JAMES TAYLOR thinks the blues is just a bad dream, and Duke Ellington once wrote that the blues is a gray, gray day. But the blues is more; played and sung right, it can really heal the sick, raise the dead, make the lame walk and make the blind see. Because the blues is often spiritually cleansing. B.B. King brought his blues, the cleansing, uplifting type, to the still night air of Boston Common last week, and to a predominantly white audience, proving that even as far away from his turf as he was that Wednesday night, the blues reaches an awful lot of people.

But first the bad news: Paul Butterfield's new band. Butter used to have the best big band in rock music, and at times, it was clear that what he was actually fronting was a very good soul band, nearly of the caliber of the Motown house band. But in the last six or eight months, he has disbanded it, in favor of the six man band he originally started in 1965. (I found his horn section, nearly intact, backing Stevie Wonder at the Rolling Stones Concerts.) In 1965, Paul Butterfield formed the first, and maybe the best, integrated Chicago-style blues band. He had Mike Bloomfield and Elvin Bishop on guitars, Sam Lay on drums, Jerome Arnold on bass, and Mark Naftalin on keyboards. Magnificent blues musicians all, but the instantly recongizable names are Bloomfield and Bishop. The albums they made for Electra, particularly the first, rank with the finest blues albums to come from Chicago.

The new band, unfortunately, doesn't have Bloomfield or Bishop, and that's the origin of its many problems. Butterfield has essentially teamed with an old folkie named Geoff Muldaur and they are sharing the band. My first impulse on hearing Muldaur sing was that he was in the band because he had bought all the equipment, or because he had something on Butterfield. Whatever Muldaur can do, he cannot sing blues. He sings with a false casualness that does not disguise the weakness of his voice, which begins to sound like a pubescent thirteen year old's. He is devoid of stage presence, which, rather than making him seem casual, acts to underscore the weakness in his voice. Butterfield should share the vocal load with no one: there's no need, because he has the range, the experience, and the phrasing to carry a varied set of songs--though he's mainly singing blues.

The music itself was mediocre to ordinary; ordinary from the rhythm section and mediocre from the guitars. Lead guitarist Amos Garrett cannot hold a phrase on his instrument, which essentially means that he can't play a decent fill between phrases of the vocal, the most fundamental aspect of playing blues guitar. Its overall listen ability was a combination of general enjoyment and the knowledge that there's really not much you can do to the 12 bar blues format. "Walking Blues" opened the set and set its Chicago blues tone. Muldaur's songs, mercifully, were all together, so they were out of the way quickly. His slow blues featured a lot of slurring of words, another major blues vocal tradition but mishandled by him so that it became merely irritating. (If you want to hear what slurring can do, in terms of veiled threats, innuendo, and the like, listen to Jimmy Reed sing "Take Out Some Insurance.")

And yet the set was not a total loss. Butterfield took the last four songs, and made them a separate body from the rest of the show. With "Losin' Hand," he finally got the band into a groove they could manage, and then raced them through "CC Rider," "Mystery Train," and an encore of "You've Got All the Money," that was nearly worth the whole set. His harp work was stunning, and very much the focal point over the band's easy chording. Butterfield learned to play harp from the Chicago masters, Sonny Boy Williamson, Little Walter, and James Cotton especially. He's mastered their techniques, and added his own ideas and his strong sense of taste, that is, what sounds right. He plays only slightly derivative blues harp, and his fine blues singing matches it. Paul Butterfield has one of the best blues voices in the business. Again, it is more a question of learning than original gift, but he combines that learning with his own unique sense of taste.

BONNIE RAITT '70 had opened the show at 5 p.m., with her brand of tough chick blues. Bonnie plays fine guitar, and slide guitar, and would've been better off had she opened completely alone, instead of with her bassist. As it was she managed to give open support to a lot of her musical friends, who she introduced one by one through her set. Bonnie's music is summed up by a Sippie Wallace tune called "You Can Make Me Do Whatcha Wanna Do, But Ya Gotta Know How." It was her best effort for a crowd that was either still entering, or just beginning to get comfortable and in any case, certainly wasn't listening to her. John Payne's soprano took the song right back to the thirties and Bonnie Smith, where it belongs.

Bonnie Raito's is better suited for clubs than the open air. She suffered immeasurably with the sound system, neither she or her acoustic guitars could be fully heard, and I know I missed a lot of funny patter from up front. She calls it cruisin music, but it's really all blues.

Just as twilight began to fall into night, and while we were occupied with the sunset behind us. Sonny Freeman and the Unusuals opened B.B. King's set. Fittingly, B.B. came on just as night started to fall, for you can't listen to blues before nightfall, because it is a nighttime music. He dipped deep for his classics, as if he had to make sure of his audience. He opened with "Everyday I Have the Blues," and took us way down for "How Blue Can You Get." B.B. King plays guitar at ascending levels of intensity: he builds to a climax chorus always played with the horns.

The piano playing was excellent, particularly the honky tonk chording on "How Blue Can You Get." The song was made by B.B.'s strutting on the famous bridge. "Bought you a brand new Ford, you wanted a Cadillac. Bought you a ten dollar dinner, (swivel the hips, here) you said. "Thanks for the snack."

(When B.B. King sings blues, I believe, for an instant at least, that all the women in the world are evil. And, for that instant, I am vindicated.)

Once he had the audience, he moved on to the newer, more commercial music. He played a new song, "Ghetto Woman," and the now-famous "The Thrill is Gone." The sound from the band was the classic soul sound, particularly through the horns. He moved into a lower profile blues for "Someone Really Loves You," which ended on a magnificent final note, broken falsetto.

His guitar work was superlative. His lines slashed through the still night air, and, for the first time. I heard him use both speed and feedback, with taste and control.

Paul Butterfield came back for the encore, an instrumental, and the whole evening jelled into something consistent. He and B.B. played fills, solos, chords, traded licks.

As for defining that vaguest of popular music forms: I point to a B.B. King and say, "That's blues. "You gotta hear it and see it, and it's not that complicated. John Lee Hooker said it: The blues is simply the truth