Authentic Modes. Plagal Modes.
The modes were in as far as possible strictly adhered to, but the occurrence of certain intervals difficult to sing and not wholly pleasant to the ear (notably the augmented fourth, or tritone,[64] from F to B), led to modifications or, as we should say, chromatic alterations. B-flat, for instance, was substituted for B whenever the interval from F to B occurred; and later, in the development of part singing, many other alterations were found necessary. Marks indicating such alterations were seldom written in the score, and singers were specially trained to alter intervals at sight, according to the elaborate rules of the practice called musica ficta, or ‘false music.’
We have already adverted to the gradual decline in the use of the Greek language at Rome and the incidental passing from the minds and the memories of men of the alphabetical system of notation which had been inherited from the Greeks. It is not quite clear, however, how the Oriental church, which used Greek until a comparatively late period and even introduced that language into the liturgy of the Latin church, could have absolutely ignored the Greek system of notation. Yet such appears to be the case. As far as we can discover, the early chants of the church, both in the East and in the West, were handed down viva voce, and not until about the eighth century do we find traces of any attempt to devise a system of graphic aids to musical memory. This system, as we first find it, was of a most elementary sort and consisted merely of a few strokes and dashes placed above the text of the song and serving apparently no other purpose than to indicate in a general way the rising and falling inflections of the melody. These signs are known as neumes, and from them gradually developed our modern system of notation. The origin of the neumes is quite obscure. It would appear that at first they consisted merely of the acute and grave accents borrowed from the Byzantine grammarians and designed to indicate the occurrence of a rising and falling inflection respectively. To them were gradually added dashes, strokes, curves, and hooks in various combinations which in time became a fairly complete and precise system of musical writing. Their evolution into the square and diamond-shaped Gothic notation of the middle ages can be followed with sufficient clearness.
Specimen of Notation in Neumes, Tenth and Eleventh Century.
These signs, though representing definite turns and embellishments in the melody, gave no exact indication of pitch. The first sign of anything approaching a staff occurs in the tenth century, when one or two lines were drawn across the page to mark the place of certain tones or pitches. The first line was used for the tone F and the second for the tone C. Other lines were later added for the other tones, and each line was marked with the letter of the tone to which it was assigned. Though all the letters of the scale were used in this fashion, F, C, and G were the ones most commonly employed and from the Gothic characters for these were developed our modern clef signs, as may be seen from the following illustration:
Genesis of Clefs from Gothic Letters.