Eight months after Karma, Leon Thomas had a contract with Bob Thiele's new label and two days in a New York studio, 21 and 22 October 1969. Spirits Known And Unknown, subtitled New Vocal Frontiers, is the record that came out of it, Flying Dutchman's first from a jazz perspective according to UK Vibe, and the first of four Thomas made for the label.

The band is the Sanders circle: Lonnie Liston Smith on piano, James Spaulding on alto and flute, Cecil McBee and Richard Davis on bass, Roy Haynes on drums, Richard Landrum on bongos, and Pharoah Sanders himself on tenor, credited as Little Rock, on Malcolm's Gone. Smith has said the three of them were pushing each other down experimental roads.

It opens with a shorter, more lyrical The Creator Has a Master Plan, the yodel bubbling up only in the refrains, which Thom Jurek at AllMusic calls one of the most criminally ignored tracks in Thomas's career. Echoes is the wordless piece Jazzwise picks as the peak of his horn-like vocal technique. Song for My Father is the Silver tune with Thomas's lyric, Damn Nam (Ain't Goin' to Vietnam) the topical one, and Let the Rain Fall on Me closes with a Smith piano solo. Christgau, giving it a B+, wrote that the subtitle was accurate: Thomas was the only interesting jazz singer to appear in a very long time. He even yodels.

Japanese CD edition from Solid's Flying Dutchman series.