PERIOD. A Period is one of the divisions which characterise the form of musical works, especially in such as are not very elastic in construction, as Tunes and Airs; and, frequently, the main subjects of large works in their simple exposition. It is common to find in these a first division ending with a half close followed by one ending with a full close, as in this example from Beethoven's Sonata, op. 109:—
These together are held to constitute a period, and the lesser divisions are phrases. A complete tune is often composed of two or three such periods, and such examples may be taken as types: but in fact periods must be exceedingly variable in structure. Sometimes the subdivisions into lesser members may be difficult to realise, and in others they may be subdivisible into a greater number of members of varying dimensions. A period is defined by some writers as a complete musical sentence, and this gives sufficiently well the clue to identify wherever it is desirable to do so.
