The word chromatic was derived from the Greek, the name of one of the ancient tetrachords, the notes of which were formerly supposed to be similar to the scale known as ‘chromatic’ now.
It is applied to notes marked with accidentals, beyond those normal to the key in which the passage occurs, but not causing modulation.
A scale of semitones does not cause modulation, and is called a chromatic scale, as in the following from the Andante of Mozart’s symphony in D:
Which remains in the key of G throughout; and various chords, such as that of the augmented sixth, and the seventh on the tonic, are chromatic in the same manner.
The following example, from Beethoven’s sonata in B flat (op. 106), is in the key of D:
With regard to the writing of the chromatic scale, the most consistent practice is obviously to write such accidentals as can occur in chromatic chords without changes the key in which the passage occurs.
Thus taking the key of C as a type the first accidental will be D flat, as the upper note of the minor 9th on the tonic; the next will be E flat, the minor 3rd of the key, the next will be F sharp, the major 3rd of the supertonic – all which can occur without causing modulation – and the remaining two will be A flat and B flat, the minor 6th and 7th of the key.
In other words the twelve notes of the chromatic scale in all keys will be the tonic, the minor 2nd, the major 2nd, the minor 3rd, the major 3rd, the perfect 4th, the augmented 4th, the perfect 5th, minor 6th, major 6th, the minor 7th, and the major 7th.
Thus in Mozart’s Fantasia in D minor, the chromatic scale in that key, beginning on the dominant, is written as follows:
in Beethoven’s Violin Sonata in G (op. 96), the chromatic scale of that key is written thus, beginning on the minor 7th of the key:
And the chromatic scale of A which occurs in Chopin’s Impromptu in F major, is written thus:
beginning on the minor 3rd of the key.
The practice of composers in this respect is however extremely irregular, and rapid passages are frequently written as much by Mozart and Beethoven as by more modern composers in the manner which seemed most convenient for the player to read.
Beethoven was occasionally very irregular. For instance, in the last movement of the Concerto in G major he writers the following:
In which the same note which is written A flat in one octave is written G sharp in the other, and that which is written E flat in one is written D sharp in the other. But even here the principal is observable, for the first octave is correct in the scale of G according to the system given above, but having started it so far according to the rule he probably thought that sufficient, and wrote the rest for convenience.
In another place, viz. the slow movement of the Sonata in G (op. 31, No. 1), he affords some justification for the modern happy go lucky practice of writing sharps ascending and flats descending; but as some basis of principle seems desirable, even in the lesser details of art, the above explanation of what seems the more theoretically correct system has been given.