-Philosophy is not a theory, - asserted Austro-British philosopher Ludwig Wittgenstein (1889-1951), -but an activity.- In this 1921 opus, his only philosophical work published during his lifetime, Wit.... -Philosophy is not a theory, - asserted Austro-British philosopher Ludwig Wittgenstein (1889-1951), -but an activity.- In this 1921 opus, his only philosophical work published during his lifetime, Wit...