Case

There are two features responsible for case-assignment:
case, possible values: nom, acc, gen, none
assign-case, possible values: nom, acc, none Case assigners (prepositions and verbs) as well as the VP, S and PP nodes that dominate them have an assign-case case feature. Phrases and lexical items that have case i.e. Ns and NPs have a case feature. Case assignment by prepositions involves the following equations:

(565)0(565

(566)

PP.b:assign-case P.t:case 

(566)0(566

(567)

NP.t:case P.t:case 

Prepositions come specified from the lexicon with their assign-case feature.

(567)0(567

(568)

P.b:assign-case acc 

Case assignment by verbs has two parts: assignment of case to the object(s) and assignment of case to the subject. Assignment of case to the object is simpler. English verbs always assign accusative case to their NP objects (direct or indirect). Hence this is built into the tree and not put into the lexical entry of each individual verb.

(568)0(568

(569)

NP_object.t:case acc 

Assignment of case to the subject involves the following two equations.

(569)0(569

(570)

NP_subj:case VP.t:assign-case 

(570)0(570

(571)

VP.b:assign-case V.t:assign-case 

This is a two step process - the final case assigned to the subject depends upon the assign-case feature of the verb as well as whether an auxiliary verb adjoins in. Finite verbs like sings have nom as the value of their assign-case feature. Non-finite verbs have none as the value of their assign-case feature. So if no auxiliary adjoins in, the only subject they can have is PRO which is the only NP with none as the value its case feature.