Knowing thyself, that is the greatest wisdom.

Philosophy [nature] is written in that great book which ever is before our eyes -- I mean the universe -- but we cannot understand it if we do not first learn the language and grasp the symbols in which it is written. The book is written in mathematical language, and the symbols are triangles, circles and other geometrical figures, without whose help it is impossible to comprehend a single word of it; without which one wanders in vain through a dark labyrinth.

With regard to matters requiring thought: the less people know and understand about them, the more positively they attempt to argue concerning them.

For my part I consider the earth very noble and admirable precisely because of the diverse alterations, changes, generations, etc. that occur in it incessantly.

To be humane, we must ever be ready to pronounce that wise, ingenious and modest statement 'I do not know'.

It is a beautiful and delightful sight to behold the body of the Moon.

But some, besides allegiance to their original error, possess I know not what fanciful interest in remaining hostile not so much toward the things in question as toward their discoverer.