I am fully conscious that, not being a literary man , certain presumptuous persons will think that they may reasonably blame me; alleging that I am not a man of letters. Foolish folks! do they not know that I might retort as Marius did to the Roman Patricians by saying: That they, who deck themselves out in the labours of others will not allow me my own. They will say that I, having no literary skill, cannot properly express that which I desire to treat of, but they do not know that my subjects are to be dealt with by experience rather than by words; and experience has been the mistress of those who wrote well. And so, as mistress, I will cite her in all cases.

No human investigation can be called real knowledge if it does not pass through mathematical demonstrations; and if you say that the kinds of knowledge that begin and end in the mind have any value as truth, this cannot be conceded, but rather must be denied for many reasons, and first of all because in such mental discussions there is no experimentation, without which nothing provides certainty of itself.

I believe man will fly and I base this assumption on the fact that God has blessed us with minds that are capable of imagining it. Anything that can be dreamt of will eventually be built. Anyone who says otherwise is a fool.
(As quoted by a fictional Leonardo in DaVinci Demons)

Quando ouvimos os sinos, ouvimos aquilo que já trazemos em nós mesmos como modelo. Sou da opinião que não se deverá desprezar aquele que olhar atentamente para as manchas da parede, para os carvões sobre a grelha, para as nuvens, ou para a correnteza da água, descobrindo, assim, coisas maravilhosas. O génio do pintor há-de se apossar de todas essas coisas para criar composições diversas: luta de homens e de animais, paisagens, monstros, demónios e outras coisas fantásticas. Tudo, enfim, servirá para engrandecer o artista.