When men are arrived at the goal, they should not turn back.

Let us carefully observe those good qualities wherein our enemies excel us; and endeavor to excel them, by avoiding what is faulty, and imitating what is excellent in them.

What sort of tree is there which will not, if neglected, grow crooked and unfruitful; what but Will, if rightly ordered, prove productive and bring its fruit to maturity? What strength of body is there which will not lose its vigor and fall to decay by laziness, nice usage, and debauchery?

What most of all enables a man to serve the public is not wealth, but content and independence; which, requiring no superfluity at home, distracts not the mind from the common good.

The process may seem strange and yet it is very true. I did not so much gain the knowledge of things by the words, as words by the experience I had of things.

It is a thing of no great difficulty to raise objections against another man's oration, it is a very easy matter; but to produce a better in it's place is a work extremely troublesome.

This excerpt is presented as reproduced by Copernicus in the preface to De Revolutionibus: "Some think that the earth remains at rest. But Philolaus the Pythagorean believes that, like the sun and moon, it revolves around the fire in an oblique circle. Heraclides of Pontus and Ecphantus the Pythagorean make the earth move, not in a progressive motion, but like a wheel in rotation from west to east around its own center."