The pianoforte trios of Haydn are perhaps the only-works of first-rate artistic importance in which there is no doubt that the earlier stages of the new art do not admit of sufficient polyphony to give the instruments fair play.
It would be impossible to add a note to Haydn's trio; the only question is how to account for the superfluity of much of the string parts and how to make the trios effective in performance.
Haydn finds the pianoforte so completely capable of expressing his meaning that he is at a loss to find independent material for any accompanying instruments; and the violoncello in his trios has, except perhaps in four passages in the whole collection of thirty-three works, not a note to play that is not already in the bass of the pianoforte; while the melodies of the violin are, more often than not, doubled in the treble.
In the time of Bach such writing was beautifully suited to enliven the dry glitter of the harpsichord, and Bach's duets for clavier and violin seem to have been sometimes played as trios with a violoncello playing from the clavier bass.
Classical and modern chamber-music in the sonata style consists mainly of string-quartets for 2 violins, viola and violoncello; string-trios (rare, because very difficult to write sonorously); pianoforte-trios (pianoforte, violin and violoncello); pianoforte-quartets (pianoforte with string-trio); pianoforte-quintets (pianoforte with string-quartet); string-quintets (with 2 violas, very rarely with 2 violoncellos), and (in two important cases by Brahms) stringsextets.
The compositions of Haydn include 104 symphonies, 16 overtures, 76 quartets, 68 trios, 54 sonatas, 31 concertos and a large number of divertimentos, cassations and other instrumental pieces; 24 operas and dramatic pieces, 16 Masses, a Stabat Mater, interludes for the " Seven Words," 3 oratorios, 2 Te Deums and many smaller pieces for the church, over 40 songs, over 50 canons and arrangements of Scottish and Welsh national melodies.
In 1843 he became a member of the musical club who called themselves "The Juvenals," and for their meetings were written the trios and duets, music and words, which Wennerberg began to publish in 1846.
In 1860 he published his collected trios, as The Three.
And in the Anguttara we find set out in order first of all the units, then all the pairs, then all the trios, and so on.