Each year more books purporting to introduce readers to jazz (and more jazz record guides) hit the market. You haven’t heard about most of them, and for good reason—they tend to be either dumbed-down or redundant. I would’ve never expected the consistently erudite and illuminating Kevin Whitehead (a regular commentator on NPR’s Fresh Air and a onetime Reader contributor) to enter the jazz-guide arena, but he accepted an invitation to write one from Oxford University Press. Last week his book Why Jazz? arrived in stores.