In this essay I argue that Thesis II (that 'Man must prove the truth, i.e. the reality and power, the this-worldliness of his thinking in practice') from Marx's Theses on Feuerbach, might be read as a cogent theory of poetry, and that the 'proof' of a line of poetry lies in the reader's uptake of it. In support of this claim, I give examples from the critical practice of Robert Hass as having particular resonance with the thesis; and move on to give examples of the reality and power of poetry (or its lack) through my own critical readings of poems by Emily Dickinson and Australian poets, John Kinsella and Jennifer Harrison. [Author's abstract]