Diarmuid Breatnach
(Reading time text: 4 mins)
Replying to a query on Quora on the above question, I spent some time thinking and typing the reply and then thought I might as well make that effort available to a wider audience. I have participated in many Irish instrumental music and singing sessions over decades, mostly in London and Dublin and I have two brothers who are musicians and another who is a singer. I am myself a singer, not an instrument player, nor an academic but will attempt an answer. I would recommend consulting the Irish Traditional Music Archive and reading books on the subject such as Ó Súilleabháin’s and Ó Lochlainn.
Traditional Irish music has had many external influences and among the main forms of its dance expression, jigs, hornpipes and reels, only the latter is considered originally Irish. Polkas are particularly popular in Kerry and, I suppose, built around reels. There are also slip-jigs.
The best way to experience these is probably is probably at or viewing a set-dancing session. These are based in form on the “quadrilles” of the Napoleonic period (which can be found as far away as Latin America and Cuba) and are similar to English and US Old Timey square dancing. Probably all the variants of the Irish instrumental dance music will be heard performed among the various set-dances — virtually all sequentially in the deceptively-named “Plain Set”.
The form of dance called “sean-nós” (see description of the singing form by the same name further down) is individual expression, fast footwork with what one might also call “ornamentations”, similar to tap-dancing. The arms are held loosely down to the side or elbows to the side, slightly extended but also loosely. The overall posture may be erect or slightly stooped.
In terms of instruments used today, not one is believed to be originally Irish except the harp (which incidentally is the symbol of the Irish state, the only state in the world to feature a musical instrument in that capacity though we are far from being the only nation with a harp tradition).

The harp (there two main kinds, the smaller knee-standing and the larger resting on the floor between the knees) was described by Norman travellers (spies) prior to their invasion of Ireland but were known also in Wales (observers remarked not only on the aesthetic quality of the performances but also on their speed). A kind of drum was referred to by the travellers and some kind of flute but without any detail on either. The proliferation of instruments in a traditional Irish session are therefore far from being originally Irish: fiddle (violin), uilleann pipe, flute, whistle, accordion (piano or more likely button), concertina, melodeon, bazouki, mandolin, banjo and …. guitar. This last is mostly performed as an underlying rhythm instrument, a function also of the bodhrán (a kind of one-sided drum) and one may also hear a pair of spoons or sections of rib bones played for percussion. The guitar-player is often also the singer and given space to do so accompanied by his guitar, presumably in recompense for his restriction to rhythm performance the rest of the time. In many sessions there has grown sadly a tendency to restrict the performance of song to this individual or some other in the circle of musicians whereas in the past a member of the audience would perform the song; this restriction has led to the growth of song and even voice-only sessions (such as the Góilín in Dublin).
We owe the typical instruments in traditional Irish music to northern and central Europe, the Middle and Far East and to Africa. Many other instruments have been brought into use in performing Irish traditional music (including, famously, the Australian didgeridoo) but, apart from the proliferation of variations on the whistle, they have as yet failed to win popularity among musicians.
Traditional march airs also exist and, to my ear, have a tendency to be fast for the purpose. I have speculated that these represented trotting horses of the elites or warrior-caste with lower-ranking fighters running alongside — but that is pure speculation.
There are many slow airs and waltzes, definitely an import, have been composed and are also played.
TRADITIONAL, ETHNIC
With regard to the ethnicity of the performers this is not of great relevance and Irish traditional music on instruments and in voice is being played well in many different parts of the world or in Ireland by musicians with a non-Irish ethnic background. Naturally too the Irish diaspora has spawned many excellent traditional Irish musicians (and, we can remark in passing, in many other genres too: rock, pop, blues, jazz, classical).
The term “traditional” itself can open up a debate but with regard to song, I was offered this interesting definition some years ago: “author unknown, performed over three generations.” Authorship is therefore an issue as is permanency (or at least persistency). One feature of traditional music throughout the world, according to Ó Súilleabháin is never to end in a crescendo (although occasionally one may hear a traditional song or ballad treated in this way, it is rare).
However, as with “tunes” or “airs” in instrumental music, songs are being composed all along within the traditional or folk form, sometimes re-using known airs, sometimes adapting them and on occasion composing new ones.
It is important to note that ballads are not considered a “traditional” form, having entered Ireland in the 18th and 19th centuries but they are accepted in traditional singing circles.

THE SINGER AND THE SONG
Traditional-style singers not only eschew crescendos but also, in general, bodily gestures or dramatic pauses or changes of volume. There are emphases rendered on occasion but these tend to be subtle.
A form of singing known as “sean-nós” (literally ‘old style’) exists with regional variations. From experience and perception (but without formal study) I would say that the main distinguishing feature of this form is in the ornamentation of notes, viz. drawing some out to briefly twist around them (interestingly, one verb in Irish for “play” as in instrument or “sing” is “cas”, literally “twist/ turn/ weave”) and the ending of a line may have an additional note added. The Qawwali religious music of Pakistan and Indian shares many features as does parts of the Flamenco singing, albeit the latter is loudly expressive.
In terms of the great themes of Irish song (and at times of instrumental pieces) these are overwhelmingly love, patriotic struggle and emigration, with sub-categories, including some that merge two or even three of the main themes (hear for example “Skibereen” or the waltz-air “Slieve na mBan”.
PLEASE DON’T CLAP ….
A very important element of Irish traditional and folk singing is not only the performance but also the audience. The tradition is not for choral or duet etc singing with harmonies, though these exist but rather for the single voice. In this we differ from other Celtic nations such as the Welsh and Bretons but parallel the Scottish tradition as well as some other folk traditions, including some English and USA Old Timey expressions.
The tradition has been that a singer will be heard through to the end with perhaps some sounds of encouragement at various junctures (on occasion I have observed a noisy Irish pub become suddenly silent as the customers become aware that a song is being sung, remaining totally silent until the end of the song). Should there be a chorus, listeners may join in and a well-known and appreciated line may get listeners joining in too (think for example of the last line in the non-traditional form — but often sung in sean-nós style — ballad about the Great Hunger: “… revenge for Skibereen!”).
I should mention here that accompanying the beat in traditional music by clapping is certainly not “cool”, although traditional musicians performing on stage have been seen to encourage it (presumably in order to reduce the isolation feeling of the performers and to increase the enjoyment of non-perceptive listeners). In fact clapping overcomes the nuances of the performance as well as the concentration of the listener, therefore limiting the depth of the experience. “Tap feet by all means and clap at the end if you please” is the general rule.
I must note also in conclusion that Irish/ Scottish traditional music with some English folk contribution are the main influences in not only Old Timey USA music but also bluegrass and country & western, with spillover into some other forms. As such, this fount of music is responsible for the creation of the “white” or “European-origin” popular music of the USA, ie around half of the entire body. The other half is of African origin, in blues and jazz (in so far as these are not the same thing), giving rise to rock n’roll, swing etc. But both these “halves” have naturally had an influence on the other and in Ireland, traditional music is also influenced by — and contributes to — “crossover” variations of music.
I would comment also that socially and politically Irish musicians have tended to identify to one degree or another with the people and their resistance and were often persecuted for doing so. This was natural, given that they mostly came from the Irish population and that was where they found their audience. In that regard it is sad to note that some, including the Chieftains musician group and singer Imelda May, performed at a state banquet in Dublin a few years ago for the English Queen, who is head of the UK state and of the British Armed Forces, currently occupying one-sixth of our small national territory and also invading other parts of the world.
End.
USEFUL LINKS
Irish Traditional Music Archive: https://www.itma.ie/
Set-dancing: http://www.harpirishsetdancers.com/
Singing: https://www.facebook.com/AnGoilin/https://en.
Colm Ó Lochlainn: https://en.wikipedia.org/wiki/Colm_%C3%93_Lochlainn