The certainty of Reid's philosophical instinct, if such an expression be allowed, and at the same time his tragic limitations, due to an inability fully to understand the origin of this instinct, come out clearly in the battle he waged against the 'idea' as his immediate predecessors understood it. We know that Plato introduced this word into the philosophical language of mankind. In Greek ιδέα (from ιδεá¿Î½, to see) means something of which one knows that it exists, because one sees it. It was therefore possible to use the word 'to see' as Plato did, because in his day it covered both sensible and supersensible perception. For Plato, knowing consisted in the soul's raising itself to perceiving the objective, world-forming IDEAS, and this action comprised at the same time a recollection of what the soul had seen while it lived, as an Idea among Ideas, before its appearance on earth.