The concept of the arbitrariness of the sign is foundational in Saussurian linguistics. In the first part of the essay Saussure writes "The bond between the signifier and the signified is arbitrary. Since I mean by the sign the whole that results from the associating of the signifier with the signified, I can simply say: the linguistic sign is arbitrary". Although the signifier is treated by its users as 'standing for' the signified, Saussurean semioticians emphasize that there is no necessary, intrinsic, direct or inevitable relationship between the signifier and the signified. Saussure stressed the arbitrariness of the sign - more specifically the arbitrariness of the link between the signifier and the signified. He was focusing on linguistic signs, seeing language as the most important sign system; for Saussure, the arbitrary nature of the sign was the first principle of language. In the context of natural language, Saussure stressed that there is no inherent, essential, 'transparent', self-evident or 'natural' connection between the signifier and the signified'-between the sound or shape of a word and the concept to which it refers. Not that Saussure himself avoids directly relating the principle of arbitrariness to the relationship between language and an external world, but that subsequent commentators often do, and indeed, lurking behind the purely conceptual 'signified' one can often detect Saussure's allusion to real-world referents.
In language at least, the form of the signifier is not determined by what it signifies: there is nothing 'treeish' about the word 'tree'. Language differ, of course, in how they refer to the same referent. No specific signifier is 'naturally' more suited to a signified than any other signifier; in principle any signifier could represent any signified. Saussure observed that 'there is nothing at all to prevent the association of any idea whatsoever with any sequence of sounds whatsoever', 'the process which selects one particular sound-sequence to correspond to one particular idea is completely arbitrary'.
