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In Celtic Music: A Complete Guide, June Skinner Sawyers acknowledges six Celtic nationalities divided into two groups according to their linguistic heritage. The Q-Celtic nationalities are the Irish, Scottish and Manx peoples, while the P-Celtic groups are the Cornish, Bretons and Welsh peoples.
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The Breton musician Alan Stivell uses a similar dichotomy, between the Gaelic (Irish/Scottish/Manx) branch and the Brythonic (Breton/Welsh/Cornish) group, which differentiate "mostly by the extended range (sometimes more than two octaves) of Irish and Scottish melodies and the closed range of Breton and Welsh melodies (often reduced to a half-octave), and by the frequent use of the pure pentatonic scale in Gaelic music."
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The Breton musician Alan Stivell uses a similar dichotomy, between the Gaelic (Irish/Scottish/Manx) branch and the Brythonic (Breton/Welsh/Cornish) group, which differentiate "mostly by the extended range (sometimes more than two octaves) of Irish and Scottish melodies and the closed range of Breton and Welsh melodies (often reduced to a half-octave), and by the frequent use of the pure pentatonic scale in Gaelic music."