Ferdinand de Saussure represented meaning in terms of the above diagram. It depicts how an abstract mental concept is expressed in material form through a "sound-image" (i.e., an utterance, a written word, a picture). The two elements are irreducibly united, each evoking the recollection of the other. The mental concept is called the signified, and the material sound-image is better known as the signifier. Meaning, then, is instantiated in the process of signification. Roland Barthes, Mikhail Bahktin, and Jacques Derrida all impose modifications on this basic diagram to fit their own theories. This model will be used as a basis in more clearly illustrating their special contributions.

--Image copied from Course in General Linguistics