... we might say that the earth has a spirit of growth; that its flesh is the soil, its bones the arrangement and connection of the rocks of which the mountains are composed, its cartilage the tufa, and its blood the springs of water.
Leonardo da VinciAnyone who conducts an argument by appealing to authority is not using his intelligence; he is just using his memory.
Leonardo da VinciNever 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 Vinci