This article considers Milton’s art in relation to modality and the evolving grammar of possibility in Early Modern English. Specifically, it reads the surprisingly complex modal auxiliary verbs, may and its rival can, as keywords in poetic scenes of mental deliberation. A comparative analysis of Shakespearean drama sets the scene, demonstrating how the polysemy of may contributes not only to a psychology of potential action in Brutus’s deliberation over Caesar’s assassination but also to his political conceptions. In Milton’s Sonnet 8, by comparison, the ascendance of ability-can over may affirms the poet’s power and the potential reach of the English language. In the translated epigraph to Areopagitica, genuine liberty finds definition in the interplay of a distinctive English liberty-may with a meritocratic ability can-and-will. Can and will are again lead performers in the deliberative interrogation of divine agency in Paradise Regained, whereas the role of might is questioned in Milton’s tragic depiction of fallen agency in Samson Agonistes.