In his book, English Pasts, reviewing a volume of Bertrand Russell's correspondence, Stefan Collini quotes from one of the letters:
'"I saw Moore in the evening, and discussed whether there was any difference between knowing Arithmetic and knowing one's grandmother; he thinks not."'
Words fail me. At one point I wanted to go to grad school in philosophy. Professors who thought Russell was the epitome of a philosopher put me off the idea. How to answer the question of whether or not the present King of France was bald - this was a burning philosophical problem chez Russell!
(Answer: both the statement that he is and that he isn't are false, in case you're wondering.)