Let us consider this question more precisely. Is there any self-existent fire ? and do all those things which we call self-existent exist ? or are only those things which we see, or in some way perceive through the bodily organs, truly existent, and nothing whatever besides them ? And is all that which, we call an intelligible essence nothing at all, and only a name ? Here is a question which we must not leave unexamined or undetermined, nor must we affirm too confidently that there can be no decision ; neither must we interpolate in our present long discourse a digression equally long, but if it is possible to set forth a great principle in a few words, that is just what we want.
Thus I state my view : — If mind and true opinion are two distinct classes, then I say that there certainly are these self-existent ideas unperceived by sense, and apprehended only by the mind ; if, however, as some say, true opinion differs in no respect from mind, then everything that we perceive through the body is to be regarded as most real and certain. But we must affirm that to be distinct, for they have a distinct origin and are of a different nature ; the one is implanted in us by instruction, the other by persuasion ; the one is always accompanied by true reason, the other is without reason ; the one cannot be overcome by persuasion, but the other can : and lastly, every man may be said to share in true opinion, but mind is the attribute of the gods and of very few men.