51 But you laugh at our reply, because, while we deny that souls are of royal descent, we do not, on the other hand, say in turn from what causes and beginnings they have sprung. But what kind of crime is it either to be ignorant of anything, or to confess quite openly that you do not know that of which you are ignorant? Or whether does he rather seem to you most deserving of ridicule who assumes to himself no knowledge of some dark subject; or he who thinks that he knows most clearly that which transcends human knowledge, and which has been involved in dark obscurity?
If the nature of everything were thoroughly considered, you too are in a position like that which you censure in our case. For you do not say anything which has been ascertained and set most clearly in the light of truth, because you say that souls descend from the Supreme Ruler Himself, and enter into the forms of men. For you conjecture, do not perceives this; surmise, do not actually know it; for if to know is to retain in the mind that which you have yourself seen or known, not one of those things which you affirm can you say that you have ever seen— that is, that souls descend from the abodes and regions above.
You are therefore making use of conjecture, not trusting clear information. But what is conjecture, except a doubtful imagining of things, and directing of the mind upon nothing accessible? He, then, who conjectures, does not comprehend, nor does he walk in the light of knowledge. But if this is true and certain in the opinion of proper and very wise judges, your conjectures, too, in which you trust, must be regarded as showing your ignorance.
Source: Against the Heathen (New Advent)