slightly different picture, the preface to the second edition of The Sound Shape of Language argues that this book represents the fourth stage in "Jakobson's quest to uncover the function and structure of sound in language." The first stage was roughly the 1920s to 1930s where he collaborated with Trubetzkoy, in which they developed the concept of the phoneme, and elucidated the structure of phonological systems. The second stage, from roughly the late 1930s to the 1940s, during which he developed the notion that "binary distinctive features" were the foundational element in language, and that such distinctiveness is "mere otherness" or differentiation. In the third stage in Jakobson's work, from the 1950s to 1960s, he worked with the acoustician C. Gunnar Fant and Morris Halle (a student of Jakobson's) to consider the acoustic aspects of distinctive features. The communication functions Influenced by the Organon-Model by Karl Bühler, Jakobson distinguishes six communication functions, each associated with a dimension or factor of the communication process [n.b. – Elements from Bühler's theory appear in the diagram below in yellow and pink, Jakobson's elaborations in blue]: Functions referential (: contextual information) aesthetic/poetic (: auto-reflection) emotive (: self-expression) conative (: vocative or imperative addressing of receiver) phatic (: checking channel working) metalingual (: checking code working) One of the six functions is always the dominant function in a text and usually related to the type of text. In poetry, the dominant function is the poetic function: the focus is on the message itself. The true hallmark of poetry is according to Jakobson "the projection of the principle of equivalence from the axis of selection to the axis of combination". Very broadly speaking, it implies that poetry successfully combines and integrates form and function, that poetry turns the poetry of grammar into the grammar of poetry, so to speak. Jakobson's theory of communicative functions was first published in "Closing Statements: Linguistics and Poetics" (in Thomas A. Sebeok, Style In Language, Cambridge Massachusetts, MIT Press, 1960, pp. 350–377). Despite its wide adoption, the six-functions model has been criticized for lacking specific interest in the "play function" of language that, according to an early review by Georges Mounin, is "not enough studied in general by linguistics researchers". Legacy Jakobson's three principal ideas in linguistics play a major role in the field to this day: linguistic typology, markedness, and linguistic universals. The three concepts are tightly intertwined: typology is