The first publication of the prolific and unorthodox early modern writer Margaret Cavendish (1623–1673) versifies the atomist underpinnings of the cosmos in imitation of Lucretius's great first-century BCE atomist poem, De rerum natura. However, soon after the publication of the 1653 Poems and Fancies, Cavendish claimed to have "Wave[d] the opinion of Atoms." Following her cue, critics have generally either ignored or maligned the atomist poems, downgrading the status of Lucretianism and poetry alike in the Cavendish corpus. In this article, I argue that although Cavendish does abandon the idea that inanimate particles constitute the fundamental structure of matter, she never forswears the fanciful Lucretian epistemology she develops in Poems and Fancies. Closely attuned to the intersection between epistemological skepticism and poetic bravado in De rerum natura, Cavendish's atomist poetry amplifies the elements of Lucretian atomism that bring it into conversation with skepticism. Agreeing with Lucretius that nature's inner truths are fundamentally unknowable, Cavendish establishes fancy as a legitimate speculative practice. By pitting her fanciful poetics against scientific methodologies that make claims to truth, Cavendish establishes ignorance as a defensible epistemological posture. Her manipulation of gender stereotypes in her showy modesty and ostentatious professions of flightiness and ignorance is essential to this goal. She subverts the conventional modesty topoi that are so central to early modern women's writing in order to establish epistemological modesty—skepticism—as the hallmark of genuine natural philosophy.