Introducing 28 varied pieces, Lopate, an essayist's essayist, eagerly claims that he feels no temptation to manicure his prose. ''It goes against the grain to take myself or the art of prose so seriously,'' he writes. ''Flaubert's le mot juste makes me want to giggle.'' Should we believe him? On the one hand, these essays -- remembrances of friends and lovers, reflections on teaching and urban life, and what's likely to be the best thing that will ever be written about Godard's ''Contempt'' -- look too solidly built to have been easy work. (There is no slack, so how could he be slacking?) On the other, they're consistently charged with a feeling of discovery -- a sense of learning on the run that suggests Lopate's been making it up (beautifully) as he's gone along.