One of the schools of thought in the philosophy of mathematics, putting forth the theory that mathematics is an extension of logic and therefore all mathematics is reducible to logic.9 Bertrand Russell and Alfred North Whitehead championed this theory fathered by Gottlob Frege. Frege gave up on the project after Russell recognised a paradox exposing an inconsistency in naive set theory. Russell and Whitehead continued on with the project in their Principia Mathematica.