The following 12-page essay is an excellent introduction to basic Saussurian/structuralist/semiotic principles in terms of their historical relevance to cinema studies.
I have included hypertext references to CB's Glossary for Students, in order to help explain some technical terms, and some hypertext examples, in order to show parts of this theoretical approach in action.
From: Phillip Rosen, Narrative Apparatus, Ideology. A Film Theory Reader. New York, Columbia University Press. 1986.
Introduction: The Saussurian Impulse and Cinema Studies
At the high point of the so-called structuralist movement (centered in France in the mid-1960s), there was intensive interest in analyzing diverse phenomena investigated in a number of distinct fields (e.g., anthropology, sociology, philosophy, literature, film) by "reading" their objects of analysis through a concept of structure derived from certain aspects of classical structural linguistics. The "linguistic approach" was employed widely, on artifacts ranging from cultural phenomena with obvious bases in verbal language (such as, myth which is verbally transmitted and literary narrative) to those whose linguistic bases are not so obvious. It had a decisive impact in the study of cinema.
One way of explaining the conceptual impact of structuralism is by beginning from a major issue of film theory on which structuralism has had an important effect: the extent to which cinematic signification can be comprehended in terms of a systematics. The elegant and fertile framework for investigating linguistic signifying systems provided by structural linguistics led film theorists to give this question new kinds of attention. In particular, the definitions of linguistic structure of most importance for structuralism generally and film theory in particular stemmed directly from the proposals advanced by Ferdinand de Saussure in his Course in General Linguistics, first compiled in 1915. There Saussure sought to provide the foundations for a modern linguistics, but he also proposed that the conceptual framework he developed might be applied to a general science of signs"semiology." Saussure was not the only thinker to envision such a science, but his distinctions and terminology had a great effect on the attempt to devise first a structuralist and then a post-structuralist cinema semiotics in the 1960s and 1970s. It will therefore be useful to review some of his conceptualizations before outlining some basic issues in cinema semiotics.
Saussure proposed to investigate any language as an abstract, closed system of elements and rules which subtends actual usages of a language and which could generate any number of concrete utterances. The distinction between langue (the underlying system) and parole (the particular utterances) was a fundamental principle of his linguistics because he argued that the first object of  linguistics should be langue. The question then becomes what are the units and relations composing langue.
Saussure calls the basic elements of a language signs. Western thought has generally considered any instance of representation by dividing it into three components: (1) the perceivable material which appears to stand for something else (graphic marks in writing, sonic disturbances of air in speech, etc.); (2) the mental state called up by or associated with that perceivable material ("meaning"); and (3) real-world objects, processes, etc. to which the first two components supposedly correspond or refer. Saussure calls the first (perceivable material) the signifier and the second ("meaning") the signified. For him these are the two inescapable faces of that basic unit of signification, the sign, inseparably joined like the two sides of a piece of paper.
Crucially, Saussure argues that in verbal language the connection between signifier and signified is virtually always arbitrary; that is, while a sign is a unity of signifier and signified, there is no natural connection between the two. In a given usage of verbal language, meaning occurs on the basis of an unconscious but collectively legislated convention of a given tongue, such as French or Chinese. It is only through such conventionalization that signifier and signified can be associated to produce the kinds of suppleness and subtlety of meaning which can be found in verbal expressions. Note that this makes the conception of the signifier more complex than at first appears: a signifier is not just perceivable material which stands for something in the world (a referent) on a one-to-one basis; even if it did this, a signifier also and simultaneously exists as an entity of the group, a collective phenomenon. The sign is therefore a mental entity. (But its basis is not necessarily in consciousness, since language users certainly do not have to be explicitly and consciously aware of the structures of language. )
The premise of the arbitrariness of the sign permits Saussure to conceive of language as requiring a relatively abstract underlying system (langue), for in this account the system organizing signs is what permits meaning to be produced not any inherent characteristics of a given signifier or signified. But a further result of this approach is the conception of such systems as radically closed: Saussure moves to banish concern with the referent from the work of the linguist. The linguist is concerned with reconstructing langue, the unconscious but finite system which is the condition for the possibility of speech (parole). The study of parole cannot in itself be the linguist's goal: there are an infinite number of concrete utterances possible in any tongue; each is caught up in and inflected by concrete speech situations; and any given instance of parole is by itself not systematizable. However, parole can be studied to build inferentially a less concrete entity that logically must subtend it, namely langue.
Saussure's conception of the linguist's objective is thus the construction of an abstract, closed system. This necessitates a number of additional arguments and  methodological propositions, which have to do both with the general characteristics of such systems and with prescriptions for studying them. Among the latter, for example, is the recommendation that language should be studied less in its diachronic (changing over time) aspects than as a synchronic cross-section of a mass of signs and rules for producing understandable utterances. But perhaps the most far-reaching definition Saussure provides is for that of the key relation in the linguistic system, the one which gives definition to the various components of langue: what he names as difference.
Having argued that signs are not determined by their concrete, positive qualities such as a specific relation to a referent but by their position in the system as a whole, Saussure traces out implications. A signifier has linguistic value only in relation to other signifiers, that is, to what in the linguistic system it is not; a sign is defined negatively. On this relational account, signification is determined not just by what is present in an instance of parole, but what is not said, is absent. These negative relations, absences, dominate language.
On a generalized level, Saussure sums up these negative relations with the term difference: language is to be conceived fundamentally as a system of differences among signifiers. The linguist studies differential relations. There are two fundamental axes of such relations, the symtagmatic and the paradigmatic (which Saussure calls the "associative"). The syntagmatic is comprised of the rule-governed relationships among signs present in an actual, concrete signifying "chain" such as a sentence; it is the realm of combination. The paradigmatic is constituted by the relationships among all the possible (therefore implicit, absent) alternatives to each element of a signifying chain; it is the realm of substitution. For example, in the sentence "The big pig ate Nate," at the level of the moneme [linguist.: minimal unit of meaning] the paradigmatic set of adjectives which could fit into the position occupied by big might include small and white, but not from, and still be syntagmatically correct and reasonable ("understandable"), given the relationships permitted by the langue underlying English. Note that both syntagmatics and paradigmatics study the regulation of difference. Individual items of any paradigm or syntagm are distinguished from one another only as clusters of features which can be recognized as pertinent differences, and these vary among different tongues.
Of course, langue is a complex, multileveled system, so such relations would presumably be sought at several levels. Phonology based on these principles, for example, highlights the fact that from the range of possible sounds the human voice can produce, only a limited number signify in a given tongue, and that the relevance of a specific sound is mandated by the collective structure of differences which are pertinent in a given tongue. For example, if the first sound of the English word big is unvoiced rather than voiced, it registers a pertinent phonological difference in the langue of English and becomes pig, another sign with another signified. It is the joining, or articulation of pertinent sounds which form meaningful unitssuffixes, prefixes, words, etc. These meaningful units  achieve their place in language because they can be read through a collective structure of differential relations: big and pig are components of a large system of differences which enables meaning to emerge from such arbitrary signifiers.
There is in addition another linguistic articulation, whereby such meaningful units are in turn joined together into sentences, groups of differentiated words which are ordered according to certain rules and which, according to common sense, express a "complete thought." This "thought" may aspire to the status of anything from an emotional expression of the speaker to a referential description of physical processes. If the "communication" is "successful," then meaning will shine through the network of differences which formed it. This leads to an apparent peculiarity: if, as common sense would have it, language should be used to manifest intended meanings, this occurs by obscuring the basis of languagethe relation of difference. In anticipation of kinds of arguments which will be presented below, we can here point out that one possible conclusion of this account of signification is the contention that meaning is a unifying impulse which obscures the basic heterogeneity of signifying materials and processes which produce it.
In the history of linguistics, Saussure's formulations represent a seminal moment. Their implications can be charted through a number of now classic works, ranging from Roman Jakobson on phonology to Noam Chomsky on syntax. Yet, despite Saussure's own call for a more general semiology based on identical or similar principles, it is not immediately evident that his distinctions are applicable to all kinds of sign processes. Can it be said that all sign systems have as their basic perceivable units arbitrary signifiers? What of visual images, one of our chief concerns here, which so often seem to be based on resemblance to a real-world object? Certainly cinemawhich, because of its utilization of photography and recorded sound, appears at first glance to produce not just representations of reality but presentations from realitymight seem to be poor ground for a Saussurian semiology. How can one argue that cinematic signification is founded on a relational structure of differences? Indeed, in the history of thinking about film, one forceful argument has traditionally been that cinema, by its very nature, depends on a positive relationship to something in the real world, a relationship which is outside any artificial or arbitrary system of image-signs; for if cinema is primarily used as a photographic medium, there must be objects which can be filmed.
Furthermore, suppose there were good counterarguments for the arbitrariness of cinematic signifiers. In itself, this still would not necessarily justify the appeal to linguistic structures as aiding in the understanding of cinematic systematicity. Of course, it may well be possible to argue for the universal validity of categories of verbal langue for understanding signification in general, in part because every normal human being seems to be born with the capacity for language use. This is supported by the fact that language is a central aspect of every human culture of which we know. But such an argument can work in another direction. On  the surface, at least, not all sign systems have such universality; indeed, if cinema is a sign system, it is one which has existed in a very small number of cultures in human history. Conceivably, this could lead to a case that the culturally widespread characteristics of linguistic structure are not comparable to cinematic systems.
Nevertheless, it was precisely Saussure who provided a starting point for the semiological inquiry into cinema which was so important by the late 1960s. Distinctions between cinema and verbal language were taken into account either by new emphases in the conceptualization of cinema or by modifications in Saussurian methodological premises. For example, it proved possible to emphasize a number of "arbitrary" aspects of film images taken as signifiers. If the cinema image is derived through photography from the graphic procedures of Renaissance painters, it can be argued that the basis of the image is a number of conventions of visual representation [see: Quattrocento perspective]. Those conventions turn out to have exemplary importance for the theoretical status of such images. One effect of the argument for the basic conventionality of cinematic image was to open the way for a utilization of the idea of difference in cinematic signification.
We should note here certain
aspects of the influence of conceptions of an underlying langueor
a widespread, fundamental signifying systemfor the
semiological investigation of cinema.
On this question of systematicity, structuralist-influenced analysis made its breakthrough by developing the already existing notion of "classical cinema." This is a concept whose most important use had previously been in the writings of Andre Bazin. It denotes a set of formal and stylistic boundaries defined by a certain fundamental stability of editing and camerawork practices and by certain generic conventions. Taken together these were, according to Bazin, the epitome of Hollywood filmmaking before Citizen Kane. Bazin argued that Citizen Kane and certain other films marked a rupture in film history, after which different constructions of narrative space and time would lead to a more realist approach to the world by means of cinema, which embodied a progressive realization of the latter's ontological nature.
In the two and one-half decades since his death, other theorists, critics, and historiansas often as not unsympathetic to Bazin's phenomenological realist aesthetichave expanded the concept of classical cinema. For some, it does not merely indicate the parameters of form and style in Hollywood cinema of the 30s, but extends roughly from World War I to the breakup of the Hollywood studio system in the 1950s and 1960s, or even to the present, insofar as this system persists through the formal organization of international commercial film and perhaps television in an era when the industry's financial structure is somewhat different. Furthermore, where Bazin might stress the moral significance of film style as an approach to and/or attitude toward reality, other kinds  of thinkers instead stressed the ideological components of these parameters of filmmaking, so intimately linked to the film industry of the most powerful capitalist nation.
Behind this enormous expansion of the concept of classical cinema lies the idea that Hollywood filmmaking has dominated our conception of what a "normal" movie is since the formation of the film studio apparatus between, roughly 191O and the early 1920s. Thus the U.S. film industry can be treated not only as the most powerful economic force among national cinemas, but relatedly as the most influential model of filmmaking practice in history. The claim is that there are certain identifiable parameters of form and style which have for most of film history served as norms and limitations throughout the world, and these norms are associated most closely with the kinds of films produced most successfully and extensively in the American narrative film industry. (While this kind of filmmaking is now often connoted by the appellation "classical cinema," the phrase "mainstream cinema" is sometimes employed with a gain in clarity.)
To anyone who has studied film history, the impact, both economic and aesthetic, of the American film industry will probably seem undeniable. but here we are concerned with another question, namely the search for a systematizable object which will permit the semiotician to formulate something in cinema comparable to langue in verbal language. The investigation of classical narrative cinema, in the extended sense of that term, has provided such an object. Even if we leave aside the question of whether cinema as such has anything strictly comparable to the linguistic system, it is still possible to argue that cinema in its historical actuality has norms so dominant and long-lasting (for a medium less than one hundred years old) that such norms can be treated as the parameters of a system which can hold the methodological place occupied by langue in Saussurian linguistics. This classical system is the basis for what we ordinarily take as understandable, and pleasurable, movies.
Thus, Bazin might argue that ultimately every film image is unique in that it records an absolutely unrepeatable segment of real space and time. But such writers as Raymond Bellour built on certain aspects of the early work of Christian Metz to discover a system of repetitions and regulated differences established both within individual films of the classical cinema and over a large body of films. Further, it was argued by such writers that the paradigmatic orderings of images (and sounds during the greater part of the medium's history) are based on certain identifiable types of narrative organization, with each image and sound answerable first of all to its place in the presentation of a story; that is, every image and sound of classical film responds to certain pervasive narrational principles which regulate the flow of sensations and meanings to the spectator. The norms of signification in cinema would therefore always require some minimum of diegesisa fictional space, time, and worldand diegetic constructions are narrational. Thc attractiveness of this kind of analysis of filmic  narrative and the concept of a dominant or "classical" narrative was further reinforced by the flowering of "narratology" in the study of myth and literature.
A classical text thus becomes identifiable to investigators on the basis of a number of overlapping qualities, not all of which are necessarily present in each instance but which do permit of a certain regulated range of variations. Exemplary headings under which some chief examples of such characteristics cluster indeed: a restricted economy of narrative form; enough stylistic transparency to insure that elements are deployed primarily at the service of plot and character; and a certain recirculation of figures of mise-en-scene, camerawork, editing, and/or genre, both within individual films and through the classical system as a whole. It could even be argued that in superficially non-narrative kinds of films such as documentaries images and sounds are, in many respects, usually organized according to formal and stylistic parameters drawn from classical narrative cinema or at least are most often organized in response to those parameters. There are two emphases of general importance, then, that came from this investigation: first, that signification in cinema is indeed systematizable as a network of structural repetitions and differences; and, second, that a number of conceptualizations from theories of narrative rooted in Saussure can be centrally useful in the semiotics of cinema.
All this might seem of evident utility for the concerns of an academic or esoteric criticism. We now have large-scale generalizations which provide professors with the rationale for microscopic analyses of the patterns of constructing images and sounds in a tremendous number of filmsand hence the basis for a large number of articles in academic journals. However, it is by no means a historical accident that this approach to cinema became so attractive at a time when the institution of the university was a center of directly political concerns. For if there is a system of norms, then we can inquire about the foundations and determinants of such systems, and about the implications of deviation or (from a different perspective) oppositional practices and systems. Further, if the systematic norms of image/sound construction are conceived of as sociohistoric and cultural entities, then so can deviations be conceived of as cultural politics. It is true that this is yet another departure from a strictly Saussurian semiology of cinema, for which a postulated cinematic signifying system would be describable in the same form which Saussure attributes to langue. Not only are the dominant structures underpinning signification seen in historical terms, but now opposition to such structures is contemplated. In Saussurian linguistics such opposition is, strictly speaking, impossible on this side of meaning, for to oppose the structure of langue is to produce non-sense. At most, one may play at the edges of the parameters of the linguistic system, as in certain kinds of poetry and literature.
On the other hand, when attempts were made to develop new conceptualizations of cultural politics in cinema from the earlier tendencies of structuralism and post-structuralism, the Saussurian heritage remained evident. In Saussure  the privileged formal figure is the binary opposition: every term in a signifying system is fundamentally definable only in a relation of difference to that which it is not; that is, in relation to at least one other term. The application of this principle to social and cultural analysis had already been shown as feasible in the analyses of myth, seminal for structuralist narrative theory, performed by the anthropologist Claude Levi-Strauss. By the early 1970s, instead ofor in addition toemploying the figure of the binary opposition as a means of decoding the semantic structure of a text, some of the more politicized cinema semioticians often used it on another level. They differentiated among two classes of films: those which fit clearly into the paradigms of the classical filmmaking system, now seen as integral components of cultural and/or representational systems characteristic of advanced capitalism; and those which opposed classical paradigms of filmmaking. Such formulations of a cultural politics ranged from promotion of certain kinds of avant-garde film making to polemical calls for alternative views of film history which would denaturalize dominant modes of cinematic signification by giving proper importance to other actual or possible practices.
But if the intellectual climate made such a cultural politics attractive, those same impulses could lead to doubts about the ultimate implications of the systemics which was being constructed in film theory. The structuralist-Saussurian tendency in cinema semiotics had put forward a powerful analysis of classical cinema by investigating it as a system; therefore, this tendency included a strong proclivity to reveal a certain fundamental repetition in all films made within this cinema. The years during which these approaches were most aggressively formulated in film theorythe late 1960s to mid-1970ssaw the development and working-out of kinds of political-cultural impulses that not only crystallized in France in 1968, but were felt in varying degrees and through various manifestations in a number of Western nations. In particular, early in this period there was indeed a strong film-theoretical temptation to conceptualize absolutely opposed textual traits as markers of oppositional cinema, for this permitted a political evaluation which supported stylistically radical artistic practices. It is clear that this could and sometimes did lead to the polemical overvaluation of formally defined textual characteristics as being oppositional in themselves. It should be noted, however, that this was part of a more general tendency which opened the way for important explorations. Not only in theory and criticism but also in filmmaking there were important interrogations of the cinematic and cultural potential of textual traits which might be defined as against the classical system of signification (e.g., uneconomical use of elements of narrative form, stylistic and formal opacity, a stoppage of the recirculation of normally repeated figures or a hyperbolization and laying-bare of such recirculation).
This temptation, which we might label binary cultural politics, nevertheless led to difficulties for those who came to structuralist theorization seeking  radically alternative conceptualizations of cinema at the service of an oppositional cultural politics. To treat oppositional filmmaking simply as a radical otherness to dominant practices conceived on a Saussurian model of langue is to attribute to the latter a totalized determining power. That is, from a theoretical standpoint, such a binary sociocultural analysis makes "the" signifying system into a structurally unified totality underlying and penetrating all individual instances of signification within that dominant system. Every mainstream film will ultimately have to be analyzed as being a particular instance of a general totality. The result is a model of signification where analysis is complete when all has been placed structurally within the dominant systemwhich is ultimately only to reproduce that dominance in theory. Analysis of a film or films can cease when its textual complicity is demonstrated.
For those seeking new definitions of a cultural politics, such a totalized, closed system could soon become a critically and politically suffocating premise. Where is transformation, where is history, where is politics in all this? The effects of such totalizing power are located by analysis at the level of practice (the dominant practices are the measure of what shall and shall not be comprehended as disruptive). But as theoretical presumptions, they can mandate a conception that may only be able to demonstrate the impossibility of disruption within the system and consign opposition to a structural place of exterior importance. It becomes difficult to understand where is the political, historical, and/or theoretical common ground on which the two poles struggle and engage with one another.
The desire to conceptualize a cultural politics was only one distinctive strand in the intellectual history of the period. It serves here as an example, one which remained especially important in film culture, of a general set of complex theoretical debates around structuralist conceptions. These discussions were already in progress by the late 1960s, and if we define structuralism in a very strict way (limiting it to the application of Saussurian principles only), the structuralist moment in film theory was relatively brief. Even as that tendency was being forcefully explored in the study of cinema, a number of arguments converged in a general move which did not embody simple abandonment of all interest in systematicity, but did inflect conceptions of signifying systems in crucial ways. Certain aspects of the resulting "post-structuralism" became central to developments in film theory. (In fact, any linear presentation of the development of these arguments can only be heuristic; critiques were most often simultaneous, at least in film theory, with the kind of mobilizations of structuralism discussed above, and the former had effects on the latter.) In particular, conceptions having to do with a "theory of the subject" on the basis of not only semiotic theory but also psychoanalytic and ideological theory, rapidly became central to film-theoretical argumentation.
Here, it is enough to resume our gloss on the concept of signifying system  by pointing out that one central concern of critiques of structuralism involved reconsideration of the structuralist predisposition to treat signifying systems and/or individual instances of texts produced in a given system as relatively coherent totalities. For some critics and theorists, the oppositional utility of structuralist conceptions consisted in part in a challenge to traditional aesthetics, a central aspect of which was said to be the notion of an artwork as a self-contained, organically unified entity. It was thought that the self-sufficiency of the work was put in question by seeing it as a regulated play of differences understandable not in itself but only in relation to the larger system. However, the extraordinary generalizing power which methodology rooted in Saussure confers on analysis of the signifying system (conceptualized on the model of langue) tended to reinstate that unity, redefined and on other levels. Contradiction and heterogeneity could still be shut out in textual analysis, though by placement of the work through the concept of the signifying system rather than at the level of its own uniqueness.
As opposed to this, there developed a predisposition toward suspicion of appearances of unity and totality, whether produced by individual texts being studied or by analysts seeking systematicity. From various perspectives, including psychoanalytic theories of signification and social theory, it was argued that contradiction as well as unity, heterogeneity as well as homogeneity, might be a goal of analysiseven the analysis of a relatively well-developed signifying system. In fact, this claim could actually be presented from the perspective of semiotic theory as deriving from certain of Saussure's conceptions, and hence as an internal critique of Saussurian structuralism. It may be true that the "experience" of many instances of signification is that of a finalization, a completion of meaning and hence a unity; and if so, one might argue that "experience" is rooted in a greater totality which can be called "signifying system." But if we follow Saussure in conceiving of all signs as defined by a structure of differences, then signification is the action of difference. Stopping analysis when one has unified that action under the rubric of meaning would thus be to participate in the finalization, and actually to contribute to the obfuscation of fundamental signifying mechanisms.
This leads to the possibility that words such as structure and system, if they are to be retained, should not be theorized as completely closed and totalized entities. Let us accept for now the validity of describing a film text as "classical," and let us suppose that such a text is read, in the first instance, as an individual polished unity or with an implicit awareness of a general signifying system. Neverthelessor even because of thisit may be that theory and critical analysis should read such texts more deeply and aggressively, seeking the processes of difference and disjuncture which produce that sense of unity. This would be to ask how surface homogeneity occurs on the basis of heterogeneous components rather than, as it were, accepting the text and/or signifying system at their own word.  Thus, it becomes conceivable that over and above the analyzable totalities and unities imposed by a signifying system, a certain "excess" can be found even in the most classical film. Then it becomes possible that critical analysis may be able to discover cases of films produced within the classical system but which nevertheless take some of its mechanisms to such an extreme that the film exceeds certain of the aspects which seem to unify it. This kind of argument can be made on a number of levels ranging from that of perception [...] to ideology (as in a famous collective reading of Young Mr. Lincoln performed in 1970 by the editors of Cahiers du cinema, who found a number of crucial moments where the logic of the film's ideological project breaks down into contradiction and incoherence [...].
This type of argument necessitates a fundamental complexity in the conceptual framework of any postulated cinema semiotics. Most simply, we can note here one major consequence. The goal of abstracting a closed system of signification that directly comprehends all individual film texts by describing their processes as being either inside or outside that system must be transformed. Elements which appear excessive, heterogeneous, incoherent from the perspective of a purportedly totalized signifying system and/or apparently "unified" text must be accounted for. And the means of suppressingor repressingthem must be included in the description of a purported totality. This is not simply to reject systemic investigation of signification, but it is minimally to begin from a more complex view of the regularities of filmic signification. For many important film theorists, lines of argument such as this necessitated appeals to other kinds of explanatory and investigative frameworks.