Francis B. Carpenter, Six Months at the White House

“ [314] the course of my law-reading, I constantly came upon the word demonstrate. I thought at first that I understood its meaning, but soon became satisfied that I did not. I said to myself, “What do I mean when I demonstrate more than when I reason or prove? How does demonstration differ from any other proof?” I consulted Webster's Dictionary. That told of “certain proof,” “proof beyond the possibility of doubt;” but I could form no idea what sort of proof that was. I thought a great many things were proved beyond a possibility of doubt, without recourse to any such extraordinary process of reasoning as I understood “demonstration” to be. I consulted all the dictionaries and books of reference I could find, but with no better results. You might as well have defined blue to a blind man. At last I said, “Lincoln, you can never make a lawyer if you do not understand what demonstrate means;” and I left my situation in Springfield, went home to my father's house, and stayed there till I could give any proposition in the six books of Euclid at sight. I then found out what “demonstrate” means, and went back to my law-studies.”

I could not refrain from saying, in my admiration at such a development of character and genius combined: “Mr. Lincoln, your success is no longer a marvel. It is the legitimate result of adequate causes. You deserve it all, and a great deal more. If you will permit me, I would like to use this fact ”