Empson is today best known for his literary criticism, and in particular his analysis of the use of language in poetical works: his own poems are arguably undervalued, although they were admired by and influenced English poets in the 1950s. The philosopher Ludwig Wittgenstein was an acquaintance at Cambridge, but Empson consistently denied any previous or direct influence on his work. Empson's best-known work is the book "Seven Types of Ambiguity", which, together with "Some Versions of Pastoral" and "The Structure of Complex Words", mines the astonishing riches of linguistic ambiguity in English poetic literature. Empson's studies unearth layer upon layer of irony, suggestion and argumentation in various literary works, applying a technique of textual criticism so influential that often Empson's contributions to certain domains of literary scholarship remain significant, though they may no longer be recognised as his. The universal recognition of the difficulty and complexity (indeed, ambiguity) of Shakespeare's Sonnet 94 ("They that have power ..."), for instance, is traceable to Empson's analysis in "Some Versions of Pastoral". Empson's study of "Sonnet 94" goes some way towards explaining the high esteem in which the sonnet is now held (often being reckoned as among the finest sonnets), as well as the technique of criticism and interpretation that has thus reckoned it.