Saussure, Ferdinand. "Signs and Language." From Alexander, Jeffrey C., and Steven Seidman. Culture and Society: Contemporary Debates. Cambridge [England]: Cambridge University Press, 1990.
Originally published 1916. (Saussure died 1913)
The basics of semiotics:
Signs consist of signified (concept) and signifier (sound-image).
Signs are arbitrary. More specifically the relationship between the signified and the signifier (an essentially random collection of syllables/letters) is arbitrary.
The signifier is linear. A word only functions as a sign if you read it/say it in the linear way it is meant to be said.
The sign is immutable. No one can consciously create a sign. Language is handed down from the past.
The sign is mutable. Time change the sign as long as it perpetuates.
Thus, the principle of general semiology: "continuity in time is coupled to change in time."