That sometimes clear ... and sometimes vague stuff ... which is ... mathematics.

Quoted in P Davis and R Hersh

The history of mathematics, lacking the guidance of philosophy, [is] blind, while the philosophy of mathematics, turning its back on the most intriguing phenomena in the history of mathematics, is empty.

*Proofs and refutations* (Cambridge, 1976).

Blind commitment to a theory is not an intellectual virtue: it is an intellectual crime.