Sharps and flats were invented because composers found it necessary to use other tones than those that could be represented by the staff degrees in their natural condition. The history of their origin and development is somewhat complicated and cannot be given here, but it should be noted once more that it was the need of expressing more than could be expressed by the older symbols that called forth the newer and more comprehensive method. The use of sharps and flats in key signatures grew up early in the seventeenth century. In the earlier signatures it was customary to duplicate sharps or flats on staff degrees having the same pitch-name, thus:
. (The use of the G clef as here shown did not of course exist at that time.)
The double-sharp and double-flat became necessary when "equal temperament" (making possible the use of the complete cycle of keys) was adopted. This was in the time of Bach (1685-1750).
Signs of expression (relating to tempo and dynamics) date back at least as far as the year 1000 A.D., but the modern terms used for this purpose did not appear until some years after the invention of opera, the date given by C.F.A. Williams in Grove's Dictionary being 1638. These words and signs of expression were at first used only in connection with instrumental music, but were gradually applied to vocal music also.
Other systems of notation have been invented from time to time in the course of the last two or three centuries, but in most cases they have died with their inventors, and in no case has any such system been accepted with anything even approaching unanimity. The tonic-sol-fa system[40] is used quite extensively in England for vocal music, but has gained little ground anywhere else and the chances are that the present system of notation, with possibly slight additions and modifications, will remain the standard notation for some time to come in spite of the attacks that are periodically made upon it on the ground of cumbersomeness, difficulty in teaching children, etc. The main characteristics of staff notation may be summed up as follows:
1. Pitches represented by lines and spaces of a staff, the higher the line, the higher the pitch represented, signs called clefs at the beginning of each staff making clear the pitch names of the lines and spaces.
2. Duration values shown by shapes of notes.
3. Accents shown by position of notes on the staff with regard to bars, i.e., the strongest accent always falls just after the bar, and the beat relatively least accented is found just before the bar.
4. Extent and description of beat-groups shown by measure-signs.