He hypothesized that there was some relationship between his inability to read music and his deficiencies at mathematics: he was not good at processing symbols.
By far the most irritating thing about Reasons and Persons is Parfit's aversion to algebraic symbols; many of the arguments would be infinitely clearer and shorter if he introduced x's and y's, or used heuristic numbers. (See Tyler Cowen on this re Parfit's new book.) I had put this down to convention, but idiosyncrasy is a more believable explanation. His obsessive circling around the same thoughts, his sheer repetitiveness, also turns out to be a character trait. ["Every time he'd say, 'Larry, isn't that boring, don't you want some of my curry?' I'd say, 'No, Derek, I don't like curry.'"] MacFarquhar cleverly splices in bits of dialogue between Parfit and his wife Janet Radcliffe Richards; I find that I agree with JRR's positions on most cases. (Though unlike her I would cheerily agree to align myself with "those gloomy Scandinavians" who believe life, even at its best, is only just worth living.)
Two other factoids that really illuminate R&P:
- "Theodora and Derek were brilliant students, like their mother. ... Joanna, like her father, was bad at everything. Her teeth stuck out. She was also much too tall... [Derek's father] had a narrow life. He took refuge in two hobbies -- tennis, which he didn't play well, and stamp collecting... Parfit emerged from his childhood with the understanding that he and his mother and Theo were lucky and would live full lives, while Norman and Joanna were unlucky and would never be happy." This fleshes out the endless nattering on about full lives and crimped lives in part 4 of R&P.
- [At All Souls] "he had become, he realized, what psychiatrists call institutionalized -- a person for whom living in an institution feels much more normal than living in a family." This, it seems to me, makes his views on selflessness etc. fairly easy to understand, and also his inability to engage persuasively with the Bernard Williams/JRR point of view.
Finally, there is one of these decompositions-of-personality:
he pictures his thinking self as a government minister sitting behind a large desk, who writes a question on a piece of paper and puts it in his out-tray. The minister then sits idly at his desk, twiddling his thumbs, while in some back room civil servants labor furiously, come up with the answer, and place it in his in-tray.
Cf. the street that is John Davidson's heart, the household that is T.S. Eliot.