1) The structure of language depends on the complementarity between combination into a syntagm (V+DP) and selection of a lexical paradigm: eat + DPZ [V eat] + [DP an apple] // [V eat] + [DP many cakes].
2) The selection of one unit rather than another from a paradigmatic set is relevant informationally: eat apples/plums/cherries
3) It is often the case that one language will pack into a single lexical item (i.e., paradigmatically) information which is conveyed by means of a syntagm in a different language:
English: toe/finger Polish: palec nogi/ palec ręki
4) In the study of lexical relations we will distinguish between paradigmatic and syntagmatic relations.
d) The language/ speech opposition From the point of view of lexical semantics a relevant problem is that between meaning registered in the lexicon (language) and meaning in context (speech)
De Saussure argues that the sign is arbitrary by naturę.
By arbitrariness he means that the sign is not motivated, that it is arbitrary with respect to the signified (content), with which it has no natural relation. That is, there is an arbitrary relation between the sign and the referent; e.g., the sign boeuf has no relationship to the animal it designates in French; in English, the same animal is designated by the sign ox.
On the other hand, the relationship between the signifier (sound) and the signified (content) is a necessary relation.
The relations sign/referent, and implicitly signifier/signified, hołd by convention.
A convention is a regularity of thought and behavior known by the members of a community and which is observed only because everybody else observes it, sińce in itself, it is not motivated by any other reason.
The signifier/signified relation cannot be questioned or challenged, hence the immutability ofthe sign at any given synchronic moment.
At the same time, he sign is historically mutable. There are frequent changes of meaning and form; that this is possible is also the consequence of the arbitrary naturę of the sign.