But it is of Plato after all we should be thinking; of the comparatively temperate thoughts, the axiomata media, he was able to derive, by a [43] sort of compromise, from the impossible paradox of his ancient master. What was it, among things inevitably manifest on his pages as we read him, that Plato borrowed and kept from the Eleatic School!
Two essential judgments of his philosophy: The opposition of what is, to what appears; and the parallel opposition of knowledge to opinion; (heteron epistêmês doxa; eph' heterô ara heteron ti dynamenê hekatera autôn pephyke? ouk enchôrei gnôston kai doxaston tauton einai?)+ and thirdly, to illustrate that opposition, the figurative use, so impressed on thought and speech by Plato that it has come to seem hardly a figure of speech at all but appropriate philosophic language, of the opposition of light to darkness.—
Well, then (Socrates is made to say in the fifth book of The Republic) if what is, is the object of knowledge, would not something other than what is, be the object of opinion?
Yes! something else.
Does opinion then opine what is not; or is it impossible to have even opinion concerning what is not? Consider! does not he who has opinion direct his opinion upon something? or is it impossible, again, to have an opinion, yet an opinion about nothing?
Impossible!
But he who has an opinion has opinion at least about something; hasn't he? Yet after all what is not, is not a thing; but would most properly be denominated nothing.
Certainly.
Now to what is not, we assigned of necessity ignorance: to what is, knowledge.
Rightly: he said.