This article studies a Euripidean innovation: the introduction into tragic language and the subsequent (selective) usage of the expression oὐκ ἂν δυναίμην by Euripides. This negative potential optative appears sixteen times within the surviving Euripidean corpus, as a stereotypical syntactic structure that is intertwined with dramatic content and meaning. But, surprisingly, this expression is absent from Aeschylus, Sophocles, and all other tragedians. Through close reading of the sixteen Euripidean cases, the article traces and defines the conspicuous context of this expression: oὐκ ἂν δυναίμην is uttered by high-status individuals (for example, members of a royal family), when they envisage the impossible/unattainable in present and future within an intensely emotional atmosphere (ranging from hatred and loathing to agonising grief and despair), during pivotal moments of the play. Metrical convenience is also served, as the expression covers the first five elements of the iambic trimeter.