I think that in the discussion of natural problems we ought to begin not with the Scriptures, but with experiments, and demonstrations.

Nature...does not act by means of many things when it can do so by means of a few.

The laws of Nature are written in the language of mathematics...the symbols are triangles, circles and other geometrical figures, without whose help it is impossible to comprehend a single word.

It has always seemed to me extreme presumptuousness on the part of those who want to make human ability the measure of what nature can and knows how to do, since, when one comes down to it, there is not one effect in nature, no matter how small, that even the most speculative minds can fully understand.

It was granted to me alone to discover all the new phenomena in the sky and nothing to anybody else. This is the truth which neither envy nor malice can supress.

But, because my private lectures and domestic pupils are a great hinderance and intteruption of my studies, I wish to live entirely exempt from the former, and in great measure from the latter. ... in short, I should wish to gain my bread from my writings.

I wish, my dear Kepler, that we could have a good laugh together at the extraordinary stupidity of the mob. What do you think of the foremost philosophers of this University? In spite of my oft-repeated efforts and invitations, they have refused, with the obstinacy of a glutted adder, to look at the planets or the Moon or my glass [telescope].