Of Hucbald’s life little is known save that he was born about 840, that he was a monk, a poet, and a musician, a disciple of St. Remy of Auxerre and a friend of St. Odo of Cluny. Up to within recent years several important works on music were attributed to him, of which only one seems now to be actually his--the tract, _De Harmonica Institutione_, of which several copies are in existence. This and the _Musica Enchiriadis_ of his friend St. Odo are responsible for the widespread belief that polyphony actually sprang from a hideous progression of empty fourths and fifths. Both theorists, in their efforts to confine the current form of extemporized descant in the strict bounds of theory, reduced it thus: to a given melody taken from the plain-song of the church the descanter or organizer added another at the interval of a fifth or fourth below, which followed the first melody or _cantus firmus_ note by note in strictly parallel movement. The fourth seems to have been regarded as the pleasanter of the intervals, though, as we shall see, it led composers into difficulties, to overcome which Hucbald himself proposed a relaxation of the stiff parallel movement between the parts. In the strict organum or _diaphony_ the movement was thus:
Either or both of the parts might be doubled at the octave, in which case the diaphony was called composite.
Just why the intervals of the fifth and fourth should have been chosen for this parallel music, which is excruciating to our modern ears, is not positively known. The simple obvious answer to the riddle is that Hucbald and his contemporaries based their theories on the theories of the Greeks, who regarded the fifth and fourth as consonances nearest the perfect consonance of the octave and unison. But in that case we have to ask ourselves why Hucbald and his followers regarded the diaphony of the fourth as pleasanter than that of the fifth which they none the less acknowledged was more nearly perfect. Dr. Hugo Riemann has suggested a solution to this difficulty which is in substance that organum was an attempt to assimilate elements of an ancient art of singing practised by the Welsh and other Celtic singers. The Welsh scale is a _pentatonic_ scale, that is, a scale of five steps in which half steps are skipped. In terms of the keyboard, it can be represented by a scale starting upon E-flat and proceeding to the E-flat above or below only by way of the black keys between or by a similar progression between any other two black keys an octave apart. In such a scale parallel fourths are impossible, as indeed they are in the Greek scales of eight notes upon which the church music was based; but whereas the progression of the fourths in the Greek scales is broken by the imperfect and very unpleasant interval of the tritone, in the pentatonic scale it is interrupted by the pleasing major third. Such a progression of fourths and thirds seems to spring almost naturally from the pentatonic scales and was very likely much practised by the ancient Welsh singers.[65] A comparison of two examples will make the difference obvious.