References
Charles A. Ferguson
(1978). Historical background of universals research. In J. Greenberg (Ed.). Universals of human language (pp. 7-32). Stanford: Stanford University Press.
with Greenberg, J. , Moravcsik, E.A. (eds) (1978). Universals of human language 4: syntax. Stanford: Stanford University Press.
(1959). Diglossia. Word, 15, 325-340.