It is assumed that the word 'sankyoku' started to be used to distinguish these instruments and music genres from 'hei-kyoku' (music played on heike-biwa, or Japanese lute used as accompaniment for the recitation of Heike Monogatari), their area of expertise, which had been performed for a long time.
これらの楽器や音楽を、同じく彼らの専門音楽であり、はるかに以前から行なわれて来た「平曲」(平家琵琶の音楽)に対して区別するために「三曲」という言葉が使われ始めたのではないかと思われる。