Language is a varied living reality, which is defined by the linguistic usages of the speakers in their social context. Variation can be due to the speakers geographical dispersion, but also to their position in the structure of society (stratification). The latter form of variation, which intersects the former one, will be here taken into consideration. We will start from the premise that, beyond the abstract linguistic competence, established by theoretical grammar and based on the work of Saussure and, later, Chomsky (which has led to the acknowledgement of a naïve "linguistic communism") there is a social competence. The social competence is unequally spread and is bound to the different microcosms of a stratified human community, all governed by rules which determine the form of the existing discourses at work in society. These rules can be explicit or implicit and more or less coercive. Their learning is an essential component of our construction as speakers / social actors. 1. Language as a cultural practice. Cultural and linguistic diversity. 2. Linguistic communities? 3. Linguistic competence / Social competence. 4. Social stratification and language. 5. Linguistic discourses and social construction.