In Paradise Lost the reciprocal forces of ‘first matter’ are centrally located in ‘Light Ethereal, first of things’, ‘that light’, as Raphael explains, that is constituted from its inhering ‘reciprocal’ forces. This study argues that the workings of this Miltonic reciprocity were first understood in concrete specificity by Immanuel Kant, though buried on two intricately argued manuscript pages of his Opus postumum. Almost as remarkable as Kant’s Miltonic recognitions, William Wordsworth – directly inspired by earlier Kantian ideas of reciprocity and of the sublime – made his own way to this Miltonic poetics of co-existent being, most spectacularly in The Prelude. In this fascinating study, Budick demonstrates how Milton, Kant and Wordsworth together offer a revolutionary understanding of the function of poetry in the quest of human consciousness for participation in being.