Vaihinger's philosophy of "as if" — the theory that human cognition operates through useful fictions, constructs that are known to be false but are nonetheless practically necessary — has directly influenced Stevens's concept of the "supreme fiction," the poem that we know to be constructed yet willingly inhabit; The philosophical question of whether literature's fictionality is a deficiency (it is not literally true) or a virtue (it enables a kind of truth-telling unavailable to literal description) runs from Plato's expulsion of the poets to Sidney's "Defence" to contemporary theories of narrative; A poet working with persona or dramatic monologue might reflect philosophically on fictionality — the fact that the poem's "I" is a fiction, not identical with the biographical author — and on the strange truth-claims that fictional persons can make; Searle's speech act philosophy distinguishes between sincere assertions (where the speaker genuinely claims truth) and pretended assertions (in fiction), and this philosophical distinction informs debates about whether the lyric "I" makes sincere or fictional claims; Kendall Walton's "mimesis as make-believe" — the theory that fiction involves a sophisticated game of make-believe governed by rules about what we may "imagine-true" — provides a philosophical account of how readers engage with the fictions of poetry; Aristotle's claim that poetry is more philosophical than history because it deals with the universal (what could happen) rather than the particular (what did happen) is a defense of fictionality — the poem's invented world is philosophically more revealing than any actual event