The linguistic sign
Source: Saussure (1916:77)
According to Ferdinand de Saussure (1916), linguistic signs are bilateral, i.e. every linguistic sign has two aspects which are inseparably connected: the sound sequence (signifier) on the level of expression, and the concept (signified) on the level of meaning. The relationship between the sound sequence and the concept of a linguistic sign is said to be arbitrary, i.e. predetermined by convention only.
In the theory of signs by Charles Sanders Peirce (1931), the linguistic sign is therefore characterised as a symbol. In contrast, Peirce distinguishes two other types of signs, which are not based on convention: indices are identified by a causal relationship between the signifier and the signified, while icons stand in a relationship of similarity to the concept they refer to. As an exception to the basic arbitrariness of linguistic signs, onomatopoeic expressions are naturally motivated. Therefore, they are said to be partly iconic.
In order to illustrate the dependent relationship between sound sequence (symbol), concept (thought) and object of reference in the real world (referent), Charles Kay Odgen and Ivor Armstrong Richards (1923) developed a geometric schema, the semiotic triangle. According to Odgen and Richards, there is no direct relation between symbol and referent: Linguistic expressions relate to the real world only through their meaning.
Source: Odgen/Richards (1923:11)
The structuralist ideas on linguistic signs were partly continued in the school of functionalism. In the Organon model of language designed by Karl Bühler (1934), a linguistic sign serves as a tool by means of which one person communicates with another person about the world. Thus, Bühler distinguishes between three functions of the linguistic sign: It is a symptom that allows a sender to express his own beliefs and feelings (expressive function); it is a signal that appeals to the receiver (appelative function); it is a symbol that refers to objects and states of affairs in the real world (representational function).