I also have a sneaky, largely untested theory that small ensembles were made more acceptable by the rise of solo, duet and trio playing in the improv movement from the late-60s onwards.

Anyway, here are some duos that occur to me:

• Martial Solal with NHOP (Movability, mMPS); with Michel Portal (Fast Mood);

• Stan Tracey with Roy Babbington (‘Plays Duke Ellington’)

• Stan Tracey with son Clark Tracey (’Soundcheck’)

• Archie Shepp with Horace Parlan (‘Goin’ Home’ and ‘Trouble in Mind’), or Mal Waldron (‘Left Alone’), or Abdullah Ibrahim (actually called ‘Duet’, I think);

• Art Pepper with George Cables (Tete-a-Tete and Goin’ Home)

And, to reinforce my own argument about duets in free improv circles, here are some I’m familiar with — and they wouldn’t necessarily frighten the horses:

• Evan Parker and Stan Tracey (‘Crevulations’ and ‘Suspensions & Anticipations’);

• Evan Parker with John Tilbury (Two Chapters and an Epilogue — free music but gently meditative and reflective — real ‘listening improv’)

• Anthony Braxton and Giorgio Gaslini (‘Four Pieces’) and AB with Dave Holland and/or Richard Teitelbaum (Duet/Trio)

• Sam Rivers with Dave Holland (2 volumes)