"Radical Matter" argues that expansive and experimental mixed mode poetic works since the American mid-century embody a language-based materiality that motivates the valuations of their symbolic economies. I focus on three works--William Carlos Williams's Paterson, Bernadette Mayer's Studying Hunger Journals, and Juliana Spahr's Well Then There Now--that each engage prose alongside verse, material from other texts and authors, or multiple discursive modes: all ways, I argue, of substantiating the desires and rhetorical strategies that orient these speakers in language and in relation to their imagined addressees. These substantiations bring forward features and consequences of language's articulations as discourse--whether lyric, narrative, epistolary, diaristic, or other--that carry out metaphoric interventions in the crises of value that drive these poetic works towards their substantial lengths, their material and modal inclusivity, and the speakers that they voice. I read Paterson's larger strategy of textual bricolage and its local junctures between prose and verse as expressions of the portability of lyric discourse's sensory and semantic functions. The circulations and evolutions of lyric figures and phrasal units throughout the work act in opposition to the expressive and libidinal paralyses of the stagnant American economic and social body that the poem's matter documents. Against the reifications of established forms--aesthetic forms as well as the institutions and conventions that organize social life--Williams manifests language's broadest functional value through the material resources of lyric. The discursive junctions of Bernadette Mayer's Studying Hunger Journals activate the rhetorical relations of lyric, epistolary, and diaristic address as sites where speakers and addressees materialize as embodiments of the pronominal figures "I" and "you." I test these materializations against psychoanalytic and structural linguistic models of subject formation in order to read Mayer's drive towards atemporality and the indeterminacy of her interlocutors in terms of the personal history her journals document. Through the materializations and dematerializations of grammatical persons, Mayer rehearses the lack and losses that motivate her hunger and which the operations of language make manifest. In my last chapter, I read Spahr's collection of prose, verse, and prose poetry, Well Then There Now, in terms of its orientation towards difference as the material consequence of her opaque plural pronominal lyric protagonists "we" and "they" and her transparent first person prose speaker, as well as the intertextual reading that her multi-mode collection demands. I argue that Spahr's materialization of difference and the readerly exclusions it enacts constitutes an anti-pluralist resistance to rhetorical demands of readerly identification and inclusivity with poetic speakers. The "matter" of Spahr's works--personal, political, environmental, and economic systems of interrelation and complicity--becomes "radical" by virtue of a rhetoric that manifests difference as the fundamental condition of language and the requisite term in active, self-organized reading.