 But there are also substantial differences between the intuitionist and the formalist. For one thing, not only Brouwer but also many later constructivists refuse to identify provability with provability in some formal system. For another, formalists have generally felt free to help themselves to classical logic, and have emphasised the free creativity of the mathematician: she should be free to generate whatever mathematical theories she wishes, subject only to withdrawing them if they turn out to be inconsistent (in the chosen background logic). 