The following should not be supposed to represent a definitive explanation. The basic position offered is Saussure's linguistics, but some of the ideas belong to Jacobson and Pierce. There are hidden philosophical implications in the definitions, some of which might even be contradictory. Almost all my definitions are over-simplified. Think of these sheets as a help in entering the discourse.
The fundamental philosophic position behind a science of semiotics is that language and history precede the self. We are born into a world where language is already there and history has already decided how language will be used. (This sounds inflexible. If everything is already decided, how can new meanings be generated? The structuralist argument is that history can change the rules, but individuals cannot.)
The Swiss linguist, Ferdinand de Saussure, having lost faith in philology and the historical (diachronic) study of language, argued for studying language as it exists as a system at a particular point in time (synchronically). He argued for dividing language into three levels, langage, by which he meant the human capacity to evolve sign systems, langue, what we think of as a language, such as English or French, and parole, any individual speaker's particular use of the language. Saussure was chiefly interested in langue as an a-historical phenomenon.
A sign is something which stands for something else. The most common signs are words in a language, but traffic signals, punctuation, and visual markers may also be signs. At a broader level, clothing, gestures and even sentences or whole texts may be signs in a larger sign system. In Kurt Vonnegut's novel The Sirens of Titan , the earth and all of human history have been created by a travelling alien to represent a single word: "Greetings," being sent from one super-civilization to another.
Linguistic signs (words)
A spoken language sign is composed of one or more phonemes (material sounds that the voice constructs out of the flow of air across the vocal chords and through the mouth.) The sign may also be represented by graphemes, written representations of letters. A system of graphemes is sometimes called a second-order sign system since it represents the first order system (phonemes.) Phonemes or graphemes may be combined to construct morphemes (syllables or words) and these in turn may be combined to form lexemes (unit of content meaning.) The act of joining morphemes to create units of meaning is called semiosis.
Signs are distinguished from each other by their difference. Thus the sign "dog" is differentiated from "hog," "dig," or "log" by a single letter. The knowledge of any term is dependent on knowledge of the system.
The Binary Nature of Signs:
Signs are composed of two distinct but inseparable parts, the signifier, and the signified.
Signifier: The materially produced representation. DOG
Signified: The mental concept to which the signifier refers. Four- legged barking animal.
The external world
Signs may be transitive, intransitive or transcendental:
Transitive: "dog" refers to an object in the external world.
Intransitive: "and" refers to a grammatical function.
Transcendental: "God" does not refer to a verifiable object in the external world
Signs are arbitrary.
There is no necessary relationship between the sign "dog" and the four legged barking animal to which it refers.
Signs are conventional.
The sign "dog" is understandable only because we have agreed that "dog" will refer to four-legged barking animals. We might have chosen any other combination of letters, "chien" for instance.
The intentionality of signs:
Signs are intentional. They are sent by a sender who wishes to communicate and understandable only to those who understand what is coded in the sign. For instance, smoke in a forest may be nothing more than the indication of a fire, or it may be a sign from one lover to another that the way is clear.
The persistence of signs:
Although signs are arbitrary and conventional, they are always already there. The sign "dog" was arbitrarily chosen before any of us was born, and the agreement that it should represent a four-legged barking animal was made before our arrival. This doesn't mean that it cannot change, only that we cannot individually change it by an act of will.
The slippage of signs:
The relationship between the signifier and the signified is not fixed. Dictionary meanings indicate the most common relationships between signifiers and signifieds in any particular period. Quite often, however, new signifieds alter the meaning of a sign. "Gay" for instance, has recently come to mean "homosexual" rather than "happy." The signified has slipped out from under the signifier. (Language is always engaged in slippage.)
The signifier and the signified: Jacques Derrida points out that the signified is always itself composed of signifiers. Thus my term "four-legged barking animal" operates as the signified of "dog," but is itself a series of signs composed of several signifiers with their own signifieds. In this way, definition is always either infinite or circular.
Semiosis is the arrangement of morphemes into larger units of sense. As such, it functions in two ways. It combines elements syntagmatically in a horizontal relationship of contiguity (makes a sentence) and selects elements paradigmatically in a vertical relationship of selectivity (chooses which signs to use). The term "semiosis" is used quite differently by certain post-structuralists
Semiosis always precedes the fundamental narrative elements mimesis (showing) and diegesis (telling).
Any large arrangement of semiotic units constitutes a discourse. In the broader sense, a discourse consists of the vocabulary, the system of pronounciation, the grammar and syntax and the rules for generating meanings that belong to any group. Thus we may speak of the discourse of the lower class, or the discourse of sports announcers, or the discourse of medicine, or the discourse of fashion. There are no privileged discourses. Another way of saying this is that there is no correct English, no fixed rules about how language may be used. Some discourses are preferable to others under certain conditions, but all discourses are culturally determined, and rely on their power to coerce speakers to enter them.