Alert concertgoers will be aware that the orchestral clarinetist is often seen on stage with not one, but two clarinets, which appear to be nearly identical. These are clarinets in the keys of B-flat and A, and, in truth, they very nearly are the same—identical in keywork and playing approach. The difference is one of an inch or so in length, giving the A clarinet a range that is deeper by one semitone.
It seems a redundancy to have two instruments so close in range. The ubiquity of the B-flat and A clarinets is a vestige of the clarinet’s early days, when its simpler keywork made it poorly suited to playing in more than a handful of keys; early clarinetists owned several instruments of different transpositions so that they could play in whatever key was required. But the modern instrument has a more involved mechanism that allows much more chromatic agility. The problem that remains is that the clarinet has accumulated two hundred and fifty years of repertoire, some of which calls for the instrument in B-flat, some of which calls for the instrument in A, and even some that calls for a little of each.