A bird is an instrument working according to mathematical law, which instrument it is within the capacity of man to reproduce with all its movements, but not with a corresponding degree of strength, though it is deficient only in the power of maintaining equilibrium. We may therefore say that such an instrument constructed by man is lacking in nothing except the life of the bird, and this life must needs be supplied from that of man.
Leonardo da VinciThough I may not . . . be able to quote other authors, I shall rely on that which is much greater and more worthy - on experience.
Leonardo da VinciOysters open completely when the moon is full; and when the crab sees one it throws a piece of stone or seaweed into it and the oyster cannot close again so that it serves the crab for meat. Such is the fate of him who opens his mouth too much and thereby puts himself at the mercy of the listener.
Leonardo da VinciAnyone who conducts an argument by appealing to authority is not using his intelligence; he is just using his memory.
Leonardo da Vinci