Sean, Ira -
I transcribed Lester Young's solo. Technically speaking, it is very simple to play -- even I can play it! But to conceive of it, to make it up on the spot, at that moment for that song and with the way Lady Day was singing and phrasing it, all while following that burly solo by the always excellent Ben Webster, and all in Pres' poignant and tender tone and timbre -- well, that's one in a million. (He was one of Benny Goodman's favourite musicians; hearing Pres playing a battered old metal clarinet once, but playing with such melodic inventiveness and lyrical charm, Goodman gave his own clarinet to Lester right on the spot.) That's why Billie Holiday nicknamed him Pres, for president of the saxophone, while he gave her the name Lady Day. I think she tried to sing like he played, and he tried to play like she sang. To your point about bringing our own ideals / sense of absolute (rather than relative) greatness to the table: I have to admit - I'd think that I'd call that a perfect performance even if I'd never heard another one before. And I think there were/are architects whose genius sometimes manifested not in the complexity of their ideas but in how they found a feature or golf hole or routing that fit the moment-land perfectly. And I suppose I'd like to believe that, if I can across an example of that kind of perfect moment, I could recognize and appreciate and 'evaluate' it despite the fact that I've seen so few great courses.