 The Dutch mathematician L. E. J. Brouwer (1881–1966) is best known as the founder of the philosophy of (neo)intuitionism (Brouwer [1975]; van Dalen 1998). Brouwer’s highly idealist views on mathematics bore some resemblance to Kant’s. For Brouwer, mathematical concepts are admissible only if they are adequately grounded in intuition, mathematical theories are significant only if they concern entities which are constructed out of something given immediately in intuition, and mathematical demonstration is a form of construction in intuition. While admitting that the emergence of noneuclidean geometry had discredited Kant’s view of space, Brouwer held, in opposition to the logicists (whom he called “formalists”) that arithmetic, and so all mathematics, must derive from temporal intuition.