Combined the sensualism of Protagoras and the rationalism of the pre-Socratics; perception s yield opinions; reason gives knowlege of reality; reality consists in an infinite number of material atom-forms having primary qualities (form, inertia, etc.) and rearranging themselves in an infinite space; reason must abstract knowledge of them from the secondary qualities of perception (color, taste, etc.); reason is itself a product of matter in motion; mind-atoms are "hit" by images (small copies) of objects, giving rise to perception s from which scientific knowledge must be abstracted.