Never make heads straight on the shoulders, but turn them aside to the right or to the left, even though they look down, or upward, or straight ahead, because it is necessary for them to look lively and awake and not asleep. And do not depict the front or rear half of the whole person so that too much straightness is displaced, one half above or below the other half; and if you should wish to use stiff figures, do so only in portraying old people.
Leonardo da VinciAfter painting comes Sculpture, a very noble art, but one that does not in the execution require the same supreme ingenuity as the art of painting, since in two most important and difficult particulars, in foreshortening and in light and shade, for which the painter has to invent a process, sculpture is helped by nature. Moreover, Sculpture does not imitate color which the painter takes pains to attune so that the shadows accompany the lights.
Leonardo da VinciThe lover is moved by the beloved object as the senses are by sensual objects; and they unite and become one and the same thing. The work is the first thing born of this union; if the thing loved is base the lover becomes base.
Leonardo da VinciA bird maintains itself in the air by imperceptible balancing, when near to the mountains or lofty ocean crags; it does this by means of the curves of the winds which as they strike against these projections, being forced to preserve their first impetus bend their straight course towards the sky with divers revolutions, at the beginning of which the birds come to a stop with their wings open, receiving underneath themselves the continual buffetings of the reflex courses of the winds.
Leonardo da Vinci