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

And believe me, if I were again beginning my studies, I should follow the advice of Plato and start with the mathematical sciences, which proceed very cautiously and admit nothing as established until it has been rigorously demonstrated.

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.

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

See now the power of truth; the same experiment which at first glance seemed to show one thing, when more carefully examined, assures us of the contrary.

I do not know what to say in a case so surprising, so unlooked for and so novel.

I abjure with a sincere heart and unfeigned faith, I curse and detest the said errors and heresies, and generally all and every error and sect contrary to the Holy Catholic Church.