To praise it would amount to praising myself. For the entire content of the work … coincides almost exactly with my own meditations which have occupi… - Carl Friedrich Gauss

Letter to Bessel (1826), quoted in Dunnington, G. Waldo. "Gauss, His Disquisitiones Arithmeticae, and His Contemporaries in the Institut de France." National Mathematics Magazine 9.7 (1935): 187-192.

If the object of all human investigation were but to produce in cognition a reflection of the world as it exists, of what value would be all its labor and pains, which could result only in vain repetition, in an imitation within the soul of that which exists without it?

I mean the word proof not in the sense of the lawyers, who set two half proofs equal to a whole one, but in the sense of a mathematician, where ½ proof = 0, and it is demanded for proof that every doubt becomes impossible.