By making beautiful "mistakes," Beethoven has extended the rules of composition. Ries relates, "During a walk I took with him, I spoke to him of certain consecutive fifths which occur in his C minor Quartet, Op. 18, and which are so eminently beautiful. Beethoven was not aware of them, and maintained that I must be in error as to their being fifths. As he was in the habit of always carrying music paper with him, I asked for it, and wrote down the passage in all its four parts. When he saw that I was right, he said, 'Well, and who has forbidden them?' Not knowing how to take this question, I hesitated. He repeated it, until I replied in astonishment, 'But, they are against the first fundamental rules!' 'Who has forbidden them?' repeated Beethoven. 'Marpurg, Kirnberger, Fuchs, etc., etc.--all theorists,' I replied. 'And I permit them!' said Beethoven." The harsh beginning of Mozart's C major Quartet (No. 6 of the set dedicated to Joseph Haydn) has been the subject of fierce attacks and controversies. Many musicians have supposed that misprints must have crept into the score; while others have endeavoured to prove in detail that all the four instruments are treated strictly according to the rules of counterpoint. Otto Jahn (in his 'Biography of Mozart,' Vol. IV. p. 74) finds it beautiful as "the afflicted and depressed spirit which struggles for deliverance." This may be so; and it is needless to conjecture what the admirers of the passage would have said, if it had emanated from an unknown composer. As it stands, it is, at any rate, interesting as an idea of Mozart, whose compositions are generally distinguished by great clearness of form and purity of harmony. The adherence to a strictly prescribed form may easily lead the composer to the re-employment of some peculiar idea which he has already employed in a previous work. In fugues especially this may be often observed. Beethoven, in his sonatas, and likewise in his other compositions written in the sonata form, as trios, quartets, etc., introduces not unfrequently in the modulation from the tonic to the dominant certain favourite combinations of chords and modes of expression; and he has one or two phrases which may be recognised with more or less modification, in many of his compositions. Mozart, too, has his favourite successions of chords; for instance, the interrupted cadence which the German musicians call _Trugschluss_. Spohr repeats himself perhaps more frequently than any other composer. Mendelssohn has a certain mannerism in the rhythmical construction of many of his works, which gives them a strong family likeness. Weber has employed a certain favourite passage of his, constructed of groups of semi-quavers, so frequently, that the sight of a notation like this:-- [Music] is to the musician almost the same as the written name Carl Maria von Weber.