The long story of the development of music is a continuous and unbroken record of human effort to extend and enhance the possibilities of effects of sound upon human sensibilities, as representing in a formal or a direct manner the expression of man's inner being. The efforts resolve themselves mainly into impulses to find means to produce the effect of design, and to contrive types of expression which are capable of being adapted to such designs. And as the difficulty of coping with two things at once is considerable, men have generally concentrated their efforts on design at one time, and on expression at another. So that some periods are characterised by special cultivation of principles of form, and others by special efforts in the direction of expression ; and owing to the interlacing of various causes in human affairs, these conditions have generally coincided with conditions of society which are adapted to them. The formal character of the music of Mozart's and Haydn's time agrees very well with the character of society in their time; and when a more vehement type of expression became possible the style agreed well with the character of the time, which was specially marked by that impulse to shake off the old conventions which found its most violent expression in the French Revolution.