One of the main points the book makes is the prevalence of the "proper meaning superstition" and the fact that there can be no serious discussion of the philosophy of language prior to its abolition. The proper meaning superstition is [such a fallacy] that every word has one exact meaning and that this meaning is part of the word. According to the authors, meaning does not reside within the words but within the humans using them.
To explain their concept of the relations between referent (what a word is used to refer to), symbol (a word) and reference (the connection between symbol and word referent, i.e. the interpreter), the authors introduce the model of a semiotic triangle. In this triangle, each of the three related entities (referent, symbol and interpreter) is assigned an edge: Referent in the lower right-hand corner, symbol in the lower left-hand corner and the reference on the top of the triangle. The most fundamental proposition of the book can be reduced to the assertion that there this triangle does not have a basis: There is no direct connection between referent and symbol (contrary to the proper meaning superstition). Symbol and referent are only related through an interpreter, who translates the symbol into a referent or vice versa.
... the authors go on to analyze sign-situations in general and symbol-situations in particular. A sign is a natural representation of something that exceeds the sign (a barking sound may be a sign for a dog, for instance). A symbol, on the other hand, is a special kind of sign: It does not have a natural connection to its referent (unlike normal signs), but only a purely conventional one: The word "dog" is only connected with dogs because it is used to refer to dogs. Were the word "madgs" used to refer to dogs, the word "dog" would have no connection whatsoever with a dog.
The first thing to consider when talking about language is thought, simply because their there is no use of language without thought. The special case of thought that must be examined before language can be dealt with is the interpretation of signs - the interpretation of symbols is only a special sub-case of this activity.
The interpretation of signs is [simply] "our psychological reaction to it [the sign], as determined by our past experience in similar situations, and by our present experience" (p. 244). So when we hear a dog barking, we assume that it is a dog because in our past experience the barking sound has generally been accompanied by the existence and close proximity of one of these creatures. The same interpretative process applies for symbols.
The problem found in communication is the fact that there is no direct relation between referent and symbol, making the interpretation the central aspect of communication. [...]
... there are definitions that do not mean anything and therefore act purely as irritants, supporting a particular orator simply by confusing his audience. Such irritants must be recognized and ignored.
... there are two important functions of language: The strict symbolization, in which facts are transferred from one to another. And the evocative or emotive use of language, which aims to promote certain emotions and feelings within the listener. The confusion of these two has been responsible for much of the discussions and controversy between scientists and poets.