We do not ask what hope of gain makes a little bird warble, since we know that it takes delight in singing because it is for that very singing that the bird was made, so there is no need to ask why the human mind undertakes such toil in seeking out these secrets of the heavens. ... And just as other animals, and the human body, are sustained by food and drink, so the very spirit of Man, which is something distinct from Man, is nourished, is increased, and in a sense grows up on this diet of knowledge, and is more like the dead than the living if it is touched by no desire for these things.

The Earth is round, and is inhabited on all sides, is insignificantly small, and is borne through the stars.

Some of what these pamphlets [of astrological forecasts] say will turn out to be true, but most of it time and experience will expose as empty and worthless. The latter part will be forgotten literally: written on the winds while the former will be carefully entered in people's memories, as is usual with the crowd.

The squares of the periodic times are proportional to the cubes of the mean distances from the sun.

The wisdom of the Lord is infinite as are also His glory and His power. Ye heavens, sing His praises; sun, moon, and planets, glorify Him in your ineffable language! Praise Him, celestial harmonies, and all ye who can comprehend them! And thou, my soul, praise thy Creator! It is by Him and in Him that all exist.

In theology we must consider the predominance of authority; in philosophy the predominance of reason.

When ships to sail the void between the stars have been built, there will step forth men to sail these ships.