It is possible, of course, to operate with figures mechanically, just as it is possible to speak like a parrot: but that hardly deserves the names of thought. It only becomes possible at all after the mathematical notation has, as a result of genuine thought, been so developed that it does the thinking for us, so to speak.

The Foundations of Arithmetic: A Logico-Mathematical Enquiry Into the Concept of Number (ed. Northwestern University Press, 1980) - ISBN: 9780810106055