The temptation to divide the work of great composers into three periods has assailed many critics, Lenz having done it so plausibly with Beethoven's music. Lenz, of course, should have been a warning rather than a model, and would have been if his mere plausibility had been a little more obvious. As it was, his system commended itself in Beethoven's case because in a rough and ready way it worked well enough; and it has done so in the case of many a later composer, if only because it saved many a later critic a deal of trouble.