In Germany, where academic philosophers still equate dryness with seriousness, Peter Sloterdijk has a near-monopoly on irreverence. This is an important element of his wide appeal, as is his eagerness to offer an opinion on absolutely anything—from psychoanalysis to finance, Islam to Soviet modernism, the ozone layer to Neanderthal sexuality. An essay on anger can suddenly plunge into a history of smiling; a meditation on America may veer into a history of frivolity. His magnum opus, the “Spheres” trilogy, nearly three thousand pages long, includes a rhapsodic excursus on rituals of human-placenta disposal. He is almost farcically productive.