Systemic organisation of the language. Variability and variation. Language norm in general. Norm modifications: causes and conditions. the problem of norm codification (views of Jan Niecisław Ignacy Baudouin de Courtenay, Aleksey Shakhmatov, Alexander Peshkovsky and contemporary linguists). How codification influences the norm. The influence exerted on the norm by psycholinguistic and sociolinguistic factors: social dependence of linguistic phenomena, prestige value of certain forms used in speech. Double forms.