“Does the painter imitate the body correctly if he guides his brush without any method, and if his hand is moved at random and the lines are not drawn with art? In the same way you will not put the sentiment of your mind in front of the others’ eyes unless you use appropriate and distinct words, a fitting arrangement of words and the right order of sentences. For, just as we represent bodies by colours, we represent the sentiment of our mind by speech.”

Source: The Omnivore's Dilemma: A Natural History of Four Meals

The lecture in Ashland, Oregon (8th of July 2005)

Speech to the Virginia Convention (1861)
Context: These are pregnant statements; they avow a sentiment, a political principle of action, a sentiment of hatred to slavery as extreme as hatred can exist. The political principle here avowed is, that his action against slavery is not to be restrained by the Constitution of the United States, as interpreted by the Supreme Court of the United States. I say, if you can find any degree of hatred greater than that, I should like to see it. This is the sentiment of the chosen leader of the Black Republican party; and can you doubt that it is not entertained by every solitary member of that same party? You cannot, I think. He is a representative man; his sentiments are the sentiments of his party; his principles of political action are the principles of political action of his party. I say, then; it is true, at least, that the Republican party of the North hates slavery.

Source: 1961 - 1975, Art Talk, conversations with 15 woman artists', (1975), p. 21

VII. On the Nature of the World and its Eternity.
On the Gods and the Cosmos

Pearls of Wisdom

[tr. Elizabeth Carter]
Alternative translation: If someone turned your body over to just any person who happened to meet you, you would be angry. But are you not ashamed that you turn over your own faculty of judgment to whoever happens along, so that if he abuses you it is upset and confused? (28) http://books.google.com/books?id=9WRzxtTBkPgC&lpg=PA19&ots=hXwTf1JmW6&dq=%22'If%20someone%20turned%20your%20body%20over%20to%20just%20any%20person%20who%20happened%20to%20meet%20you%2C%20you%20would%20be%20angry.%22&pg=PA19#v=onepage&q&f=false tr. Nicholas P. White
The Enchiridion (c. 135)

a passage Martin wrote in 1975 'On a Clear Day', 15 Oct. 1975. Printed in Agnes Martin, eds. Morris and Bell, p. 124
1970's

In 'Beauty Is the Mystery of Life', 1989; a lecture by Agnes Martin, Carnegie Museum of Art, Pittsburgh, 1989. Printed in Agnes Martin, eds. Morris and Bell, pp. 158–59
1980 - 2000