A quotation by Benjamin Peirce
Mathematics is the science which draws necessary conclusions.
Memoir read before the National Academy of Sciences in Washington, 1870.
[after proving Euler's formula eπi = -1 in a lecture]
Gentlemen, that is surely true, it is absolutely paradoxical; we cannot understand it, and we don't know what it means. But we have proved it, and therefore we know it is the truth.
Quoted in E Kasner and J Newman Mathematics and the Imagination (New York 1940)