The linguistic unit is a double entity, one formed by the associating of two terms. Instead of uniting a thing with a name, the linguistic sign untes a concept with a sound-image.

The word "concept" is replace by the word "signified," while the word "sound-image" is replaced by the word "signifier." The signified and the signifier together make up the sign.

Two basic principles: 

1) The arbitrary nature of the sign--The sign is arbitrary because "the bond between the signifier and the signified is arbitrary." The idea of "sister" is not linked to the sound of the word "sister." The link between the idea and the sound--or the signified and the signifier--is a matter of societal convention.

2) The linear nature of the signifier--The signifier is of a linear nature because "auditory signifiers have at their command only the dimension of time." It "represents a span, and the span is measurable in a single dimension"--that of time.
 

        Saussure rejects a theory of language as "a naming-process only--a list of words, each corresponding to the thing that it names." He does so because such a theory "assumes that ready-made ideas exist before words; it does not tell us whether a name is vocal or psychological in nature . . . finally it lets us assume that the linking of a name and a thing is a very simple operation." Saussure says that "the linguistic unit is a double entity, one formed by the associating of two terms." Instead of uniting a thing with a name, the linguistic sign untes a concept with a sound-image. Saussure defines the sound-image, not as the physical sound but as the psychological imprint of the sound upon our senses.
        The word "concept" is replace by the word "signified," while the word "sound-image" is replaced by the word "signifier." The signified and the signifier together make up the sign.
        Saussure has two basic, and famous, principles: 1) The arbitrary nature of the sign; and 2) The linear nature of the signifier. The sign is arbitrary because "the bond between the signifier and the signified is arbitrary." The idea of "sister" is not linked to the sound of the word "sister." The link between the idea and the sound--or the signified and the signifier--is a matter of societal convention. The German word Schwester and the Spanish word hermana each refer to the idea of "sister," but the sounds of the respective signifiers are nothing alike. The signifier is of a linear nature because "auditory signifiers have at their command only the dimension of time." It "represents a span, and the span is measurable in a single dimension"--that of time. 
        Saussure also distinguishes between what he calls langue--the system of a language, the language as a system of forms--and parole--actual speech, the speech acts that are made possible by the language.