No branch of modern music is more characteristic or more illustrative of prevailing tendencies than the solo song, for none illustrates more clearly the relation between music and the thought expressed, or the aim of the musician to be guided by the idea rather than the conventions of classical form. The typical modern song has only become possible through the long development of the resources of art, and only through long experience and innumerable experiments have men learnt what to do and what not to do in dealing with a poet's language. Songs existed from the beginning of musical time; but until the beginning of this century they consisted either of regular definite tunes which had to be fitted to all the verses, whatever change of sentiment or accent occurred; or of formal consciously artistic products like opera arias. Many tendencies combined to bring about the close wedding of music to word and sentiment, which began to be adopted at the beginning of the present century. Gluck's theories had some influence, for they caused people to pay more attention to the meaning of the words and the declamation. The development of instrumental resources and of pianoforte technique put fresh powers in the hands of composers. Mozart and Haydn both approached to the ideal of modern song here and there, and Beethoven in several cases actually attained it.