During a rehearsal of Johann Sebastian Bach’s Cantata BWV 51 in Oxford in 2008, a colleague, whom I had invited to listen and to observe, advised quite simply: more shapes. The aim, I believe, was to lift the notes further from the page to create a more nuanced and stylish performance. This suited both the contrapuntal edifice of Bach’s music and the period instruments that we were using. On this occasion I was leading the ensemble and therefore in possession of greater authority than usual. I have nonetheless had similar subsequent experiences of this piece, and of similar repertoire, where I have possessed artistic licence to create a microcosm of musical shapes not found in the notated score. Indeed, I have found that such practice continues to be strongly encouraged within this genre....