Soul music emerged in the late 1950s and early 1960s as one of the most distinctive forms in the history of American popular music. For black Americans especially, soul music defined the 1960s, offering a cultural soundtrack to the civil rights movement and the larger awakening of black consciousness and pride. Soul hits dominated the charts during that decade, but defining exactly what soul was proved no easy task, even for some of its greatest artists. Wilson Pickett defined soul as "nothin' but a feelin'." Don Covay said, "For a singer, soul is total vocal freedom." Aretha Franklin explained, "Soul to me is a feeling, a lot of depth and being able to bring to the surface that which is happening inside.… It's just the emotion, the way it affects other people." Elements of the genre live on, but the classic period of soul music, from...