Here's the scenario: composer x writes a work for solo instrument + orchestra that is naturally enough called a Concerto. The composer then produces a piano reduction of the orchestral material of the Concerto and calls this new version of the work a "Sonata".
What do you think of this idea?
I can think of a specific example of a composer doing this.
I understand the logic behind doing this; it's easier to get perfomances when only two players are required, however I'd have trouble myself going as far as calling a concerto a "sonata" just because the instrumentation was different.