Core Arguments

A noun or pronoun acting as the subject of a verb. Its head is the verb. It is usually the easiest relation to find in a tree: find the root first, then ask who or what is doing the action.

How the parser decides: the noun or pronoun that agrees with the verb. In a statement it comes before the verb. The label goes on the noun, never on the determiner in front of it.

A sentence can carry several. An embedded clause has a subject of its own, and it is also nsubj, but its head is the embedded verb, not the root.

The subject of a passive verb — grammatically the subject, but semantically the thing the action happened to. The bridge did not rebuild anything.

How the parser decides: the subject of a verb that also has an auxpass child. The two labels come as a pair: if you find one, look for the other on the same verb.

A whole clause serving as the subject. The label goes on the verb of that inner clause, which is what makes it look strange at first — the arc runs verb-to-verb.

How the parser decides: the root has no nominal subject of its own, and a subordinate verb occupies the slot where one would be. Rare in ordinary prose.

The direct object: the thing the verb acts on. Its head is the verb, and unlike a subject it normally follows.

How the parser decides: a noun or pronoun after the verb, with no preposition in front of it, that is not the indirect object. When the verb has two objects, as in brought us coffee, the second one is the dobj.

The indirect object: the person or thing that receives something. It gets this label when it comes right after the verb, before the direct object, with no preposition in front of it.

How the parser decides: mostly by position. In gave Nora the keys, two nouns follow the verb, and the first one, Nora, is the dative.

A noun after a linking verb that renames the subject — the traditional predicate nominative. The winner and a stranger are the same person.

How the parser decides: a noun complement of a linking verb. The linking verb (here was) is the root, and the complement hangs from it. The parser never uses the separate cop label.

An adjective after a linking verb, describing the subject. It fills the same slot as attr; the difference is the part of speech of the complement.

How the parser decides: an adjectival complement of a verb. Comparatives behave identically to plain adjectives here.

An object predicate: a word describing the direct object rather than the subject. In elected him treasurer, treasurer is what him became.

How the parser decides: the label covers two different constructions. In one, the word follows a direct object and renames or describes it (elected him treasurer). In the other, there is no object at all: the word usually follows seem or appear and describes the subject (seems conclusive).

A clausal complement with its own subject — a whole clause functioning as the object of a verb, often a verb of saying, thinking or asking.

How the parser decides: the complement clause has a subject that is not shared with the outer verb. This is the one distinction that separates it from xcomp.

An open clausal complement — one whose subject is missing and understood to be the outer clause’s. In Ravi wants to learn, the learner is Ravi, but nothing in the inner clause says so.

How the parser decides: a complement clause with no subject of its own. “Open” means exactly that gap.

So a to-infinitive is not always an xcomp. In Omar wants his sister to drive, sister is the nsubj of drive. The infinitive has its own subject, so drive is a ccomp. Spanish speakers often write Omar wants that his sister drives ✗, from quiere que su hermana maneje. That is not correct English: after want, English uses the person and then a to-infinitive.

The object of a preposition. Its head is always the preposition itself, never the verb or noun that the whole phrase modifies. That is why a prepositional phrase takes two arcs, not one.

The label sits on one word, the head noun: sofa, not the sofa. The phrase that word heads — it plus everything hanging below it — is what the Roles exercise boxes as the object of the preposition. The same holds for every relation on this page: nsubj marks keys, and the subject is The keys.

How the parser decides: the noun or pronoun that a prep introduces. It is one of the most common relations, and it always hangs from its preposition.

What a preposition takes when its object is a verb form rather than a noun. Most often this is an -ing form, a gerund. It can also be the verb of a clause: in thought about what he said, said is the pcomp of about.

How the parser decides: the complement of a preposition is verbal. Compare insisted on the delay (pobj) with insisted on leaving (pcomp).

The word by in a passive sentence. It usually introduces the doer, the person or thing that performed the action. It is a preposition with a label of its own: agent sits on by itself, and the noun below it is an ordinary pobj.

How the parser decides: by attached to a passive verb, even when it does not name a doer. In The car was parked by the door, by names a place, but the verb is passive, so by is still the agent. After an active verb, a by that names a place is a plain prep: she waited by the door.