The Alexander Principle has been oversimplified by some people into the need to sit up straight"" but Barlow, Alexander's son-in-law and ""spiritual heir,"" demonstrates its validity inasmuch as the human body is essentially ""stupid"" and poorly adapted to the demands of holding itself upright. Posture studies prove that even athletes need to be taught body grammar: NECK FREE, HEAD FORWARD AND OUT; BACK, LENGTHEN AND WIDEN. . . . Barlow's secondary mission is to rescue Alexander from his crackpot image, but he fails to clarify all those nebulous terms like ""end-gaining,"" ""body constructs,"" and ""sexual flow"" (not to mention the ""spines"" of the pelvis). The key concept is USE -- a principle one suspects would be worth learning, but a word that only acquires more mystical and oscillating overtones in each successive redefinition. This is an insider's roadmap to help devotees plumb the psychophysical mechanics and spiritual consequences of ""head retraction."" Others will have to accept Barlow's summary reminder that ""Fortunately there has always been a hard core of common sense at the back of it all.