L. E. J. Brouwer (trans. by Arnold Dresden) (1913). ”Intuitionism and Formalism”. Bull. Amer. Math. Soc. 20 (2): sid. 81–96. doi:10.1090/s0002-9904-1913-02440-6.
Gillies, D. A. “Brouwer’s Philosophy of Mathematics.” Erkenntnis (1975-), vol. 15, no. 1, Springer, 1980, pp. 105–26, http://www.jstor.org/stable/20010688.