Seneca's plays, probably not intended for stage presentation, were literary exercises following the models of Greek tragedy and more especially of Euripides. By the humanist, after he had acquired some slight knowledge of the classical theatre, they were naturally accepted as plays actually performed, and their artificial and elaborate diction, which is their most conscious departure from Attic standards, was eagerly appraised as a merit. Their themes, with the exception of that of the pseudo-Senecan "Octavia," are borrowed from Greek mythology, with a strong preference for the most sensational and bloody stories of adultery, incest, the murder of parents by their children or of children by their parents. Whatever the revolting and bloody details, crime and its retribution make up the burden of each story. The plays present only the last phase of an action, and consequently open with lengthy exposition of preceding events. Much happens behind the scenes, little on the stage; there are many narrative and lyrical scenes, comparatively few dramatic. In comparison with the Athenian tragedies, they seem like prolonged rhetorical discussions of the familiar legends. Their structure involves a division into five acts, which had probably been earlier adopted in Latin tragedy and is noted in the "Ars Poetica," and the exclusion of the chorus from any participation in the action. It appears usually after each of the first four acts and indulges in philosophical reflections, hymns in praise of some deity, or lamentations. In each play a chief person or hero can be distinguished in conflict with one or more chief opponents; and each of the leading persons is accompanied by an adviser or confidant, usually a faithful friend for a hero and a nurse for the heroine. In addition to mortals, supernatural visitants, furies, gods, and especially ghosts, have a prominence that stirred Elizabethans to imitation. Though the presentation of character is not humanly vital, the long speeches and soliloquies display an elaborate analysis of moods of passion, with an absence of Athenian religion, a pagan cosmopolitanism, and an almost modern introspection. The style and philosophy were the chief recommendation of the plays to the Renaissance taste. Artificial, with constant use of antithesis, stichomythia, and hyperbole, oratorical, sonorous, bombastic, and thickly sprinkled with aphorisms and sentiments, the style seemed to the humanists to reach the height of tragic elevation and philosophic sententiousness.