Ashbery's works are characterized by a free-flowing, often disjunctive syntax; extensive linguistic play, often infused with considerable humor; and a prosaic, sometimes disarmingly flat or parodic tone. The play of the human mind is the subject of a great many of his poems. Ashbery once said that his goal was "to produce a poem that the critic cannot even talk about". Formally, the earliest poems show the influence of conventional poetic practice, yet by "The Tennis Court Oath" a much more revolutionary engagement with form appears. Ashbery returned to something approaching a reconciliation between tradition and innovation with many of the poems in "The Double Dream of Spring", though his "Three Poems" are written in long blocks of prose. Although he has never again approached the radical experimentation of "The Tennis Court Oath" poems or The Skaters and "Into the Dusk-Charged Air" from his collection "Rivers and Mountains," syntactic and semantic experimentation, linguistic expressiveness, deft, often abrupt shifts of register, and insistent wit remain consistent elements of his work.