Basically, a sentence is a combination of two grammatical units—the subject and the predicate.

Subject

The subject of a sentence refers to what the sentence is about, often the person or thing that carries out the action of the verb. The subject usually gives a clear idea of what the sentence is about.

The subject can be a noun—either a common noun or a proper noun or a verbal noun; a noun phrase; a pronoun; a subordinate clause; an infinitive.

In the following sentences the bolded words form the subject of the sentence and the subjects are nouns:

Accommodation is expensive in that area.
People are beginning to leave.
Jane is giving a party.
Jim has resigned.

In the following sentences the bolded words form the subject of the sentence and the subjects are noun phrases:

The large black dog bounded up to the child.
Those terrible floods affected many people.
James, my brother-in-law and dear friend, has just died.

In the following sentences the bolded words form the subject of the sentence and the subjects are pronouns:

You have passed the exam.
He denied the charge.
She lost her wedding ring.

In the following sentences the bolded words form the subject of the sentence and the subjects are subordinate clauses:

Who she was remained a mystery.
Why he left has not yet been revealed.
What he says is not true.

In the following sentences the bolded words form the subject of the sentence and the subjects are infinitives:

To get there is going to be very difficult.
To marry young is her main aim.
To get through your exams should be your principal concern.

Dummy Subject

A dummy subject sometimes has no intrinsic meaning but is inserted to maintain a balanced grammatical structure. In the sentences

It has started to rain. and
It is nearly midnight.

the word It is a dummy subject.

In the sentences

There is nothing else to say. and
There is no reason for his behavior.

the word There is a dummy subject.

In sentences which are directives the subject often does not appear, but is implied, as in:

Get this out of here. and
Lend me that pen for a minute, please.

The implied subject is you.

Subject and Predicate Examples

Predicate

The predicate refers to the part of a sentence or clause that gives information about the subject. It is basically all the parts of a clause or sentence that are not contained in the subject. It can either be a single verb or a number of elements. Thus in the sentence

The little girl fell.

the word fell is the predicate of the sentence.

Similarly, in the sentence

The tired old man slept soundly.

the words slept soundly form the predicate of the sentence.

And in the sentence

The tired old man slept like a log.

The words slept like a log form the predicate of the sentence.

In the following sentences the bolded words form the predicate of the sentence:

Jane fainted.
Peter was rich and powerful.
Children screamed loudly.
The lights went out all of a sudden.
Workers protested long and loudly at the factory gates.

Object

Very often the predicate contains an object. The object of a sentence is the part of a sentence that is acted upon or is affected by the verb. It usually follows the verb to which it relates.

There are two possible forms of object in a sentence or clause—a direct object or an indirect object.

Direct Object

A direct object refers to the person or thing that is directly affected by the action described by the verb. The direct object can be a noun, and in the sentence

The girl hit the ball.

the word ball is a noun and the direct object.

A direct object can also be a pronoun, and in the sentence

She hit him.

the word him is a pronoun and the direct object.

A direct object can also be a noun phrase, and in the sentence

He has bought a large Victorian house.

the phrase a large Victorian house is a noun phrase and the direct object.

A direct object can be a noun clause, and in the sentence

I know what he means.

the clause what he means is a noun clause and the direct object.

In the following sentences the bolded words form a direct object:

The dog bit the child.
He dislikes cats.
We loved them.
People admire her.
He wanted a comfortable city-centre flat.
She lost her diamond engagement ring.
I don’t know what you mean.
I asked why you did that.

Indirect Object

An indirect object usually refers to the person who benefits from the action described by the verb, often by receiving something. In the sentence

Her father sent the school a letter.

the school is the indirect object and a letter is the direct object.

If there is a direct object and an indirect object in a sentence or clause, the indirect object is almost always placed before the direct object, as in:

I gave the boy the sweets.

where the boy is the indirect object and the sweets the direct object.

However, if both the direct and indirect objects are pronouns the direct object is sometimes placed first, especially in informal speech, as in:

That is my book.
Give it to me, please.

Verbs and Indirect Objects

Some verbs commonly take an indirect object as well as a direct object. These include bring, buy, give, send, show, tell. In the following sentences the bolded words form an indirect object.

I sent you the book.
She showed her mother the letter.
We had to tell her the bad news.
They gave the children some sweets.
Mary bought them some magazines for the journey.
Pass me the salt, please.

An indirect object can be preceded by the word to or for. So the sentence

Her father sent the school a letter.

could be rephrased as

Her father sent a letter to the school.

And in this case the direct object would come before the indirect object.

Complement

In a sentence where the verb is a linking verb, such as be, become, seem, etc, what follows the verb in a predicate is called not an object, but a complement.

In the sentence

Mark is a policeman.

the words a policeman form the complement of the sentence.