Scepticism is as much the result of knowledge as knowledge is of scepticism. To be content with what we at present know is for the most part to shut our ears against conviction; since from the very gra­dual character of our education we must continu­ally forget and emancipate ourselves from know­ledge previously acquired; we must set aside old notions and embrace fresh ones; and as we learn we must be daily unlearning something which it has cost us no small labour and anxiety to acquire