"My own experience of art has forced me to accept most of the standards of taste from which abstract art has derived, but I do not maintain that they are the only valid standards through eternity. I find them simply the most valid ones at this given moment. I have no doubt that they will be replaced in the future by other standards, which will perhaps be more inclusive than any possible now."

- Clement Greenberg, "Towards a Newer Laocoon."

Opsis, Melos and Lexis are the three mediums in a triad that both determines and is prefigured by the history of all media theory. However, throughout this history, these three mediums have been part of a variable economy, each either being privileged above the others, or not at all, based on the function and role of the media in different periods. Otherwise figured in corresponding triads such as Image, Music, Text and Symbol, Index and Icon, the different functions of these three mediums are first laid out in Aristotle's Poetics. While Aristotle's account of the three mediums is couched in his theory of the mixed medium of the theater, he orders the triad according to their mimetic, or imitative, capacities. Aristotle's mimetic structure is informed by his conception of the medium as being an obstacle to the real or immediate, and his belief that a medium should be transparent. The variable economy of the triad is thus predicated on the prevalent notion of representation in a given era.

Critics like Northrop Frye have articulated a collapse of these mediums into each other in the arts. In frameworks such as his, the salient features of a particular medium may appear in another medium. For example, Melos appears in Lexis as the melodic or rhythmic element in poetry. And yet, though Frye's analysis embodies what is, for some, a needless blurring of the three categories, it still belies the view that each medium has its own essential character.

In the history of media, there have been opposing tendencies both to maintain the schism between Melos, Opsis and Lexis, and to recognize their interdependence. In Laocoon: An Essay on the Limits of Painting and Poetry, Gotthold Lessing asserts an intrinsic difference between painting and poetry, or rather, word and image. His analysis reveals an intrinsic panic at the blending of mediums, presaging the turn toward medium specificity ostensibly embodied in avant-garde and abstract art. Clement Greenberg emphasizes the importance of aesthetic purism, attempting to "police the borders" between mediums (Mitchell, 55). However, the fluctuating economy of the triad gestures too much towards the changing notions of art and representation to cleave it too cleanly into separate mediums.

In his Poetics, Aristotle outlines a taxonomy of the mimetic arts, articulating how the process of mimesis or imitation is enacted by man. Aristotle's conception of mimesis and its functions runs counter to Plato's pejorative view of the arts as a poor mirror of reality. Rather, Aristotle considers mimesis to be entirely natural: "Imitation is natural to man from childhood, one of his advantages over the lower animals being this, that he is the most imitative creature in the world, and learns at first by imitation" (Aristotle, 627). Poetry arises both from this natural human predilection for imitation, and from the natural pleasure derived from mimetic works. Moreover, according to Aristotle, the most realistic modes of representation are the most enjoyable to the spectator, since these types of mimesis "gather the meaning of things," offering the opportunity to learn about reality (Aristotle, 627). Poetic mimesis, however, does not merely mimic human life, but should aim at representing and understanding the universal causes of human action.

The proximity to the real or to the immediate emerges as one of the most important facets of Aristotle's account of mimesis. Aristotle organizes drama based on the relationship between representation and the real. Tragedy is not, like Comedy, an imitation of persons, but of action, which Aristotle considers to be closest to reality. In Aristotle's poetic structure, his first concern is with the object of representation; representation itself is secondary to that being represented. As such, when Aristotle outlines the six key components of the poetics of tragedy, he constructs a mimetic hierarchy, privileging Mythos (Plot or Fable) over the other five aspects. He orders these components according to their significance in the poetics of tragedy: Mythos (Plot or Fable), Ethos (Character), Dianoia (Thought or Themes), Lexis (Diction), Opsis (Spectacle), and finally, Melos (Melody).

Melos, Opsis and Lexis are a triad of mediums that traffic in the explicitly performative aspects of drama. Of these three, Aristotle locates Lexis as being more the province of the poet than Opsis and Melos, which are less artistic and less necessary to the mimetic function of tragedy. Requiring a degree of poetic craft, Lexis or Diction, in Tragedy, is the means through which meaning is conveyed in words. It hinges on an assumed concordance between words and their meanings, and is meant to complement the Plot, Character and Thought of a Drama. Aristotle relegates Opsis, or the visual aspect of a performance, to a secondary position. Believing that the visual constituent of a performance was the work of the mask-maker rather than the poet, Aristotle believed in the mimetic, if somewhat extraneous, function of Spectacle. Either Aristotle wrote very sparely of Melos, given its reduced status in his framework, or he confined the majority of his discussion to the second book of the Poetics, which did not survive. However, he suggests in the Poetics that like Opsis, Melos or Music in Drama is an nonartistic enterprise, though it is the most pleasurable for spectators.

The hierarchy instituted by Aristotle, where Lexis precedes Opsis and Melos, strictly mirrors his view of mimesis' role in human experience. Where the telos of Aristotelian mimesis is to bring humanity closer to the real, Antonin Artaud reconceives the performative aspects of theater to upturn this telos. In his conception of theater and its function, Artaud inverts the relationship between mimesis and reality, positing the capacity of theater to subsume reality. He refigures the very idea of mimesis, suggesting that the role of the theater is not to accurately represent reality to the audience, but rather to affect the audience in as guttural a manner as possible. Artaud puts forward 'The Theater of Cruelty' as his model for altering the relationship between representation and reality:

Neither Humor, nor Poetry, nor Imagination means anything unless, by an anarchic destruction generating a fantastic flight of forms which will constitute the whole spectacle, they succeed in organically calling into question man, his ideas about reality, and his poetic place in reality. (Artaud, 245)

Artaud's goal is to dramatically alter the relative position of the audience to the stage. Unlike Aristotelian tragedy, imitation is no longer the point, since that affords some space between spectator and spectacle; Artaud's 'theater of cruelty' closes that gap and attempts to provoke communication between the "two closed worlds" of the stage and the auditorium (Artaud, 250).

Artaud's inversion of Aristotle's characterization of mimesis requires a corresponding reversal of order in the hierarchy of Lexis, Opsis and Melos. Indeed, for Artaud, Melos and Opsis, embodied in the most sonorous sounds and affective, jarring lights and visuals, are the most important features of theater: "That is why in the 'theater of cruelty' the spectator is in the middle and the spectacle surrounds him. In this spectacle, sound effects are constant: sounds, noises, cries are chosen first for their vibratory quality, then for what they represent" (258). Indeed, representation is entirely secondary in Artaud's framework, as evinced by his account of the role of Lexis in the theater: "To change the function of speech in the theater is to use it in a concrete and spatial sense, and in combination with everything in the theater that is spatial and of significance in the concrete realm" (Artaud, 270). Speech operates primarily as evocative sound, prior to attaching to some meaning. In this way, the very idea of representation in mimesis sits on the periphery, accidental to the theatrical process.

Artaud's revision of Aristotelian poetics, while generally maintaining the segregation of Melos, Opsis and Lexis, allows a synaesthesia of sorts, as he converts speech, a temporal art for Aristotle, into a spatial one. The conflation of spatial and temporal, of word and image, problematizes Aristotle's metaphysical framework of mimesis. Opsis, supposedly a provocation for the eye, and Melos, for the ear, are collapsed into each other through the history of media, especially in such terms as Horace's ut pictura poesis. This triad has not remained only in the realm of the theater, and the capacities of each to mean and to represent has been examined across many mediums. Northrop Frye, in the Anatomy of Criticism, flattens Melos and Opsis into Lexis, writing: "Considered as a verbal structure, literature presents a lexis which combines two other elements: melos, an element analogous to or otherwise connected with music, and opsis, which has a similar connection in the plastic arts" (Frye, 244). In his essay "Rhetorical Criticism: Theory of Genres," Frye studies how melody and spectacle operate through poetic device. Though Aristotle might suggest that Frye is dealing exclusively with Lexis here, it appears impossible to parse the relationship between representation and reality without recourse to the trinity of Melos, Opsis and Lexis.

Resistance to the kind of medium blending Frye addresses in his theory of genres is embodied in the theoretical and practical turn toward medium specificity, which is predicated on the notion that ach medium has its own proper character. Clement Greenberg builds on the idea of this sui generis character in his essay "Towards a Newer Laocoon," where he posits abstract art as being the best of the modern plastic arts, since it utterly engages with the notion of medium purism. Greenberg follows Aristotle's hierarchy, conceiving of music as being more remote from imitation than image and text, but attends to the disentanglement of mediums from each other. In his view, the dominant art of any given period will legislate the creation of all other arts, such that "the subservient ones are perverted and distorted; they are forced to deny their own nature in an effort to attain the effects of the dominant art" (Lessing, 24). Where Aristotle sought to make mediums as transparent as possible with mimesis as his goal, Greenberg characterizes the Aristotelian ideal of art as illusion, and suggests that "the mistakes" of art can only be solved through purism and the opacity of the medium: "The arts, then, have been hunted back to their mediums, and there they have been isolated, concentrated and defined. It is by virtue of its medium that each art is unique and strictly itself. To restore the identity of an art the opacity of its medium must be emphasized" (32). Greenberg's artistic paradigm, with pure form as its ideal, then serves a different goal than Aristotle's, and exemplifies a historical shift that Greenberg sees as inevitable.

Greenberg recognizes that his account of medium specificity, which calls for rupture between the categories of Melos, Opsis and Lexis, emerges as the result of a historical trajectory. Roland Barthes exerts more pressure yet on the triad in his aptly titled collection of essays Image, Music, Text, studying the status of each medium as a sign system. In such essays as "Rhetoric of the Image," "Musica Practica," "Lesson in Writing" and "The Grain of the Voice," Barthes assumes a level of equivalence between the three mediums, suggesting that each produces meaning in its own way: "Language, according to Benveniste, is the only semiotic system capable of interpreting another semiotic system...How, then, does language manage when it has to interpret music? Alas, it seems, very badly" (Barthes, 179). While Barthes does not privilege medium specificity as currently superior to other modes of artistic production, he does stress here that the three different mediums produce meaning in distinctive ways. And yet, in "Word and Image," W.J.T. Mitchell demonstrates the impossibility of clearly differentiating between how text and image, or Lexis and Opsis, construct the relationship between representation and reality. Rather, he examines the apparent divide between these mediums as emerging from larger social and cultural questions.

Ultimately, Melos, Opsis and Lexis seem to exist as a symbiotic collective of mediums, the distinction between them a construct contingent on extant critical and aesthetic beliefs about what purpose art and the media should serve. It is thus more useful for media theory to concede the fluidity between these mediums, and to conceive of them as a triad.