** 1/2 MICHAEL ROTH: “Their Thought and Back Again.” (self-produced)

Michael Roth’s 40-minute opera “Their Thought and Back Again” is a little like an isometric exercise--music and text pushing against each other and neither getting anywhere. Given his background as house composer at the Old Globe Theater, it’s not surprising that Roth can write catchy, hip and suave tunes. The opera, originally combined with a dance work, is a series of six such songs in blues, rock, ragtime or pop opera style. They’re linked by short, pure-music sections that still wouldn’t be out of place in a Stephen Sondheim musical.

But such song styles set up certain expectations: some example of verbal wit, revelation of character or advancement of plot. All you get here, however, are text bits such as “Seeking a woman to bird dream car.” It doesn’t take long for that kind of thing to outstay its welcome even though the composer, musicians and the two vocal soloists do create particular moods or occasionally inflect individual words suggestively.

Celesta Tavera brings a coolish, classical soprano to her duties. Roxane Carrasco sings hers in a nasal pop style.

The two don’t blend well, but presumably this contrast is exactly what the composer wanted. The capable musicians, the Elan Ensemble String Quartet--violinists Hernan Constantino and Edmund Stein, violist John Stubbs and cellist Mary Oda Szanto--include Roth at the piano.

*

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