Now it is clear that if you sing a note, and then drive your voice gradually upward, you will presently come to a note which has the same kind of sound at a higher pitchan " octave " higher, according to the customary term. It is also clear that you can fill this intervening space in a very large number of 5 different ways, either running up continuously through the smallest intervals that your ear can detect, or starting with a larger unit and maintaining that all through, or selecting more or less arbitrarily a succession of notes some of which are contiguous and others separated by gaps. Oddly enough it is the last, and apparently the most artificial, of these methods which has given us what we call our " diatonic " scales: the ordinary major or minor scales in which for three hundred years or more the bulk of our music has been written. The scale of C major, for instance, proceeds by two tones, then a semitone, then three tones, then a semitone, and each " length " of it is called an octave because the upper note is at the eighth remove from the lower. The ordinary chromatic scale proceeds entirely by semitones, of which (as a tone equals two semitones) it obviously contains twelve.
This system of diatonic and chromatic scales did not fall from heaven like the Palladium or come to us, like an axiomatic law, straight out of the nature of things: it is the result of long and gradual evolution. Many other varieties are in use among other nations, and the reason why we prefer our own is that as a matter of experience we have found it the best and most flexible vehicle for composition. As we shall see later it did not come into general use until the second half of the sixteenth century (there is, of course, no sharp dividing line), and before it was generally adopted our musicians filled their octave in a number of other ways. These were the Ecclesiastical modes.
Open the piano and play the scale of D major. You will require for it two " black " notes, F # and C #. Now play the same octave using white notes alone: you will receive an entirely different aesthetic impression. You have just played the Dorian mode, or Mode I, as the Ecclesiastical writers called it. Let us pursue this investigation further: start not on D, but on E, and play through the octave using white notes alonethat is another mode, the Phrygian, or Mode III. Continue the same process upward, F to F, G to G, and so on, confining yourself to the white notes, and you will follow a series of different modes of which only one (C to C) coincides with our major scale And not only that, but each mode differs in sound from the others. All major scales are the same, except for distinctions of pitch:the intervals of all come in the same places. No two modes have their intervals in the same places: each has its own special and distinctive distribution of notes. From this two consequences follow: first that a melody in the Dorian mode would have a different character from one in the Phrygian;
secondly, that it was impossible to "modulate " in our sense of the term from one mode to another; they were too disparate in quality.
The modes have Greek names because they were Greek in origin. Apparently the earliest Greek " scale " was a short length of four notes called a tetrachord. Two of these put together made an octave, which the Greeks called Diapason, or " running all through ": and the different ways in which they filled the octave were called modes, and were named after different races Dorian, Phrygian, Aeolian and the like. A list of the Ecclesiastical modes is given at the end of this chapter.
There is one more point to be considered before we leave this piece of technical analysis. Recall the tune of " Ein Feste Burg," or of " The Bluebells of Scotland "; you will notice that it fills the octave from key note to key note, touching both extremes in its course. Now recall the tune of Tallis's Canon (" Glory to Thee ") or of " Robin Adair." You will notice that although the tune still extends through an octave it cuts across the keynote which falls neither at the top nor at the bottom, but in the middle. Each of the Ecclesiastical modes was divided according to a similar distinction: they were called authentic if they lay between their proper finals and plagal if they cut across them. So far as we can apply the nomenclature to our modern scale we may say that " Ein Feste Burg" is an authentic melody, " Glory to Thee " a plagal.
We can now reconstruct the scene of the discovery which did more than anything else to change the whole face of musical art. For material there were the modes, or rather such of them as the Church musicians considered specially solemn and dignified. For texture there was the single melodic line with no thought of separate voices in combination: for accompaniment there was the organ, the keys of which, when it attained to the dignity of a keyboard, were " as large as a knife-grinder's treadle," and required the whole strength of the clenched hand. The choirs were of boys and men, probably with rather ill-trained voices, and it was through this fact principally that the change came about. For men's voices naturally fall into the two groups of tenor and bass, pitched about a fourth or a fifth apart: and it became apparent that if the chant were put down to suit the basses it would be too low for the tenors, and if put up for the tenors too high to suit the basses. For a long time this was endured as one of those evils against which it is hopeless to struggle: thenit may have been as early as the ninth centurysome inspired precentor suggested that tenor and bass should sing their chant each at his own pitch, so that the voices ran simultaneously in parallel lines. Sometimes this was varied by holding the bass to a single note (like the drone of a bagpipe) while the tenor expatiated over the melody: sometimes both expedients were tried in alternation, or the choir began with one and ended with the other. From this primitive device, which was known by the name of " organum " or " diaphony," sprang the whole scheme of interwoven voices which culminates in the minor Mass and the Choral Symphony.
It would overbalance the proportions of this volume if we traced in any detail the gradual extension of this principle in early Church music: how the mediant crept in between the dominant and the final, how the latter was transposed an octave higher and so produced an entirely new kind of harmony, how in course of time composers began to see that the voices need not run always parallel, but could hold independent parts, one rising as another fell, and so produce effects of varied yet coherent beauty. And at this point another stream entered the channel: the stream of contemporary folk-music.
One of the most charming writers of the twelfth century, Gerald Barry, Archdeacon of St. David's, has left among his other works a description of Ireland, a description of Wales, and an account of his travels to the north of England. In Ireland, he notes, the harp playing has attained a high degree of skill, but Scotland and Wales are coming near to rival it: through Yorkshire and Northumberland he finds the people singing in two parts " by natural gift without training," and his climax is reached when he tells us that when his own countrymen come together they sing " in as many parts as there are voices." We should not, of course, lay too much stress on this last assertion: if it means anything more than an improvised cacophony it must be exaggerated out of all knowledge: but the most probable inference from it is that, at any rate in Wales and northern England, the idea of part singing as a means of artistic expression had taken hold of the populace some time before 1200. And although the Church was not very willing to receive hints from the laity, yet we must remember that the Saints' day festivals with their songs and miracle plays brought the two sides into ever closer contact: so there is nothing extravagant in the supposition that even in these early days the folk-music exercised some influence on the methods of Church composition as it undoubtedly did later on its themes and melodies.