"Metrical exactitude ... is the embodiment of slavishness in music, i.e., the music is the slave of the beat when it should be its master, exactly the opposite of what C.P.E. Bach suggested, in his Essay on the "True Art of Playing Keyboard Instruments," when he wrote that one should "endeavor to avoid everything mechanical and slavish. Play from the soul, not like a trained bird." Like the beating of the heart, the musical pulse needs to fluctuate in speed as the emotional content of the music fluctuates. Like the natural shifting accents in speech, musical accents need to shift according to the meaning being expressed. To feel perfect, music must be metrically imperfect."