What are the possible theta roles for to-infinitives in these sentences? [migrated]

Solution 1:

Theta roles only apply to noun phrases, not to all verbal arguments. The phrase to sleep is not a noun phrase, so it doesn't have a theta role. (In some theoretical frameworks, that clause contains a "null subject" called PRO, which can be assigned a theta role; its theta role would then be the same as that of her in the next sentence.)

In your second sentence I want her to sleep, the theta role of her would probably be described as Experiencer, since she is the one "experiencing" sleep. That said, linguists who work in a theta-role framework don't all use the same list of theta roles, and there can be disagreements about how best to classify specific instances.

Your third example, I want to sleep her, is not a grammatical English sentence, so it can't really be analyzed.