Hrm, I was about to say you should check www.allmusic.com, but I just looked at their definition of soul and it’s not so hot. (For one thing, the allmusic definition calls soul the result of the urbanization and commercialization of R&B during the 1960s, when R&B was already plenty urbanized and commercialized by the late 1940s.) So I’ll give a shot myself. (Takes a deep breath…)
Soul music is the result of the mixture of 1950s R&B and 1950s (black) gospel music. The two defining events in soul music history are Ray Charles’s 1955 “I Got a Woman,” based on a gospel song, and Sam Cooke’s 1956 departure from the gospel group the Soul Stirrers to pursue a pop music career.
This mixture of gospel and R&B was an instant hit, and by the early 60s soul had become the most popular form of R&B. By the early 60s, two dominant styles had emerged: northern soul and southern soul.
Northern soul was slick, pop oriented and often heavily produced (with strings, etc.) The “Motown sound” out of Detroit was quintessential northern soul: the Supremes, Smokey Robinson, Marvin Gaye, etc.
Southern soul was rawer, and stuck closer to soul’s blues and gospel roots. Stax Records in Memphis produced many of the classic southern soul records by Otis Redding, Sam and Dave, Booker T and MGs and others. (There’s a great bit in Peter Guralnick’s book Sweet Soul Music about the rivalry between northern soul and southern soul fans.)
The peak of soul was in the mid-60s. By the early 70s, soul had begun to fracture and transform–James Brown had turned soul into funk, while in Philadelphia the ultra-slick Philly Sound, exemplified by Barry White, made Motown’s records sound postively primitive. And then along came the disco phenomenon. By the end of the 70s, soul had petered out as a force in popular music.
Soul was hugely influential in its day–the style of a zillion rock performers during the 70s and 80s was permeated by it–and soul still pops up on the charts from time to time. Macy Gray’s 1999 hit “I Try” was a soul song, for example.
And many of the original performers are still at it, too. If you like soul music, you should run, not walk, to your nearest record store and buy Solomon Burke’s latest album, Don’t Give Up On Me. Burke was one of the great soul singers of the 60s (and he’s quite a character–read Guralnick’s book.) He’s in top form on this album, singing brand new songs by Tom Waits, Bob Dylan, Elvis Costello, and others.