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

Philosophy is written in that great book which ever lies 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.

It reveals to me the causes of many natural phenomena that are entirely incomprehensible in the light of the generally accepted hypotheses. To refute the latter I collected many proofs, but I do not publish them ... I would dare to publish my speculations if there were people men like you.

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.

I am inclined to think that the authority of Holy Scripture is intended to convince men of those truths which are necessary for their salvation, which, being far above man's understanding, can not be made credible by any learning, or any other means than revelation by the Holy Spirit.

Alas! Your dear friend and servant Galileo has been for the last month hopelessly blind; so that this heaven, this earth, this universe, which I by my marvelous discoveries and clear demonstrations had enlarged a hundred thousand times beyond the belief of the wise men of bygone ages, henceforward for me is shrunk into such a small space as is filled by my own bodily sensations.

It is surely harmful to souls to make it a heresy to believe what is proved.