stratification of material, with individual voices assigned not only their own unique pitch material but texture and rhythm as well, is a key component of Carter's style. His music after Night Fantasies has been termed his late period and his tonal language became less systematized and more intuitive, but retains the basic characteristics of his earlier works. Carter's use of rhythm can best be understood with the concept of stratification. Each instrumental voice is typically assigned its own set of tempos. A structural polyrhythm, where a very slow polyrhythm is used as a formal device, is present in many of Carter's works. Night Fantasies, for example, uses a 216:175 tempo relation that coincides at only two points over its 20+ minutes. This use of rhythm was part of his expansion of the notion of counterpoint to encompass simultaneous different characters, even entire movements, rather than just individual lines. Carter said that the steady pulses of older music reminded him of soldiers marching or horses trotting, sounds no longer heard in the late 20th century, and he wanted his music to capture the sort of continuous acceleration or deceleration experienced in an automobile or an airplane. While Carter's music shows little trace of American popular music or jazz, his vocal music has demonstrated strong ties to contemporary American poetry. He set poems by Elizabeth Bishop (A Mirror on Which to Dwell), John Ashbery (Syringa and Mad Regales), Robert Lowell (In Sleep, in Thunder), William Carlos Williams (Of Rewaking), Wallace Stevens (In the Distances of Sleep and The American Sublime), Ezra Pound (On Conversing with Paradise), and Marianne Moore (What Are Years). Twentieth-century poets also inspired several of his large instrumental works, such as the Concerto for Orchestra (St. John Perse) and A Symphony of Three Orchestras (Hart Crane). Awards and honors 1960: Pulitzer Prize for Music, for String Quartet No. 2 1963: Elected a member of the American Academy of Arts and Sciences 1969: Elected a member of the American Academy of Arts and Letters 1973: Pulitzer Prize for Music, for String Quartet No. 3 1981: Ernst von Siemens Music Prize, awarded by the Bayerische Akademie der Schönen Künste and the Ernst von Siemens Music Foundation 1983: Edward MacDowell Medal, awarded by the MacDowell Colony 1985: National Medal of Arts, awarded by the by President of the United States and the National Endowment for the Arts 1987: Named a Commandeur of