nature and allocation of the arias to the different roles in opera seria was highly formalized. According to the playwright and librettist Carlo Goldoni, in his autobiography, The three principal personages of the drama ought to sing five arias each; two in the first act, two in the second, and one in the third. The second actress and the second soprano can only have three, and the inferior characters must be satisfied with a single aria each, or two at the most. The author of the words must [...] take care that two pathetic [i.e. melancholy] arias do not succeed one another. He must distribute with the same precaution the bravura arias, the arias of action, the inferior arias, and the minuets and rondeaus. He must, above all things, avoid giving impassioned arias, bravura arias, or rondeaus, to inferior characters. By contrast, arias in opera buffa (comic opera) were often specific in character to the nature of the character being portrayed (for example the cheeky servant-girl or the irascible elderly suitor or guardian). By later in the century it was clear that these formats were becoming fossilized. Christoph Willibald Gluck thought that both opera buffa and opera seria had strayed too far from what opera should really be, and seemed unnatural. The jokes of opera buffa were threadbare and the repetition of the same characters made them seem no more than stereotypes. In opera seria the singing was devoted to superficial effects and the content was uninteresting and stale. As in opera buffa, the singers were often masters of the stage and the music, decorating the vocal lines so floridly that audiences could no longer recognise the original melody. Gluck wanted to return opera to its origins, focusing on human drama and passions and making words and music of equal importance. The effects of these Gluckist reforms were seen not only in his own operas but in the later works of Mozart; the arias now become far more expressive of the individual emotions of the characters and are both more firmly anchored in, and advance, the storyline. Richard Wagner was to praise Gluck's innovations in his 1850 essay "Opera and Drama": " The musical composer revolted against the wilfulness of the singer"; rather than "unfold[ing] the purely sensuous contents of the Aria to their highest, rankest, pitch", Gluck sought "to put shackles on Caprice's execution of that Aria, by himself