Full Idea
The concern of mathematical intuitionists was that the use of certain forms of inference generates, not contradiction, but unjustified assertions.
Gist of Idea
Intuitonists in mathematics worried about unjustified assertion, as well as contradiction
Source
report of Luitzen E.J. Brouwer (Intuitionism and Formalism [1912]) by A.George / D.J.Velleman - Philosophies of Mathematics Ch.6
Book Reference
George,A/Velleman D.J.: 'Philosophies of Mathematics' [Blackwell 2002], p.156
A Reaction
This seems to be the real origin of the verificationist idea in the theory of meaning. It is a hugely revolutionary idea - that ideas are not only ruled out of court by contradiction, but that there are other criteria which should also be met.