American songwriter Peter Karp and Canadian-born blueswoman Sue Foley struck up a correspondence–by letter, which is news in itself. “As time went on,” their website says, “the letters they shared became more poignant, more revealing. Those letters became their songs.” Many if not most songs of whatever genre or nation get started in connection with romantic relationships, but this is something else again, and something new–somewhere between a collection of love songs and a documentary, for it has a ripped-from-real-life quality.

The joint album and tour that has resulted is called He Said, She Said and it includes songs sung by and written by both artists, although none they composed together. Most of them do seem to grow from a germ taken from a letter: “I’m scared, so very scared; for so long, seems like forever, I’ve wished for you,” or “It’s now 4 a.m.; the air outside is stagnant and this darkness is uncommonly warm.” The relationship grows volatile, passionate, troubled, affectionate. Any of these emotions could have been a basis for a conventional love song, but the songs on He Said, She Said are compelling precisely because they’re left a bit unfinished.

It’s a difficult songwriting problem, and part of the solution Karp and Foley find is to challenge themselves and each other in terms of exploring new styles. This isn’t a blues album, or an Americana singer-songwriter album, although it contains elements of both. The new mixture is especially noticeable in Foley’s songs, for these days blues is usually a music that stays in its own box. Her “Danger Lurks” is sort of a flamenco torch song, and listening to it you get the feeling that she delved into new musical territory as a way of understanding what was happening to her.

He Said, She Said is an experiment, and beyond that, it feels alive. Sue Foley and Peter Karp come to the Ark on Monday, May 17.