“Painting for me is like a fabric, all of a piece and uniform, with one set of threads as the representational, esthetic element, and the cross-threads as the technical, architectural, or abstract element. These threads are interdependent and complementary, and if one set is lacking the fabric does not exist.A picture with no representational purpose is to my mind always an incomplete technical exercise, for the only purpose of any picture is to achieve representation.”

The Notebooks of Leonardo da Vinci (1883), IX The Practice of Painting
Context: 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.

Zachman (1986) as cited in: Peter Bernus, Kai Mertins, Günter Schmidt (2005) Handbook on Architectures of Information Systems. p. 544

Source: The Character of Physical Law (1965), chapter 1, “The Law of Gravitation,” p. 34

"Notes on Abstract Art" in Herbert Read's Ben Nicholson: Paintings, Reliefs, Drawings (London, 1948)

Source: Xenocide

Source: Why Stock Markets Crash - Critical Events in Complex Systems (2003), Chapter 5, Modeling Financial Bubbles And Market Crashes, p. 134.

Essay on the Theory of Painting (1725)

Letter Three (23 April 1903)
Letters to a Young Poet (1934)