Because, my good friend, even if we find someone who professes knowledge of the art of demonstration and the ability to teach it to another, we shall not, I fancy, believe him at once, but look for someone else who can determine if the first man is speaking the truth. And even if we find this one, we are still not clear whether our arbiter knows how to distinguish the man whose judgment is correct or not, and for him too I fancy we shall need another arbiter. For how could we ourselves know how to choose the one able to judge best? Do you see how this goes on to infinity and cannot stop and be arrested? For you will see that all the proofs you can find are disputable and have no certainty. Most of them try to compel our belief on a basis of assumptions equally open to dispute, while the rest tack the most obscure and quite unrelated speculations on to self-evident truths and then say that the latter prove the former, as if a man thought to prove the existence of gods because we see their altars. So, Hermotimus, we seem to have run round in a circle and come back to our starting-point and the self-same difficulty.