As the music is created by a sizable number of musicians working today, jazz is something other than—and maybe something more than—a heritage. It is a way to confront the particulars of the present day and give voice to what it feels like (and sounds like) to live in a time of seemingly endless access and cultural volatility. While some jazz critics are at home in the present (I’d like to think of myself as one of them), no writer has confronted the of-this-moment character of contemporary jazz with the clarity and authority that Nate Chinen has brought to it, first in his journalism and now in a daring and illuminating book, Playing Changes.