With Michael Jackson and Michael Jordan, I know they're two entirely different guys. I just can't remember which name applies to which guy. (And if you feel moved to tell me, you're missing the point. I could look it up. I have looked it up, more than once. But then I always forget again.) The problem is probably that I'm not very interested in the work of either.
With Reese Witherspoon and Rene Zellweger, I didn't realize that they were two different people. I had an amalgam of them in my head, who had done all the work I knew of both, and whenever I saw a reference to either, I thought of the amalgam, not remembering that, on previous occasions, she had a different name. I only discovered this when I looked up one's Wikipedia entry and was puzzled at not seeing listed movies that the other one had made.
Even after that, I still have not, however, sorted out in my head which one is which. The same applies to Norman Mailer and Philip Roth. I know there's two guys, but I can't remember which one did what, nor can I bring myself to care enough to read it.
I also sometimes have trouble remembering which opera titles are by Giuseppe Verdi and which by Giacomo Puccini. I have no trouble telling the men apart, and I'm sure of the assignation of many of the operas; I just can't always be sure. This comes of not caring much about opera, and it's the only case of this trouble I have in classical music. Might I confuse the Symphony No. 5 of Sergei Prokofiev with that of Dmitri Shostakovich, for instance? Of course not; I know both almost by heart, and they're totally distinct.
I also have no trouble remembering, at least for after the early period, which Beatles songs are by John Lennon and which by Paul McCartney. Since they're all officially listed as collaborations, this is tricky for a lot of people, but not me. And, again, the reason is: I care about the work.
This post brought to you courtesy of a long, indulgent article about Norman Mailer in the New Yorker.