Abstract
Complementarity is a principle and a sine qua non condition in code switching or in the bilingual communication process and is governed by its conditions, factors and components. The classic definition of code switching is the perfect switching of languages within the same communicative act. Bilinguals who have language skills in both languages often change code, those who speak one language much better than another, change less frequently. Such switching requires a high command of both languages as well as a complementarity between them. Something completely opposite to borrowing of words, where you really don’t have to master the language from where the word is taken.