The philosophical ideal of coherence — the requirement that a body of beliefs or a narrative form a consistent, mutually supporting whole — is enacted in the long poem's ambition to create a unified vision, though modernist long poems (the Cantos, "The Waste Land") famously both aspire to and fail to achieve complete coherence; Coleridge's theory of the organic poem — in which the parts mutually condition and support the whole — is a philosophical claim about coherence: the great poem achieves a coherence that is not imposed but grown; A poet working in a traditional form (sonnet, villanelle) accepts the formal constraints as the scaffolding of coherence — rhyme, meter, and conventional structure ensure that the poem hangs together as a unified whole; The New Criticism's valorization of unity, irony, and tension as poetic virtues is grounded in a philosophical ideal of coherence — the poem that holds contradictory elements in tension achieves a higher-order coherence than one that simply asserts a single position; Postmodernist poetry explicitly challenges the ideal of coherence as an ideological construct — the demand for coherent narrative and argument is seen as a disciplinary mechanism that silences heterogeneity and suppresses contradiction; In the philosophy of truth, the coherence theory (truth as internal consistency of a belief system) is implicitly enacted by poets who build elaborate, self-consistent mythological systems (Blake's Prophetic Books, Yeats's "A Vision") as alternatives to the incoherence of the external world