1. Need, auxiliary;Bolinger;College English,1942
2. A new approach to English grammar, on semantic principles;Dixon,1991
3. The use of the verb dare in blends between the modal and main verb constractions;Duffley;Canadian Journal of Linguistics,1992
4. The English infinitive;Duffley,1992
5. The meanings of the modals in present-day American English;Ehrman,1966