Language, as we have created and defined it, is any codified system of symbols used by a group of people with the intent of communicating a message.  These symbols can be letters and words, either written or spoken, or gestures ranging from a wink to ASL.  The essence of language by these terms lies in a balance between its three key components, metaphor, metonymy, and syntagm (Lacan).
The signifier, or the sound used to convey a meaning (either in actual speech or in our thoughts) assosciated with the signified, or the meaning itself, synthesize to form the linguistic sign, i.e., a sound with no associated meaning is not a sign, and a meaning with no associated sound is not a sign (Saussure).  In the process of communication, we conceive an idea and speak or write the symbol or series of symbols that we associate with the idea; it is important to see, then, that a word as a symbol is a metaphor.  Any word, 'ice' for example, as a sound or written word, is representative of the communicator's idea of what 'ice' means, the communicator's relative interpretation of an object or action or idea.  This sound or scribble could mean anything; it is only functional for communication in its differentiation from another symbol within an agreed system, and its function is reliant on not only the implied associations of either its user or its receiver but also by its syntactical relationship to other symbols used with it.  "The dog jumps" and "The jumps dog" do not mean the same thing, despite using identical symbols, because of their sequence in relation to one another, and the effectiveness of communication is dependent on who is saying it to whom (i.e., the former would be more appropriate if used between two spectators at a pet show, the latter more appropriate if used colloquially between snowboarders on the slopes).
The relations between linguistic signs are associative in the 'library' of the mind as vocabulary, and syntactic in use; in formulating discourse, a word which is chosen has associative relation to words which were not chosen, and then given a sequential relation to the words which were chosen before and/or after it.  Saussure claims that the linguistic system is defined by opposition; between ideas and ideas, sound-images and sound-images, but "without positive terms."  This is to say that a linguistic sign is more closely representative of that which all other signs within its system are NOT representative of than it is representative of its signified idea.
To what limit, then, is the extent of the formalization of the system of symbols?  To what degree is it necessary to agree on the exact terms of a symbol?  There are no exact terms of the symbol; the symbol is relatively representative of an idea, and yet it is necessary to reach a compromise between signified and signifier that is mutually understood.  These compromises can only be reached by using symbols to describe symbols (such as, "ice is either solid water, a diamond, to kill somebody, to apply a cold compress, to frost a baked good, etc." and by inferring its representation.  A letter is a tool in this way: to communicate linguistically is to assemble a framework using units that are individually without representation other than a sound, i.e., the letters 'a' and 't' do not represent anything other than noises in and of themselves, but "a" as a word and their union as "at" does, however, only in relation to another juxtaposed construction, such as "a thing" or "be at," and so forth.
My argument is that the linear nature of the linguistic sign, syntax, stems not from some inherency of language but rather from the convention of universally codifying a set of symbols.  It is important to look at purpose when considering construction, and the purpose of all language is communication - a means to this end was structuring sound and gesture, and in structure there is invariably sequence.  It becomes necessary to make a clear distinction between syntagm, or the various relationships between units that comprise a whole, and syntax, the sequencing of these units, in order to qualify as language a means of communication which has, as of yet, been classified as an engimatic and isolated entity all its own, mystical and frivolous, the means of communication that is the work of art.
First, allow me the room to define art as an expression of sentiment that is necessarily designed to be interpreted by an audience.  One draws doodles in a notebook and these are not works of art, but the same exact doodles in a gallery would be.  This is proof of the necessary aspect of art that is communication and interpretation; the work is a symbol for an idea, a metaphor, and this metaphor has metonymy, but including art as language shows the component of syntagm that is syntax, or the associations between sequencing the units comprising the whole, is not a necessary components of language if art is a language, because art does not necessarily have syntactic relation between its structural units (i.e., brush strokes, chisel scrapes, clay pinches, torch weldings, etc.), unless this relation is chosen to be implied by the artist, as in creative writing, cinema, or music, or other such mediums where the audience is subjected to a sequence.  An artist choosing a sequenced medium is effectively just choosing another symbol, using sequence not for universal codification but as an extension of the symbol itself; I will get into this in further detail later on.
People often appreciate the "pretty sound" of a foreign language without knowing anything of its syntactic relations, only its sound and inflections, which are metaphors, since they are sound symbols with relative meanings that are being interpreted as something else entirely that is pleasant, albiet termless and without a compromised meaning.  The same can be said of art in the cliched expression "I don't know art, but I know what I like."  This is proof that an admirer of an expression does not necessarily understand the syntctic relations of units forming the expression as a whole (the constructive process) but that as an audience of a communication they still appreciate the expression as a whole as "pretty," "harsh," etc.
Saussure shows us the arbitrary nature of the linguistic sign, that signified meaning is not "linked by any inner relationship" to its signifier sound, and this is evident in the existence of different languages using different words to represent the same meaning (such as tree, arbor, deryevo, albero, baum, etc.).  Each of these signifier sounds has the same value, but the metonymies related to each term are reliant on the respective word system they are confined to.  Art, as a language, is subjected to the same rule.  A work of art is a series of symbols, only without strictly defined terms.  Without completely formalizing the symbols, less emphasis is placed on clarity of meaning and more emphasis is placed on individual interpretation; in effect, the purpose of the message being communicated shifts away from trying to present a universal concept and towards encouraging examining the notion of the presented concept itself.  To say in conversation "flowers are weak," I must assume already that my audience will agree on what a 'flower' is, on what I mean by 'weak,' and using these symbols can then interpret my assertion; however, their interpretation will already be a compromise of meaning, since we have already compromised individual meaning to agree on what a 'flower' is or what 'weak' is without actually getting into their ideas.  In conversation, this would seem to be true; it is impractical to theorize on personal associations of ideas to ideas, symbols to symbols, if the purpose of the communication is to reach a quick and mutual understanding.  When we listen to conversation, we listen in order to understand the speaker; we assume there is meaning in the sounds (although these meanings are arbitrary, and relative) and our mental process is one of interpretation and inference.  A willing audience of artistic expression is precisely the same symbol presentation, expectant of interpretation and inference, but one in which the individual approach of interpretation is encouraged in order to associate symbols more closely with their related values - at the expense of absolute value.  The fundamental difference between a scientific dissertation about nuclear fusion and a meticulously researched but fictional novel about nuclear fusion is that the dissertation by design is expected to seen as static, universal information, and the novel by design is expected to be seen as relative information to be interpreted relatively, even if both manuscripts contain the same information.
To further commit art to the realm of language, consider therapeutic works.  Art therapists are trained to recognize the nonverbal symbols and metaphors that are communicated within the creative process, symbols and metaphors which might be difficult to express in words or in other modalities.  These difficulties not only can occur, but are likely to, especially considering mental disorder, conditions which even if articulated adequately by sufferers cannot be accurately expressed verbally, especially to one that is not a sufferer.  The word "depression" does very little justice to the condition, other meanings of the word being to be pushed in, or recessed.  The common association of depression is with being 'very, very sad,' and sufferers of depression know that this is not case; to express the value of the condition to a richer extent some are encouraged to "write" or "paint" what they feel.  This reinforces my argument that the failings of language to communicate lie in exploring relative meaning, since universal meaning is already assumed by convention of codification; through art, an individual can try to express a value in his or her own context with minimal reference to an external standard.  An audience member hears the word "depression," having never heard it, and knows nothing of it other than that it exists.  It is explained in conversation to be "a mental condition characterized by melancholia, lack of motivation, high anxiety, and irregular sleep patterns."  The associations one then makes concerning depression are based on the values of the symbols assigned to ideas of melancholia, amotivation, etc., and so depression is defined only by related values, without establishing the value of depression itself.  Now, if the same audience member were to encounter a painting done by a sufferer of depression entitled "depression," having never encountered depression, is in this situation actually presented a value for the symbol, but one that is not universal.  Continuing to view a gallery of paintings, all entitled "depression" and all different, the observer synthesizes each of these symbols into a total concept of depression, though this concept is still dually relative, contingent upon both artist and audience.
If language, as described by Saussure, is a codification of metaphors and metonymies without positive terms, and if art, as I describe it, is creating a positive term from metaphors and metonymies without universal codification, it now becomes necessary to make certain qualifications and address the issues which arise from recognizing art as language.  I should make a differentiation between 'language' and 'linguistics,' since in this new light the one that exists (that linguistics is the scientific study of language) is insufficient, and, considering that I have shown syntax is not a necessary component of language, incorrect.  'Linguistics' should rather be defined as the study of codified language, or methods of communication that adhere to a universally recognized system, rather than of all language; 'language,' in turn, is any general medium of communication involving metaphor, metonymy, and syntagm.  By allowing this distinction we can differentiate communication from language, art from linguistics, and still categorize both art and linguistics as language, for the purpose of delineating the benefit of the interplay between art and linguistics as alternate means to the same end: communicating an idea.
I have established the focus and failings of both art and linguistics in their approaches to communication, and comparing the two we are presented with an obvious symbiosis in their successes, in creating value and in universalizing it.  I do not intend to imply that art, as a creative process, is not structured, but rather that its syntagm is not to unversalize it, lacking syntax, but to expound on its symbolic representation.  The exception to this is when an artist chooses to use structure to convey a meaning, most obviously in cinema, writing and music, but in these instances of art the structure is not a measure for universalizing the message so much as it serves as another symbol within the message itself.  The difference between a pantoum and a limerick, an opera and a concerto, as art forms, is only structure, in fact, but these structures are chosen to be used by the artist because the structure is recognized by the artist to be a symbol in and of itself - effectively, a medium is picked (such as oil on canvas, sculpted bronze, string vibrations, etc.) as a symbol in order to assign value to a symbol.  This is different from the linguistic system, in which the medium (English, Russian, French, etc.) is the constant that universalizes a symbol's representation.  Evidence of this is reached by considering the relationship between 'a painting,' or what structurally defines what a painting is, as a general symbol, and 'the painting,' or the qualities that define a specific work of art.  'A painting' is an application of a staining agent to something; 'the painting' is the metaphor and metonymy of the symbol of 'a painting.'  
Special note must be made of art that uses linguistics as it's symbolic medium, since in most of these cases it becomes exceedingly difficult to separate the structure of the medium from the structure of the.work itself.  It is easier to answer the question "what is a painting," than it is to answer the question "what is a poem," for example, since a painting as a symbol has a clearer distinction between its universalizing structural components and its symbolic components.  In creative writing the symbols used are meant to be interpreted syntactically, with sequential association, and so it becomes more difficult to tell where 'a poem' ends and 'the poem' begins; that is, the separation between structure of the symbol medium and the symbol value is purposely blended.  The purposes of choosing these mediums are varied and relative, at artist's discretion, and an artist as a representer of value is confined only by capacity and exposure, relative ability to communicate and experience with social structure.
Mentioning purpose, linguistics, and poetics, I would be remiss to not refer to Roman Jakobson's Linguistics and Poetics:
'Sometimes we hear that poetics, in contradistinction to linguistics, is concerned with evaluation.  This separation of the two fields from each other is based on a current but erroneous interpretation of the contrast between the structure of poetry and other types of verbal structure: the latter are said to be opposed by their "casual," designless nature to the "noncasual," purposeful character of poetic language.  In point of fact, any verbal behavior is goal-directed, but the aims are different and the conformity of the means used to the effect aimed at is a problem that evermore preoccupies inquirers into the diverse kinds of verbal communication.'
It follows that, considering this and what has been established above, the distinction between poetics and linguistics is merely a matter of differing approach to the same end, which is communication.  What separates a poem from a few paragraphs is that the structure of the paragraphs is used to universalize the communication to compromise a meaning quickly between the communicator and the audience, and the structure of the poem is used by the communicator to emphasize the representation of the symbol in a relative way (dactyllic meter to soothe, spondees to punctuate, long lines to to lead, short lines for unease, etc.).  Experience and/or education in art conditions the audience to be aware of what they are "supposed" to feel from a representation, that is, the intended message of the artist in a work of art, just as those who do not understand Russian can appreciate its aural aesthetics, and even without formal training can eventually understand certain expressions simply by exposure and interpretation.
Recognizing art as language makes it easier to understand criticism.  It answers the question of why there is no apparent descrimination between literary studies and criticism (Jakobson) in showing that there is one, but it is only seen when separating the linguistic from the artistic.  Literary studies focuses on examining the structure of art, the codifications chosen to be employed by the artist and its relation to a literary work as a symbol, whereas the realm of criticism is in synthesizing audience interpretation and artist's intent - literary study can (and should) be used as a tool of effective criticism, but they are still different approaches in semiotics.
It is impossible to assess effectiveness without considering purpose, for how can something be effective if it serves no function?  Let us observe and describe the effect of "successful art" upon the audience and assume that what occurs from "successful art" through the reaction of the audience is the purpose, which seems a fair assumption, even if an over simplification, since both artist and audience are satisfied by "successful art."  This "successful effect" can be referred to as katharsis, from the Greek, translating into either clarification, purification, or purgation; there are enthusiasts and dissenters for each translation, but my interpretations are that all three are integral to the purpose of art: the successful artist imitates an idea and produces a representation of it, and in doing so, purifies or refines aspects of the idea seen as needing emphasis, purges the 'foreigness' of the idea by confronting it, and through this purification and purgation the artist and audience both get a clarification of the idea.  In this manner it can be said that purgation deals with the scope of an idea (the size and perspective of it governs the aspects of the work the artist and audience are confronted by, i.e., a work of art cannot deal with what is not presented by it, either actually or in implications such as a title or caption) and that purification deals with the focus of an idea (in refining the facets that are represented, the artist no longer affects what is being presented so much as how what is being presented is synthesized or interpreted).
The role of the "good" critic, then, is to promote the universal accessibility of a work of art without obscuring the original representation.  In producing the work the artist confronts the idea to purge the ignorance of it, to create a value for it, and in being presented to the work the critic does the same.  The effective critic should concentrate on the purification of the idea, then, because the 'angle of approach,' or desired boundaries of an artwork, as it were, are part of the purgation and is the artist's domain - the critic must correctly interperet the idea an artist seeks to purge the 'foreigness' of and instead of altering the perceived original idea should endeavor to focus more clearly upon it.
  The difficulty in criticism lies in the discretion between the focus and scope of a work of art: it is the artist's prerogative to provide the scope of a work with enough focus to represent the idea in a way that can be recognized accurately by the critic - it is the critic's duty to accurately recognize the scope represented and to analyze and improve the focus so as to make each audience member's relative synthesis as close to the artist's original represented idea as possible.  Every artist, however, and also every critic, has their own unique perspective.  The first and foremost goal of the critic is appreciation; if a critic does not attempt to understand the representation, no conclusions about the effectiveness of the work can be made.  Relative perspective cannot be avoided, as it shapes all synthesis, but a critic must be wary and willing to recognize what appeals specifically and what appeals to the audience.
In summation, linguistics and art are different means to the same end, which is communicating an idea.  They differ in their extent of codification and in their focal points, but by recognizing these differences and accepting both methods as valid communication we can compare and use art and linguistics together to explore either approach in order to further evaluate language, which is a unifying characteristic of mankind.