Title generally applied solely to Beethoven's pf. sonata No.29 in B♭ major, Op.106, comp. 1817–18, but in a letter written in Jan. 1817 Beethoven said he had decided to use the word ‘Hammerklavier’ (Ger., ‘pianoforte’) on all his pf. mus. with Ger. titles, adding ‘this is to be clearly understood once and for all’.