The Grand Duke [of Tuscany] ...after observing the Medicaean plants several times with me ... has now invited me to attach myself to him with the annual salary of one thousand florins, and with the title of Philosopher and Principal Mathematicial to His Highness; without the duties of office to perform, but with the most complete leisure; so that I can complete my Treatises.

I believe that the intention of Holy Writ was to persuade men of the truths necessary to salvation; such as neither science nor other means could render credible, but only the voice of the Holy Spirit.

The Divine intellect indeed knows infinitely more propositions [than we can ever know]. But with regard to those few which the human intellect does understand, I believe that its knowledge equals the Divine in objective certainty.

One can understand nature only when one has learned the language and the signs in which it speaks to us; but this language is mathematics and these signs are methematical figures.

Some, merely to contradict what I had said, did not scruple to cast doubt upon things they had seen with their own eyes again and again.

I would say here something that was heard from an ecclesiastic of the most eminent degree: The intention of the Holy Spirit is to teach us how one goes to heaven, not how the heavens go.

Nature . . . is inexorable and immutable; she never transgresses the laws imposed upon her, nor cares a whit whether her abstruse reasons and methods of operations are understandable to men.