Finding a live tradition of polyphonic singing in Iceland was one of the highlights of the study of European polyphony – both professional and folk. A live tradition of polyphony in Iceland was particularly important for musicologists studying medieval European polyphony, because of its clear connections to the earliest types of organum [Organum was the first type of European professional polyphony, that appeared at the end of the 9th – beginning of the 10th centuries]. Angel Hammerich published a pioneering article about the Icelandic two-part singing tradition twisongur, then Biarni Forstain published 42 examples of twisongur, and finally John Laif recorded on phonograph the examples of twisongur. Phonograph recordings proved the correctness of the transcriptions made by Forstain. The term twisongur literally means “two-singing”, and it is a traditional technique of the two-part performance of secular and sacred melodies. Hornbostel’s description of twisongur as “fifths organum with crossing parts” is quite accurate. Most of the time the parts move in parallel fifths in twisongur style, and at certain moment the parts shift places (the top part goes lower and the low part goes higher that the top part). Therefore the second part usually finishes with the note that the first part started at the beginning of the song. The leading genre of Icelandic traditional music, Rimur (epic songs), was also performed in twisongur style. Here are two typical examples of the earlier type of twisongur:
The tempo was usually very slow, and the sound of “empty” parallel fifths is very specific. Interestingly, in late medieval Europe parallel fifths were considered the biggest compositional mistake that a composer could make in composing polyphonic music. By the way, parallel fifths were considered a very serious mistake not only by Medieval European music theorists. I remember myself doing very much feared harmony tests at Tbilisi State Conservatory in the mid 1970s, and parallel fifths were still the most feared mistake for the students.

 Anther feature of the twisongur style is a very specific scale with a range of more than an octave:
The appearance of F and then F# an octave higher is particularly interesting. From the point of view of European scale systems the note F# cannot be a part of the scale. It just does not make any sense. The eighth step of the scale (F#) must be the “octave repetition” of the first step of the scale – F (“tonic”). And the tonic is the most important and stable step of the scale. Therefore, within the basic rules of the European classical musical system the Icelandic scale F, G, A, B, C, D, E, F#, G makes as much sense as a three-eyed human face. But of course, this is simply because the Icelandic scale is not based on the octave (eight note) scale system. The presence of the augmented octave points to the scales of the fifths diatonic system in Icelandic polyphonic singing (you may remember this scale from our discussion of the scales of Georgian traditional polyphonic music). This scale is created by two five-note rings, tied together (F, G, A, B, C, tied to C, D, E, F#, G. See Gogotishvili, 1982, 2004). The most important feature of this type of scale is that the fifths must be always perfect. Perfect fifths always cause the appearance of augmented fourths and augmented octaves (this is unavoidable). This is exactly what happens in the Icelandic twisongur. Another very interesting feature of the Icelandic twisongur is the wide use of the Lydian scale. In its “classical” understanding the Lydian scale is a string of white keys on the piano from F to the next F. This scale was never used by the greatest European classical composers (until the romantic style composers of the 19th century, like Chopin). The augmented fourth step of the Lydian scale (B) was particularly avoided as it was considered to be the “ugliest interval”. In some cultures (for example, in many Middle-Eastern cultures) this interval is traditionally considered the harshest and is very much avoided. In medieval European professional music this interval was also very much avoided, and was given a special name “Triton” (“three” “tones”, as it consists of three full tones, instead of the “normal” two full tones and a half tone to make a perfect fourth).
So, the Lydian scale for the European musical system, although it is the “ugliest” scale, is still an octave scale with “proper” seven notes (F, G, A, B, C, D, E, and at the end, of course, again F). But in the system of the fifths diatonic scales, it is the perfect fifth that rules, not the perfect octave, so this troubling high fourth step of the Lydian scale (B) causes the appearance of the incredible F# in the twisongur scale. This is a fifth diatonic scale on a Lydian basis.
There could be more than two singers and two parts in twisongur as well: “More elaborate versions of twisongur, with doublings at the octave for other vocal parts, and a great variety of freer forms, were performed in sacred and secular settings” (Hopkins, 2000:403). In later forms of twisongur parallel fifths could be sometimes replaced by unisons. Gregorian Chants and psalms could be performed in twisongur style as well.
We know that the Church was not happy with the appearance of polyphonic singing in the churches in the first place. There is a well-known written record in the Iceland “Episcopal Sagas” that Episcope Laurentius from Holar tried to ban polyphonic singing in the church in the 1320s . As we can see, there was something totally unacceptable in Icelandic polyphonic singing for the Medieval European musical system.