A sentence is the basic unit of written English language communication. We grant poets, playwrights, and fiction writers some "literary license." These authors can experiment with the language or use the language in an unconventional manner. Expository writing is conveyance of information, often necessary or even vital information, to readers who need that information. If a reader misinterprets a sentence in a work of fiction, no harm results. A misinterpretation of nonfiction writing can cause harm. Written instructions, policies, procedures, guidelines, research reports, personal communication, and news media information need to be written so that the reader understands exactly what the writer intended.

IMAGINE. Tomorrow will be a short school day. The school day will terminate at 11 am. The school administrators deliver a carelessly prepared message to the school bus drivers telling them to be at the school at 1 pm.

simple sentence

The basic English language sentence is called a simple sentence. It requires a subject and a verb. We ordinarily include some additonal words that explain the subject. The sentence or a part of a sentence that contains a subject and a verb and constitutes a complete thought is called an independent clause.

I like English.

The sentence above conveys a complete thought. The subject is I, and the verb is like. The word English conveys an understanding of what the subject likes. The sentence has one independent clause and is a simple sentence. Observe the arrangement or sequence of sentence components: subject, verb, other parts of the sentence. This arrangement is not mandatory, but sentences written in this format are usually easy to understand.

complex sentence

A complex sentence contains an independent clause and a subordinate clause. The independent clause can function as a complete sentence. The subordinate clause also contains a subject and a verb but cannot function as an independent sentence.

We surveyed the damage as the wind subsided.

We surveyed the damage. This is an independent clause and a complete sentence. The words convey a complete thought. The words as the wind subsided form a subordinate clause. The words do not convey an intelligent thought that can stand alone as a sentence. If we modify as the wind subsided so that it becomes The wind subsided, we realize that it contains both a subject and a verb. The words as the wind subsided constitute an adverbial expression that describes a condition that existed when we surveyed the damage.

compound sentence

A compound sentence contains two independent clauses. Two independent clauses may be joined by a comma and a conjunction, or by a semicolon, or by a colon.

The school year ends June 1st, but the sports program will continue throughout the summer.

We accept the design; it meets our standards.

The school board funded the computer laboratory; consequently, computer classes will be offered next year.

The judge has decided the case, and he ruled as follows:  "The court finds the defendant guilty and sentences him to time served."

You can write as many independent clauses and subordinate clauses into a single sentence as your imagination will support. However, reader comprehension declines as complexity increases.

Sentences may be classified according to the purpose of the sentence.

sentence classification by purpose

A declarative sentence is used to make a statement.
An interrogative sentence is used to pose a question.
An imperative sentence is used to give a command or to implore or entreat.
An exclamatory sentence is used to express astonishment or extreme emotion.

Most of the sentences we speak or write are declarative sentences.

declarative sentences

It's lunch time.
We are going to the game on Friday.
My car is out of gasoline.
My parents keep telling me that I should make good grades so I can get a job or go to college.

We frequently ask questions, perhaps not as frequently as we should.

interrogative sentences

What time does the movie start?
How many people from your graduating class went to college?
Is there a reason why these dirty clothes are in the middle of the floor?
What are they serving in the cafeteria today?

People who have authority use imperative sentences. Sometimes, people who don't have authority use imperative sentences. The results may differ.

imperative sentences

Wash the car.
Clean up your room.
Martin, report to the counselor.
Please donate to the community charity fund.

We say that sentences must have a subject and a verb. Note that some of the above sentences do not seem to have a subject. The subject is implied, and the implied subject is you. You wash the car. You clean up your room. You is a second person pronoun. It isn't possible to make a command statement in first person or third person.

Exclamatory sentences are rarely used in expository writing. Spoken exclamations are often a single word or an incomplete sentence. Grammarians indicate that formal exclamatory sentences begin with the word what or with the word how. Most of the exclamations we encounter are informal.

exclamatory sentences

What a beautiful night!
How happy we were when the dawn came and our flag was still there!
What did you do to your hair! (exclamation formed as a question)
I just won 500 dollars! (exclamation formed as a declarative sentence)

How do you know if a sentence is a question? Well, according to commedians Bud Abbot and Lou Costello, it depends on the punctuation mark.
"Who's on first."