> So that would point to Feynman's calculus book being "Calculus for the Practical Man" by J.E.Thompson rather than Silvanus P Thompson's "Calculus Made Easy", whose second edition came out in 1914. I would not be surprised that Feynman read and used both.
It's just that the quote on fools is very prominent in the beginning of Calculus Made Easy, and the author continues to hilariously refer to both other people and himself as fools. I searched inside Calculus for the Practical Man [1] on archive.org for the word "fool" without a single hit.
I'm sure Feynman read both, but I was interested in the origin of the quote, since I learned it a few days ago and think it's very inspirational. Feynman was constantly arguing that everyone has the capacity to figure things out, it's just that they rarely practice it.