I'm trying to think things through regarding case and passive verbs, within the framework of Government and Binding Theory.
As starting point, I'll use this statement/principle (based on what I've read): passive verbs do not assign case.
Active verbs assign case (i.e. They ate the cookies, where "the cookies" gets accusative case from the active verb). In passive, I can't say "were eaten the cookies" because passive verbs don't assign case. What happens then (unless I'm mistaken) is that "the cookies" moves out of that position and is promoted to subject (i.e. to the left of "were eaten") where "The cookies" gets nominative case by INFL. This leftward movement satisfies the basic principle that all finite verbs require subjects: The cookies were eaten.
Now, from the active They gave her cookies (where "cookies" gets accusative case), we get the passive She was given cookies (by them). In the passive version, "her" is promoted to subject, and "cookies" remains in place, which means that passive "given" assigns accusative case (right?). This, however, violates my original statement/principle that "passive verbs do not assign case."
Is the statement/principle "passive verbs do not assign case" actually viable in English? Or does it need to be revised? If so, how? Saying something like "passive verbs don't assign case, unless they assign case" doesn't seem productive/rigorous (it's like saying "x doesn't do y, unless x does y).
Is the very notion of "case" not really applicable to English (English being morphologically weak)? Accordingly, we don't need to bother with terms such as "accusative" and "nominative" (though I see that such terms are commonly used).
In any event, I wonder how linguists approach such issue.
Thanks in advance.