Eliot also made significant contributions to the field of literary criticism, strongly influencing the school of New Criticism. While somewhat self-deprecating and minimising of his work—he once said his criticism was merely a "by-product" of his "private poetry-workshop"—Eliot is considered by some to be one of the greatest literary critics of the twentieth century. The critic William Empson once said, "I do not know for certain how much of my own mind [Eliot] invented, let alone how much of it is a reaction against him or indeed a consequence of misreading him. He is a very penetrating influence, perhaps not unlike the east wind."
In his critical essay "Tradition and the Individual Talent", Eliot argues that art must be understood not in a vacuum, but in the context of previous pieces of art. "In a peculiar sense [an artist or poet] ... must inevitably be judged by the standards of the past." This essay was an important influence over the New Criticism by introducing the idea that the value of a work of art must be viewed in the context of the artist's previous works, a "simultaneous order" of works (i.e., "tradition"). Eliot himself employed this concept on many of his works, especially on his long-poem The Waste Land.
Also important to New Criticism was the idea—as articulated in Eliot's essay "Hamlet and His Problems"—of an "objective correlative", which posits a connection among the words of the text and events, states of mind, and experiences. This notion concedes that a poem means what it says, but suggests that there can be a non-subjective judgment based on different readers' different—but perhaps corollary—interpretations of a work.
More generally, New Critics took a cue from Eliot in regard to his "'classical' ideals and his religious thought; his attention to the poetry and drama of the early seventeenth century; his deprecation of the Romantics, especially Shelley; his proposition that good poems constitute 'not a turning loose of emotion but an escape from emotion'; and his insistence that 'poets... at present must be difficult'."
Eliot's essays were a major factor in the revival of interest in the metaphysical poets. Eliot particularly praised the metaphysical poets' ability to show experience as both psychological and sensual, while at the same time infusing this portrayal with—in Eliot's view—wit and uniqueness. Eliot's essay "The Metaphysical Poets", along with giving new significance and attention to metaphysical poetry, introduced his now well-known definition of "unified sensibility", which is considered by some to mean the same thing as the term "metaphysical".
His 1922 poem The Waste Land also can be better understood in light of his work as a critic. He had argued that a poet must write "programmatic criticism", that is, a poet should write to advance his own interests rather than to advance "historical scholarship". Viewed from Eliot's critical lens, The Waste Land likely shows his personal despair about World War I rather than an objective historical understanding of it.
Late in his career, Eliot focused much of his creative energy on writing for the theatre, and some of his critical writing, in essays like "Poetry and Drama," "Hamlet and his Problems," and "The Possibility of a Poetic Drama," focused on the aesthetics of writing drama in verse.