Mouth music or “port a beul” is a style of Gaelic folk singing in which the words literally take the place of musical instruments. It's not just that mouth music is acapella singing, but that the lyrics were carefully chosen more for their sound value than for the meaning of the words. As a result, the lyrics to port a beul songs are usually light hearted or humorous and sometimes even raunchy. I was told by one Gaelic scholar that he even knew of X-rated port a beul lyrics, but that most people were too embarrassed to share those with folklorists!

Mouth music was used for two purposes- to teach fiddle tunes and to provide music for dances. Gaelic musical culture did not traditionally use written notation, so port a beul songs could be used in place of sheet music. A fiddler who knew how to sing the mouth music for a particular song also knew how to play the fiddle tune. The songs carried more information than written notation was capable of carrying, because the combination of consonant and vowel sounds in the lyrics would be used as a guide to how to approach the song. That's why the old Cape Breton fiddlers used to say that if you couldn't speak Gaelic, you could never learn how to play the fiddle properly.

Not many people would take a statement like that literally today, but it is true that you can hear a distinct difference between the playing styles of Gaelic-speaking and non-Gaelic-speaking fiddlers. Here's a beautiful example of authentic Gaelic mouth music from Dolores Keane.