To know that we know what we know, and to know that we do not know what we do not know, that is true knowledge.

If there be some who, though ignorant of all mathematics . . . dare to reprove this work, because of some passage of Scripture, which they have miserably warped to their purpose, I regard them not, and even despise their rash judgement.

Finally we shall place the Sun himself at the center of the Universe.

To know that we know what we know, and to know that we do not know what we do not know, that is true knowledge.

For it is the duty of an astronomer to compose the history of the celestial motions through careful and expert study.

Although all the good arts serve to draw man's mind away from vices and lead it toward better things, this function can be more fully performed by this art, which also provides extraordinary intellectual pleasure.

Accordingly, since nothing prevents the earth from moving, I suggest that we should now consider also whether several motions suit it, so that it can be regarded as one of the planets. For, it is not the center of all the revolutions.