The poetic function, states Jakobson in “Linguistics and Poetics”, “by promoting the palpability of signs, deepens the fundamental dichotomy of signs and objects”.  It tends to obscure the referential function of the message and is oriented instead on the message itself; therefore similarity at sequence level is the fundamental norm, or, in Jakobson’s words,
|the poetic function projects the principle of equivalence from the axis of selection into the axis of combination. (39)|
Besides, poetry is characterized by a parallelism at all linguistic levels, from the phonological to the syntactic one. The study of the poetic function should not be restricted by the structuralist critic to poetry, but should encompass instead all art messages and be included in the overall context of semiotics. However, Jakobson’s main approach to poetry was linguistic, and that preference can be clearly seen in the analysis, co-authored with Lévi-Strauss, of Baudelaire’s Les chats.
As Jakobson wrote in an essay entitled “Poetry of Grammar and Grammar of Poetry”, the structuralist’s goal was that of describing “the selection, distribution and interrelation of the diverse morphological classes and syntactic constructions” in the poem, and this type of analysis revealed “striking symmetries and antisymmetries, balanced structures, efficient accumulations of equivalent forms and salient contrasts”,  in other words the exquisite interrelations among the constituents of the poem. Lévi-Strauss and Jakobson’s close analysis of Les chats emphasizes the value of the text as an “absolute object”: this value is due to the complex modulations of its units, be they syntactic, rhetorical or, especially, phonic.  In a polemical response to the study of Les chats,  the American critic Michael Riffaterre called in question the validity of its authors’ approach, which is based on the delineation of four structures within the sonnet:  1. a tripartite division (quatrain I, quatrain II, sestet), defined by grammatical and metric models; 2. a bipartite division (octet vs. sestet); 3. a chiasma-like division, relating quatrain I to tercet II, and quatrain II to tercet I (in which the cats appear as objects and, respectively, subjects); 4. a system which envisages the sonnet as an open structure, made up of two sestets, separated by a distich. Riffaterre does not belie the existence of these structures and interplays, but in the chapter “The Irrelevance of Grammar” of his essay he questions their equal contribution to the poetry of the text: not all linguistic symmetries are literarily active in the poem, as a purely “technical” reading may suggest. Therefore the receiver of the poetic message should also be taken into account, and in that sense Riffaterre coins the term ”superreader”, denoting a fictitious person who should have the advantage of “screening pertinent structures and only pertinent structures”. (38) Riffaterre mentions that the “superreader” in this particular case is composed of: Baudelaire himself, commentators of the poem, including Jakobson and Lévi-Strauss (when they “deviate from the method”), a Larousse dictionary, other notes and other informants, and so forth; thereby he departs from pure structuralism in so far as he takes into consideration also the historical context of the work, and the response of his sensitive reader. However, his celebrated critique of Jakobson’s method is not lacking in arguments: “no grammatical analysis of a poem can give us more than the grammar of the poem”, he contends, (36) and an evenhanded search for contrasts and parallelisms leads nowhere, while it betrays a mere “belief in the intrinsic explanatory worth of purely descriptive terms”. (33)
If in Riffaterre’s response there are revealed the interpretive limitations of the pure structuralist method, as it was used in a “happily positivistic” mood by Jakobson and Lévi-Strauss, other concepts and principles propounded by these early structuralists gained ground in the course of time and became widely spread tools in the analysis of poetry. One such example is David Lodge’s discussion, in The Modes of Modern Writing (1977), of Jakobson’s metaphor/ metonymy binary, and the ensuing analysis of some poems by Philip Larkin from this perspective. Though poetry is an inherently metaphoric mode, Lodge contends, Larkin can be regarded as a “metonymic poet” (which does not mean that he uses no metaphors at all).  “The Whitsun Weddings” is a classical example of Larkin’s technique: he foregrounds the metaphors “against a predominantly metonymic background, which is in turn foregrounded against the background of the (metaphoric) poetic tradition”. (216)
A STRUCTURALIST POETICS proper was not formulated however before 1975, when Jonathan Culler published his influential study bearing that title, where he attempted to adapt the French type of structuralism to the American critical tradition. In the first place the source of Culler’s concept of “literary competence” can be found in Chomsky’s generative model (where linguistic competence is opposed to performance), rather than in the older Saussurean distinction between langue and parole. As the sequence of sounds “speaks” to the listener only if he possesses an internalized grammar, that is the implicit knowledge of a language’s inner system, so a text acquires a structure and a literary meaning only when it is read in a particular way: the reader brings to it an “implicit understanding of the operations of literary discourse which tells one what to look for” (SP 114). In Culler’s view, anyone who has not internalized the “grammar” of literature would be baffled if he encountered a poem, because he would be unable to convert the linguistic sequences into literary structures. Culler admits that it is difficult to find the exact place where linguistic competence ends and literary competence begins, because “literature is a second-order semiotic system”. (SP 114) The fact that one can understand the language of the poem can be proved by that person’s ability to translate it into another language, but understanding the poem means at least the ability to provide a thematic synthesis of it. Culler insists on the special conventions for reading poetry which the reader has to acquire and to master, such as: 1. the rule of significance: reading the text “as expressing a significant attitude to some problem concerning man and/or his relation to the universe”; (SP 115) 2. the rule of metaphorical coherence: assuming a sense of coherence at the levels of both the tenor and the vehicle; 3. inscribing the text in a poetic tradition: this code provides a set of symbols and types with universal meanings; 4. the convention of genre, which provides norms that classify texts into categories; 5. the rule of totality, stipulating coherence at all levels; 6. the rule of thematic unity ascribed to the text: oppositions of all kinds can be arranged within symmetrical binary structures.
All these codes and conventions make up the concept of literary competence and are the basis of the institution of literature.
It is by now obvious that in Culler’s theory one can distinguish a second difference from earlier structuralist principles, that is the shift of emphasis from the text to the reader, the competent reader, as he calls that construct (compare with Riffaterre’s superreader): the structure resides basically in the reader’s competence, which ascribes it to the text in the act of interpretation. Later on another American critic, Stanley Fish, will take up this concept and move the structures of meaning entirely out of the text into the scope of the readers’ community.
Anyhow it can be observed that in the studies of some later structuralists, such as Riffaterre, Culler, or Prince, communal conventions of interpretation superseded the individual reader’s analytical endeavors. They were less interested in “what actual readers happen to do /than in/ what an ideal reader must know implicitly in order to read and interpret works”, as Culler admitted. (SP 123-4) This novel perspective upon the location of meaning and the best approach to it is the common ground where structuralism met with Reader-Response Criticism, as well as a major starting point for the deconstructive post-structuralist initiatives, which Jonathan Culler, among other former structuralists, would incorporate into his later studies.
Looking at structuralism in retrospect, whether in the interpretation of poetry, or in the study of narratives, or in the description of texts in general and of other cultural products, one cannot help observing how far it is, though not very remote in time, from the present-day skepticism towards anything stable and central in whatever kind of textual structure. In a postmodern “quantum universe”, as some thinkers define the contemporary world, a single determinate meaning appears to be impossible to attain, and the binary opposite, with the alleged identity of, and the absolute difference between, terms, is no longer a valid instrument for defining cultural reality, as hard-core structuralists would firmly believe. Instead, the unstable, self-subverting structures of our post-Einsteinean reality are best described by concepts such as relativity, uncertainty, or discontinuity: the following chapter will deal precisely with this rupture in the evolution of the traditional logic of determinate binary structures.
 In D. Lodge (ed.), Modern Criticism ..., 37-38. Hereafter cited parenthetically in the text.
 “Poetry of Grammar and Grammar of Poetry”, in Roman Jakobson, Language and Literature (ed. K. Pomorska and St. Rudy, 1968), 127.
 The latter emphasis echoes the importance that Russian formalists attributed to the role of sound in poetic texts.
 “Describing Poetic Structures: Two Approaches to Baudelaire’s ‘Les Chats’” (1966), in J. Tompkins (ed.), Reader-Response Criticism ... Quotation pages are given parenthetically in the text.
 Here is the transcription of Les chats, in the original: Les amoureux fervents et les savants austères/ Aiment également, dans leur mûre saison,/ Les chats puissants et doux, orgueil de la maison,/ Qui comme eux sont frileux et comme eux sédentaires.// Amis de la science et de la volupté,/ Ils cherchent le silence et l’horreur des ténèbres;/ L’Erèbe les eût pris pour ses coursiers funèbres,/ S’ils pouvaient au servage incliner leur fierté.// Ils prennent en songeant les noble attitudes/ Des grands sphinx allongés au fond des solitudes,/ Qui semblent s’endormir dans un rève sans fin;// Leurs reins féconds sont pleins d’étincelles magiques,/ Et des parcelles d’or, ainsi qu’un sable fin,/ Etoilent vaguement leurs prunelles mystiques.
 D. Lodge, The Modes of Modern Writing ..., 214. Next quotation cited parenthetically in the text.