The mediaeval development of musical notation has an important bearing on the history of music as an art. It brought music into direct contact with the graphic arts and must have helped to suggest that the melodies written in a book were no less beautiful and no less permanent than the pictures which illustrated the text. The monks who invented notation in order to preserve liturgical music intact and uncorrupted from the vain errors of sinful man did as a matter of fact thereby provide him with the means of developing his error scientifically. It occurred to someone that secular music could be recorded in notes as well as sacred. The alphabet ceased to be practically a monopoly of the Church. The social status of the musician rose as soon as notation made it clear that the composition of a piece of music could be a thing apart from its performance. When music can be read from notes its hearers inevitably begin to realize that the individual performer has no exclusive property in it. His voice may have lost none of its thrill, but the listener knows now that interpretation is not the same thing as spontaneous creation. If a song or a dance tune is thought worth the trouble of writing out, it means that it is held to be worth preserving. The musician who made it begins to take rank with the learned clerk instead of being classed with tumblers and acrobats, rogues and vagabonds. The cultured amateur makes his appearance in the ages of chivalry. Music, considered as a fine art, belongs to the privileged classes alone. No doubt the illiterate people had their songs and dances, but the ordered progress of musical development was of necessity carried on mainly by those who could read and write. It is in this period that the musical styles of East and West are sharply differentiated by the discovery of the principle of harmony. Harmony, the simultaneous sounding of two or more different notes, is so indispensable a part of music to-day that many people find it almost impossible to conceive of an art of music based on melody alone. The most unlearned are so accustomed to the sounds of harmonic music that although their natural instinct inclines them first towards pure melody it may be doubted whether they can recall an ordinary tune without at least some vague half-conscious recollection of a harmonic basis to it. This suspicion is confirmed by the fact that many tunes have become widely popular in which the melody has at moments no significance apart from the underlying harmonies.