Complements, Objects and Grammatical Functions

Words and phrases perform different grammatical functions within a sentence. Understanding these functions is more useful than simply labeling words according to their parts of speech.

Subject

The subject is generally the main participant or topic of a clause and controls agreement in many constructions:

The student passed the examination.

Object

An object is commonly associated with the action or meaning of a transitive verb.

A direct object:

She opened the window.

An indirect object:

She gave the student a book.

The indirect object commonly represents a recipient or beneficiary.

Subject Complement

A subject complement follows a linking verb and describes or identifies the subject:

She is a doctor.
He became angry.

The complement is related directly to the subject rather than being an object of the verb.

Object Complement

An object complement describes or identifies the object:

They elected him president.
The news made her happy.

Here president describes him, while happy describes her.

Predicative Complements

A predicative complement is a complement that characterizes or identifies another element, typically following a linking verb or certain complex-transitive verbs.

The sky became dark.
She seems tired.

Recognizing predicative complements helps distinguish sentences such as:

She became a doctor.

from:

She visited a doctor.

In the first sentence, a doctor is a complement; in the second, a doctor is an object.

Adverbials

Adverbials provide information about circumstances such as time, place, manner, reason, frequency, or condition:

He arrived yesterday.
She works in Islamabad.
They spoke very quietly.

Unlike objects and complements, adverbials are often optional:

She works.
She works in Islamabad.

Grammatical Function vs Part of Speech

The same part of speech can perform different functions:

Ali arrived. — noun functioning as subject
I saw Ali. — noun functioning as object

Likewise, a phrase can function as a subject:

The new English teacher arrived.

Therefore, part of speech tells us what something is, while grammatical function tells us what it does in the sentence.