But after a while it occurred to some one to let a second set of voices sing the same chant at an interval of a fifth above the first.[10] This scheme, which, simple as it was, contained the seeds of wonderful developments, was probably first recommended by several practical advantages. When the chant was sung by two choirs, one made up of the high voices (soprano and tenors) and the other of the low voices (contraltos and basses) the interval of the octave was practically inconvenient because the low voices could not use their highest tones without throwing the high voices out of range, and the high voices could not use their lowest tones without similarly embarrassing the low ones. When the interval of the fifth was used, on the contrary, practically all the tones in both ranges, which are by nature about a fifth apart,[11] became available. This was a very practical argument in favor of chanting “at the fifth.” An even stronger one was the fact that, while fifths, like octaves, are harmonious and pleasant to the ear, without harshness or discordance, they are richer than octaves, and their constituents stand out distinct instead of merging into one impression, as do tones an octave apart; so that the practice of Organum, or chanting at the fifth, was harmonically sweet and full as well as melodically interesting. Organum came therefore into general and wide use in the mediæval church. Hucbald, a monkish writer of the tenth century, gives the following example of a fragment of plain chant “organized,” or sung by two voices a fifth apart:
FIGURE II. EXAMPLE OF ORGANUM.
In patris sempiturnus es filius.
The practice of Organum, crude as it may seem to modern ears, was or immense historical importance, as the first embodiment of that principle of combining various parts simultaneously which in due time produced all the resources of polyphony and of harmony. It is not necessary to examine here, in detail, all the stages of that long and weary journey which the mediæval composers made from this starting-point of Organum to the highly developed contrapuntal music of the sixteenth century. In all its aspects it was essentially a growth in definiteness, coherence, and heterogeneity. The parts were combined with more and more freedom, both as to their comparative rate of movement and as to the purity of the chords they made at prominent points (less harmonious intervals being gradually tolerated); the number of parts was increased, in spite of the great difficulties that each additional part must have meant to writers with inadequate experience and models; experiments were tried in combining together tunes already composed, popular songs and the like, trimming and twisting and compressing or expanding them to make them fit; the device of imitation, of which more will be said presently, was introduced in the interests of sense and coherence;[12] one experiment after another was tried, one resource after another was utilized, until eventually, in the sixteenth century, the art of ecclesiastical counterpoint[13] was fully established.
To this sixteenth-century music it is difficult for modern ears to listen appreciatively. The exact value and significance of chords, cadences, and melodic phrases, like the exact significance of words in language, depends so largely upon current usage and the mental habits it reposes upon, that it is as much an effort for modern listeners to comprehend mediæval music as it is for the modern reader to understand the vocabulary of Chaucer or Shakespeare. Just as words, in the course of long service, gradually take on new associations, new shades of suggestion, and even, in extreme cases, a significance quite opposite to their original one, so the material of music, as used to-day, has hundreds of associations and subtle shades of value, developed only during the last three hundred years, but nevertheless permeating our minds so thoroughly that it is almost impossible for us to think them away.
—Perhaps the most inveterate of these modern habits of musical thought is the harmonic habit. It is second nature for us to conduct all our musical thinking in terms of harmonic relations. We think of chords as related to one another in certain fixed ways, as forming groups or clusters just as definite as the groups of atoms in a chemical molecule. It is not more sure, for example, that in a molecule of water two atoms of hydrogen are engaged or held in combination by one atom of oxygen, than it is that in any key the dominant and sub-dominant chords are held in the position of subordinate companions by the tonic chord, and that the other chords of the key are held in more remote but still perfectly fixed relations with this Paterfamilias of the harmonic family. We think of the chords in a phrase, of whatever length and complexity, as progressing in a coherent series, as intertwined one with another by manifold relationships, and as embodying, all together, some one key. For us, every composition is in some particular key as inevitably as every poem or essay is in some particular language. We modulate freely, to be sure, from key to key; but this rather intensifies than obliterates our sense of key, just as the process of translating from one language to another intensifies our sense of the peculiar idioms of each. Our whole manner of thought would be as indescribably shocked by a passage which placed together, cheek by jowl, chords belonging to different keys, as by a sentence every word of which was drawn from a different tongue.
Now this habit of thought simply did not exist in Palestrina and his contemporaries and forerunners; it had not been evolved. The bit of Organum given in Figure II is hideous to modern ears just because it violates at every step our harmonic sense; it was pleasant to its composer, whoever he was, because he had no harmonic sense to be violated. To us, the sound of a tone with its fifth suggests immediately and inexorably the whole “triad” founded on that tone—root, third, fifth, and octave—and the key we consider it to be in. The sound of the tone and its fifth summons up in our imagination the whole chord and its key just as automatically as the sight of a horse’s head arouses in us an image of the trunk, legs, and tail that accompany it. This being the case, the bit of Organum quoted means for us a series of abrupt transitions from key to key, without warning, reason, or coherence. It is musical nonsense, gibberish, delirium. To its composer, on the contrary, it was merely an agreeable combination of two pleasing melodies in a harmonious interval. The chords used had for him no implications, no necessary relations, the observance of which made sense, the violation nonsense. They were pleasant combinations of sounds formed by the melodies in their progress; and that was all. Even more striking becomes the contrast between mediæval and modern usage in the more mature music of the later contrapuntal epoch. Palestrina, for example, begins a Stabat Mater as follows: