Full Idea
Notwithstanding my infinitesimal calculus, I do not admit any real infinite numbers, even though I confess that the multitude of things surpasses any finite number, or rather any number. ..I consider infinitesimal quantities to be useful fictions.
Clarification
[Leibniz was one of the inventors of calculus]
Gist of Idea
I don't admit infinite numbers, and consider infinitesimals to be useful fictions
Source
Gottfried Leibniz (Letters to Samuel Masson [1716], 1716)
Book Reference
Leibniz,Gottfried: 'Philosophical Essays', ed/tr. Arlew,R /Garber,D [Hackett 1989], p.229
A Reaction
With the phrase 'useful fictions' we seem to have jumped straight into Harty Field. I'm with Leibniz on this one. The history of mathematics is a series of ingenious inventions, whenever they seem to make further exciting proofs possible.