  We present a new English translation of L.E.J. Brouwer's paper `De
onbetrouwbaarheid der logische principes' (The unreliability of the logical
principles) of 1908, together with a philosophical and historical introduction.
In this paper Brouwer for the first time objected to the idea that the
Principle of the Excluded Middle is valid. We discuss the circumstances under
which the manuscript was submitted and accepted, Brouwer's ideas on the
principle of the excluded middle, its consistency and partial validity, and his
argument against the possibility of absolutely undecidable propositions. We
note that principled objections to the general excluded middle similar to
Brouwer's had been advanced in print by Jules Molk two years before. Finally,
we discuss the influence on George Griss' negationless mathematics.
