MASSED voices will always be a potent musical medium. But performances [of J. S. Bach's ‘choral’ works] by 16 or so singers have now become commonplace (and some of us use fewer), reminding us that Bach's music can speak equally powerfully in many ways. So, with choir size, is personal taste all there is to it?

At the heart of Bach's incomparable output of church music stands the choir. And, just as we rightly expect Abbado, Rattle et al. to know a thing or two about Mahler's orchestra, so ought we to be able to assume that our Bach experts know their Bach choir. Yet, for all the recent advances in Baroque instrumental practice, this central vocal medium has rarely received serious attention. Conventional thinking rests content with the idea that a small choir of 12 or 16 fits the historical facts adequately. Unfortunately, it doesn’t.

A century before Bach, composers such as Praetorius and Schütz knew two quite distinct types of vocal choir. The capella sang mostly chorales and straightforward types of motet and, like our ‘chamber’ choirs, might vary in size but would generally have several voices per part. The other type might not look like a choir at all to us, yet this Favoritchor – a select group of solo voices – was the ‘favoured’ medium of the new Italianate concerted music, and the music it sang was technically much more demanding. When in large-scale concerted works these two types of choir appeared side by side, it was always the ‘solo’ choir (a one-to-a-part ‘consort’, as we might call it) that was the main protagonist; the larger choir generally functioned as a wholly subsidiary ripieno group, ‘filling out’ the texture from time to time.

Bach, together with most of his contemporaries, was a direct heir to these 17th-century traditions. Of course much had changed, but the underlying principles remained constant; elaborate concerted music was essentially for soloists, simpler and more conservative idioms were choral (in the modern sense). At Leipzig, where Bach spent the last 27 years of his life, the larger groups sang the old motets on an almost daily basis but played little or no part in concerted music-making. (Clearly, by Mendelssohn's day, another 100 years on, things had changed substantially.)