I'm afraid I used the terms "a capella" and "unaccompanied" interchangeably. That's probably not correct, since the Harvard Dictonary of Music defines "a capella" as "choral music without instrumental accompaniment," and I was using the term to refer to solo singing. The dictonary goes on to say - "Historians of the 19th century held the idea that all 'early music' - i.e. music before 1600 - was 'a capella'. Such a statement is correct, however, only with respect to strictly liturgical music, such as masses and motets. Secular music, whether for a soloist or a choral group, was frequently accompanied or duplicated by instruments, particularly in the period 1300 - 1450."

S. in Seattle