A just conception of this broad scheme of Brahms's ideal and of his thoroughness in working it out is necessary, we must insist, not only to appreciation of the man himself, but to any true understanding of his relation and service to music. Brahms was enabled, by the tireless training to which he subjected his fertile and many-sided genius, to couch romantic feeling in classic form. In order to grasp the full significance of such a work, it is necessary to bear in mind those fundamental principles of musical effect and facts of musical history which have been presented in the Introduction. Music has resulted from the gradual formal definition, by time and pitch relations, of those vague gestures and utterances by which men expressed their primitive feelings. It has been, in a word, the product of two human instincts, neither of which alone would have sufficed to produce it--the instinct for expression and the instinct for beauty. But these instincts have not worked with precisely equal efficacy at all times. In fact, so limited is human attention, so few things can men attend to at once, every great development of expression has generally disturbed the equilibrium requisite to beauty, and every great advance in beauty has generally, for the time being, restrained the eloquence of expression. Musical history is a series of reactions between man's primal emotional impulse and his desire for intelligibility. First, urgency of feeling drives him to a formless cry; then the wish to be understood and the love of beauty induce him to formulate this cry; finally, as soon as the formula is felt to be inadequate to further expression, it is discarded in favor of one more elastic and complex. The conventions that are helpful at one stage prove hindrances in the next. The same forms that subserve growth up to a certain point, beyond that point hamper it. Accordingly, in the history of music, formulation has always been followed by relaxation of the formulæ to admit of new expression; and when new expression has been thus evolved, a new and more complex form has had to be worked out to regulate and fix it.