These terms name functions or roles played by syntactic units inside a clause. The units which can play these roles may be clauses as well as non-clause constituents.
Subject - a topic of discussion, about which the predicate makes a comment. May be a nounn phrase or a subordinate clause (or other type of unit in certain sentence types). Except when the subject position introduces a topic, the subject is usually given information, that is, information that is already known to all the particpants in the communication.
Predicate - makes a comment about the subject. Will always include a verb, although the verb may or may not carry a present- or past-tense marker (see finite/nonfinite, below). The predicate may contain additional elements that modify the verb or subject: NPs, PPs, APs, AdvPs, or subordinate clauses. New information is usually contained in the predicate, especially in the last position. Most predicates contain some given and some new information (new information is information that only the speaker knows, and wishes to communicate to the other people involved in the communication event.)
Sentence-level adverbial -This is an adverbial that makes a comment on the whole sentence, not just a part of it. It is often an evaluative comment. One characteristic of sentence-level adverbials is that they can move around. They may be placed at the beginning, middle, or end of a sentence. In the following examples, the sentence adverbial is in italics.
Unfortunately,
your mother's condition has worsened.
sentence adverbial
sentence
Your mother's condition, unfortunately, has worsened. Your mother's condition has unfortunately worsened. Your mother's condition has worsened, unfortunately.
Obviously,
your friend doesn't really want to come to your party.
sentence adverbial
sentence
Your friend obviously doesn't really want to come to your party. Your friend doesn't really want to come to your party, obviously.
Sentences with sentence-level adverbials can often be paraphrased with the adjective version of the adverb, thus:
It is unfortunate that your mother's condition has worsened. It is obvious that your friend doesn't really want to come to your party.
Or thus:
That your mother's condition has worsened is unfortunate. That your friend doesn't really want to come to your party is obvious.
Sentences with adverbials within the predicate cannot be paraphrased in these ways:
He carefully inserted the key into the lock. 'Carefully' is in the predicate, modifying the verb, not the whole sentence. (* means that a native speaker would reject the sentence.)
* It was careful that he inserted the key into the lock. * That he inserted the key into the lock was careful.
Predicate Roles
A sentence describes an event, a scene, or a situation. These scenarios may involve people, objects, times, places, reasons, etc., etc. Linguists often refer to the people and objects in a scenario as participants, even if they aren't doing anything in particular.
Constituent roles express aspects of a scenario; they are very much based on the real relations and events the speaker is talking about.
When we create an utterance to express information about a scenario, we make many choices: What words will we use? What sentence patterns will we choose? How will we assign participants in the scenario to constituent roles? How do we do all this in a way that helps our listeners or readers follow our meaning easily? We make these choices incredibly rapidly, and, again, usually not thinking about it. Most speakers of most languages could not explain the choices they make if their lives depended on it; it takes extensive training in grammar, semantics, and discourse to do so.
Usually, a great deal of information the speaker wants to express resides in the predicate. A number of roles are found there.
Direct object - this is present in a clause that portrays an action or event with two or more participants, in which at least two participants are named. The direct object is the person or thing that the action of the verb is directed towards. A direct object may be a NP or a subordinate clause. The direct object can be thought of as an undergoer of the verb's action in many cases.
(names participant #2: undergoer of seeing [the UFO was seen])
subject
direct object
Indirect object - this is present in a sentence that portrays a three-way action or event: there are at least three participants. The indirect object is the expression that names the participant who benefits from the action, or who receives the direct object, or who is indirectly affected by the verb's action. An indirect object may be a NP or a subordinate clause. Thinking of the events in order may help sort out direct from indirect object: First, the agent found the job; then, I got the job. First, Susan sent the birthday card, then, her girlfriend received it. This is helpful especially because the sentence order has the indirect object first.
My agent
found
me
a job.
NP
V
NP
NP
names participant #1: did the finding
action
names participant #3: benefitted from the action (got the job)
names participant #2: is the thing that was found
subject
verb
INDIRECT OBJECT
direct object
The Mustangs
gave
the Grizzlies
a serious beating.
NP
V
NP
NP
names participant #1: did the giving
action
names participant #3: got the beating
names participant #2: what was given
subject
verb
INDIRECT OBJECT
direct object
Susan
sent
her girlfriend
a birthday card.
NP
V
NP
NP
names participant #1: did the sending
action
action names participant #3: got the card
names participant #2: was sent
subject
verb
INDIRECT OBJECT
direct object
My husband
made
the baby
some mashed carrots.
NP
V
NP
NP
names participant #1: did the making
action
names participant #3: got the carrots
names participant #2: were made
subject
verb
INDIRECT OBJECT
direct object
There is a failsafe test for indirect objects: if you can express the same role with a PP using 'to' or 'for' placed after the direct object, you have an indirect object. I call this the 'to-for test'. Examples:
My agent found a job for me. The Mustangs gave a serious beating to the Grizzlies. Susan sent a letter to her girlfriend. My husband made some mashed carrots for the baby.
Subject complement -this is an expression that occurs after the verb, but describes the subject of the sentence. The meaning of the subject complement is tied to the subject. In traditional grammar, these are called predicate nominatives when they are NPs and predicate adjectives when they are APs.
My father
was
a dentist.
NP
V
NP
subject
describes my father subject complement (predicate nominative)
The horses
are
very beautiful.
NP
V
AP
subject
describes the horses subject complement (predicate adjective)
Object complement - This also occurs after the verb, but it describes the direct object. (Sentences with subject complements do not have direct objects.)
We
consider
her
the best candidate for the job.
NP
V
NP
NP
subject
direct object
describes 'her' (object complement)
I
found
the new guy
very handsome
NP
V
NP
AP
subject
direct object
describes 'the new guy' (object complement)
Adverbial - Provides descriptive information about the verb's action. Phrases or clauses can be adverbials; the phrases can be PPs (not all adverbials are adverbs!!) or AdvPs. Adverbials answer questions like when, why, in what manner, in what way or fashion, how, where. It is not uncommon to have several adverbials in a sentence, giving various types of information.