Intuitionism: Brouwer and Constructive Mathematics

L.E.J. Brouwer founded mathematical intuitionism in his 1907 doctoral dissertation at the University of Amsterdam, Over de Grondslagen der Wiskunde ("On the Foundations of Mathematics"), arguing that mathematics is fundamentally a mental activity — a free creation of the human mind grounded in a primordial intuition of time, the bare awareness of "two-oneness" or succession — rather than a body of mind-independent, platonic truths, or a formal game played with meaningless marks.