"Since this art surpasses all human subtelty and the perspecuity of mortal talent and is truly a celestial gift and a very clear test of the capacity of man's minds, whoever applies himself to it will believe that there is nothing that he cannot understand."

“My personal affairs are not as highly esteemed as men commonly value their own interests—vain, empty affairs like those great clouds seen in the wake of the sunset which are meaningless and soon pass away.”

“I have accustomed my features always to assume an expression quite contrary to my feelings; thus I am able to feign outwardly, yet within know nothing of dissumulation. This habit is easy if compared to the practice of hoping for nothing, which I have bent my efforts toward acquiring for fifteen successive years, and have at last succeeded.”

“Although a long series of rules might be added and a long discourse given about them, we conclude our detailed consideration with the cubic, others being merely mentioned, even if generally, in passing. For as positio refers to a line, quadratum to the surface, and cubum to a solid body, it would be very foolish for us to go beyond this point. Nature does no permit it.”

“I am cold of heart, warm of brain, and given to never-ending meditation; I ponder over ideas, many and weighty, and even over things which can never come to pass.”

“This I recognize as unique and outstanding among my faults—the habit...of preferring to say above all things what I know to be displeasing to the ears of my hearers. ...I keep it up wilfully, in no way ignorant of how many enemies it makes for me. ...Yet I avoid this practice in the presence of my benefactors and of my superiors. It is enough not to fawn upon these, or at least not to flatter them.”

“I am able to admit two distinct trains of thought to my mind at the same time.”