Federer’s forehand is a great liquid whip, his backhand a one-hander that he can drive flat, load with topspin, or slice — the slice with such snap that the ball turns shapes in the air and skids on the grass to maybe ankle height. His serve has world-class pace and a degree of placement and variety no one else comes close to; the service motion is lithe and uneccentric, distinctive (on TV) only in a certain eel-like all-body snap at the moment of impact. His anticipation and court sense are otherworldly, and his footwork is the best in the game — as a child, he was also a soccer prodigy. All this is true, and yet none of it really explains anything or evokes the experience of watching this man play. Of witnessing, firsthand, the beauty and genius of his game. You more have to come at the aesthetic stuff obliquely, to talk around it, or — as Aquinas did with his own ineffable subject — to try to define it in terms of what it is not.