Preliminary studies for the 'Philosophical investigations' : generally known as the Blue and Brown books / Blue and Brown books Blue and Brown books. Wittgenstein, Ludwig, 1889-1951. Wittgenstein, Ludwig, 1889-1951. Philosophische Untersuchungen. B3376.W563 P6 1969 107 WIB Oxford : Blackwell, 1969. 1969. 1969 Text xv, 192 p. : eng engger