A picture or representation of human figures, ought to be done in such a way as that the spectator may easily recognise, by means of their attitudes, the purpose in their minds. Thus, if you have to represent a man of noble character in the act of speaking, let his gestures be such as naturally accompany good words; and, in the same way, if you wish to depict a man of a brutal nature, give him fierce movements; as with his arms flung out towards the listener, and his head and breast thrust forward beyond his feet, as if following the speaker’s hands. Thus it is with a deaf and dumb person who, when he sees two men in conversation—although he is deprived of hearing—can nevertheless understand, from the attitudes and gestures of the speakers, the nature of their discussion. I once saw in Florence a man who had become deaf who, when you spoke very loud did not understand you, but if you spoke gently and without making any sound, understood merely from the movement of the lips. Now perhaps you will say that the lips of a man who speaks loudly do not move like those of one speaking softly, and that if they were to move them alike they would be alike understood. As to this argument, I leave the decision to experiment; make a man speak to you gently and note [the motion of] his lips.
[Footnote: The first ten lines of this text have already been published, but with a slightly different reading by Dr. M. JORDAN: Das Malerbuch Leonardo da Vinci’s p. 86.]
Taken from The Notebooks of Leonardo da Vinci edited by Jean Paul Richter, 1880.