F. de Saussure defined language structurally as a system of signs used for communication. The signs are arbitrary (made up) and language is a social phenomenon. Language has two basic functions: communication and identity. We will deal with the communicative and linguistic aspects in other chapters. Here we will consider the identity function.
The main requirement of a group is to find a way to distinguish members from non-members. Group members learn a language within the group and only those who belong to the group can use it to a high degree of competence. Therefore language is the principal factor through which people can distinguish whether a stranger belongs to their group or not, and in most cases also to which other group that person belongs.
Languages such as Esperanto, pidgins and creoles are normal human languages in the same way as are ethnic languages, dialects and other forms of speech. The basic requirement for any linguistic system to be a human language is that it be in regular use by a community.
Human beings created writing, and then states, and the states established state languages which differ from other spontaneous languages by being standardized. Standard languages are regulated by spelling and pronunciation models, grammar and dictionaries, and they are written. Therefore, changes in such languages are slower than in spontaneous language.
Each person belongs simultaneously to many groups (family, city, region, nation, religion, philosophy, groups of friends, etc.). And each group tends to develop variations of language which demarcate it from other groups. Therefore, each speaker in practice speaks many language varieties, or registers, even if not aware of this. Humans are multilingual by nature.
Each language also tends towards more extensive use than within its own group and each tends towards some use by neighboring groups to facilitate communication. In this sense, some languages continue to grow due to the general strength of their speakers (economic, military, etc.), and the strength and attractiveness of their cultures (cultural products include art, education, religion, entertainment industries ...) and become international languages which are more or less widely used.
