For we come into the world having by nature no idea of a right-angled triangle or of a quarter-tone, or of a semi-tone,but by a certain tradition of art we learn each of these things. And thus those who know them not, do not suppose that they know them. But good and evil, and nobleness and baseness, and the seemly and the unseemly, and happi ness and misfortune, and what is our concern and what is not, and what ought to be done and what not — who has come into the world without an im planted notion of these things Thus we all use these terms, and endeavour to fit our natural conceptions to every several thing. Behold, the beginning of philosophy is the observation of how men contradict one another, and the search whence comes this contradiction, and the censure and mistrust of bare opinion. And it is an inquiry into that which seems, whether it rightly seems; and the discovery of a certain rule, even as we have found a balance for weights and a plumb linefor straight and crooked. This is the beginning of philosophy. Are all things right to all to whom they seem so? But how can contradictory things be right?