1. Aarts, Bas. 2007. Syntactic Gradience: The Nature of Grammatical Indeterminacy. Oxford: Oxford University Press.
2. A lovely little example
3. Aijmer, Karin. 1997. “I think: An English Modal Particle.” In Modality in Germanic Languages: Historical and Comparative Perspectives, edited by TorilSwan and OlafJansen Westvik, 1–47. Berlin: Mouton de Gruyter.
4. Bolinger, Dwight. 1980. “Wannaand the Gradience of Auxiliaries.” In Wege zur Universalienforschung: Sprachwissenschaftliche Beiträge zum 60. Geburtstag von Hansjakob Seiler[Ways into research on universals: Linguistic contributions to Hansjakob Seiler's 60th birthday], edited by GunterBrettschneider and ChristianLehmann, 292–299. Tübingen: Narr.
5. Boye, Kasper. 2010. “Raising Verbs and Auxiliaries in a Functional Theory of Grammatical Status.” In Language Usage and Language Structure, edited by KasperBoye and ElisabethEngberg-Pedersen, 73–104. Berlin: De Gruyter Mouton.