De Saussure argued for a distinction between langue (an idealized abstraction of language) and parole (language as actually used in daily life). He argued that the "sign" was composed of both a signified, an abstract concept or idea, and a "signifier", the perceived sound/visual image.
Because different languages have different words to describe the same objects or concepts, there is no intrinsic reason why a specific sign is used to express a given signifier. It is thus "arbitrary".
Signs thus gain their meaning from their relationships and contrasts with other signs. As he wrote, "in language, there are only differences 'without positive terms.'"[4]