Republic

That is. How could that which is not be known? We are sufficiently assured of this, then, even if we should examine it from every point of view, that that which entirelyis is entirely knowable, and that which in no way is is in every way unknowable. Most sufficiently. Good. If a thing, then, is so conditioned as both to be and not to be, would it not lie between that which absolutely and unqualifiedly is and that which in no way is? Between. Then if knowledge pertains to that which is and ignorance of necessity to that which is not, for that which lies between we must seek for something between nescience and science, if such a thing there be. By all means. Is there a thing which we call opinion? Surely. Is it a different faculty from science or the same? A different. Then opinion is set over one thing and science over another, each by virtue of its own distinctive power or faculty. That is so. May we say, then, that science is naturally related to that which is, to know that and how that which is is? But rather, before we proceed, I think we must draw the following distinctions. What ones? Shall we say that faculties, powers, abilities are a class of entities by virtue of which we and all other things are able to do what we or they are able to do? I mean that sight and hearing, for example, are faculties, if so be that you understand the class or type that I am trying to describe. I understand, he said. Hear, then, my notion about them. In a faculty I cannot see any color or shape or similar mark such as those on which in many other cases I fix my eyes in discriminating in my thought one thing from another. But in the case of a faculty I look to one thing only—that to which it is related and what it effects, and it is in this way that I come to call each one of them a faculty, and that which is related to the same thing and accomplishes the same thing I call the same faculty, and that to another I call other. How about you, what is your practice? The same, he said. To return, then, my friend, said I, to science or true knowledge, do you say that it is a faculty and a power, or in what class do you put it? Into this, he said, the most potent of all faculties. And opinion—shall we assign it to some other class than faculty. By no means, he said, for that by which we are able to opine is nothing else than the faculty of opinion. But not long ago you agreed that science and opinion are not identical. How could any rational man affirm the identity of the infallible with the fallible?