1. Becker, M., 2000. The development of the copula in child English: the lightness of be. PhD Thesis, UCLA.
2. English has two copulas;Becker,2002
3. Language Development: Form and Function in Emerging Grammars;Bloom,1970
4. A First Language;Brown,1973
5. Clausal structure and the Modern Irish copula;Doherty;Natural Language and Linguistic Theory,1996