Critics sometimes divide the plays into approximate chronological groups according to form, theme, motive, and patterns of action. A single criterion may group plays quite sharply (the so-called ‘tragicomic’ IT, Ion, and Hel. of the late 410s, for example); but a second may produce different groupings, or none at all, like the pervasive motif of ‘deliverance’ (below) or attitude to myth. Some plays are ‘out of period’, like the very late, thematically concentrated and formally strict Bacc. In sum, such groupings allow too little to natural or deliberate change in technique, or to reversion to earlier style.

The Troades of 415 nevertheless seems to mark a major divide, probably by accident – an impression increased by its own singularity of composition among the extant plays (are its own content and form, essentially illustrative episodes on the theme of war’s brutality, a function of its final place in the most connected trilogy Euripides wrote?). Before Tro., most plays are tragic or pathetic in tone; after it, lighter or at least ambiguous. Early plays body out major, dominating figures and their protracted agony more consistently than later; contrast Medea, Phaedra, Andromache (name-play) and Hecuba (name-play), with principal characters later: only Heracles (before 415?), Orestes (name-play), Pentheus, Agamemnon (IA) and perhaps Hypsipyle are shown at comparable length and intensity. Also, later plays fill up with persons who compete for attention, often theatrically, and so diffuse interest.