 The life of Brouwer was laden with conflicts, the most famous one being the conflict with David Hilbert, which eventually led to Brouwer’s expulsion from the board of the Mathematische Annalen. This conflict was part of the Grundlagenstreit that shook the mathematical society at the beginning of the 20th century and that emerged as a result of the appearance of paradoxes and highly nonconstructive proofs in mathematics. Philosophers and mathematicians were forced to acknowledge the lack of an epistemological and ontological basis for mathematics. Brouwer’s intuitionism is a philosophy of mathematics that aims to provide such a foundation.