A sentence is a group of words giving a complete thought. A sentence must contain a subject and a verb (although one may be implied).

Examples of Sentences

There are four types of sentence. (A sentence can convey a statement, a question, an exclamation or a command.)

(1) A Declarative Sentence. A declarative sentence conveys a statement and ends with a full stop.
  • I have a dog.
  • He has every attribute of a dog except loyalty. (US politician Thomas Gore)
(2) An Imperative Sentence. An imperative sentence is a command or a polite request. It ends with an exclamation mark or full stop.
  • Buy me a dog.
  • When a dog runs at you, whistle for him. (Philosopher Henry Thoreau)
(3) An Interrogative Sentence. An interrogative sentence asks a question and ends with a question mark.
  • Does your dog bite?
  • Who knew that dog saliva can mend a broken heart? (Author Jennifer Neal)
(4) An Exclamatory Sentence. An exclamatory sentence expresses excitement or emotion and ends with an exclamation mark.
  • You bought me a dog!
  • In Washington, it's dog eat dog, but, in academia, it's exactly the opposite! (US politician Robert Reich)
In an imperative sentence (an order) or an interrogative sentence (a question), the subject or verb is often implied.
  • Run!
  • Go.
  • (This is the shortest sentence in English.)
  • Why?
The shortest sentence without an implied subject or verb is "I am" or "I go".

More about Sentences

A sentence consists of a main clause and sometimes one or more subordinate clauses. A sentence must contain at least one independent clause. (An independent clause is one that can stand alone as a sentence. In the examples below, the independent clauses are underlined.) There are four sentence structures.

(1) A Simple Sentence. A simple sentence has one independent clause and no subordinate clauses.
  • I have a dog.
  • You can't surprise a man with a dog. (Screenwriter Cindy Chupack)
(2) A Complex Sentence. A complex sentence has an independent clause and at least one dependent clause.
  • When I was a young boy, we had a huge dog.
  • Diplomacy is the art of saying "nice doggie" until you can find a rock. (Actor Will Rogers)
(3) A Compound Sentence. A compound sentence has at least two independent clauses.
  • I want a dog, but we've got a cat.
  • Cry "Havoc ", and let slip the dogs of war. (William Shakespeare)
(4) A Compound-Complex Sentence. A compound-complex sentence has at least two independent clauses and at least one dependent clause.
  • When I move house, I'll buy a dog, and I'll buy a cat.
  • When a dog bites a man, that is not news because it happens so often, but if a man bites a dog, that is news. (Editor John Bogart)

Why Should I Care about Sentences?

There are four great reasons to understand sentence structures and the types of the sentence.

(Reason 1) Avoid the run-on sentence.

By far the most common mistake made by people with otherwise sound writing skills is the run-on sentence. Typically, this error is caused by writing a sentence, putting a comma, and then writing another sentence.
  • I love the mountains, they remind me of home. [wrong]
  • Love is so short, forgetting is so long. [wrong] (Chilean politician Pablo Neruda)
You cannot end a sentence with a comma. These should both be two sentences (or rewritten to punctuate them correctly). Remember, a sentence contains a subject and a verb and gives a complete thought. The criteria for what constitutes a sentence are satisfied twice in each example.

The run-on sentence usually occurs because writers feel a full stop is too much of speed bump between their closely related sentences. The jolt of a full stop can be smoothed with other punctuation (but not a comma).
  • Don't play hide and seek; no one would look for you.
  • (You can smooth the jolt of a full stop by merging your two sentences into one with a semicolon.)
  • I like a woman with a head on her shoulders – I hate necks. (Actor Steve Martin)
  • (You can smooth the jolt of a full stop by merging your two sentences into one with a dash. A dash looks quite stark, and it looks a little informal.)
  • My friend is a procrastinator…he's afraid of Saturday the 14th.
  • (You can smooth the jolt of a full stop by merging your two sentences into one with three dots (or ellipses). Using three dots creates a pause for effect, and it looks informal.)
This is covered more in the entries on run-on sentences, full stops, dashes, semicolons and ellipses (three dots).

(Reason 2) Punctuate your sentences correctly.

Understanding the four sentence structures assists with deciding how to punctuate sentences. More specifically, it assists with the following two common decisions:

(1) Deciding whether to use a comma with the subordinate clause in a complex sentence.

A complex sentence comprises an independent clause (underlined) and at least one subordinate clause. When the subordinate clause is at the front and acts like an adverb – typically stating a time (e.g., When I was six), a place (e.g., Where I live) or a condition (e.g., If I were you) – then it is a common practice to offset it with a comma. When such a clause appears at the back, it is usually not offset with a comma.
  • When I was six, I had a wind-up Evil Knievel motorbike.
  • I had a wind-up Evil Knievel motorbike when I was six.
  • When you're on the internet,nobody knows you're a dog. (Cartoonist Peter Steiner)
This is also covered in the entries on adverbial clauses, clauses, relative clauses and restrictive clauses.

(2) Deciding whether to put a comma before a conjunction.

A compound sentence has at least two independent clauses (highlighted), which are usually joined with a conjunction (e.g., and, or, but). A conjunction (bolded) that joins two things is not normally preceded with a comma, but a conjunction that joins two independent clauses in a compound sentence is.
  • Lee likes pies and cakes.
  • (There is no comma before and. This is a simple sentence.)
  • Lee likes pies, and he likes cakes.
  • (This time, there is a comma before and. This is a compound sentence.)
  • Go, and never darken my towels again. (Comedian Groucho Marx)
  • (Remember, Go is the shortest sentence in English.)
  • I would say, "I'm alone, but I'm not lonely", but I was just kidding myself. (Actor Bruce Willis)
  • I would say, "I'm alone but not lonely", but I was just kidding myself.
  • (Compare this with the original quotation above. Here, the first but is not preceded with a comma because it's joining two adjectives (alone and not lonely) not two independent clauses.)
Often you have to look carefully for the subject and verb in the text after your conjunction to confirm the text is an independent clause. If it is, whack a comma in. If it isn't, don't use a comma.
  • Non-rabid wolves have attacked and killed people (mainly children), but this is rare. They live away from people and have developed a fear of humans from hunters and shepherds.
  • They live away from people, andthey have developed a fear of humans from hunters and shepherds.
  • (Compare this compound sentence with the simple sentence (the last one) in the example above. When you add the word they after the and, the second half becomes an independent clause, and a comma is then required.)
Be aware that a compound sentence can have more than two independent clauses.
  • Some men are born mediocre, some men achieve mediocrity, and some men have mediocrity thrust upon them. (Playwright Joseph Heller)
  • (This is a compound sentence with three independent clauses. The first independent clause ends with just a comma. This is an occasion when that's allowable.)
  • "Veni, vidi, vici" [I came, I saw,I conquered.] (Roman emperor Julius Caesar)
  • (This is another occasion when you have to say it's acceptable to use just a comma to separate independent clauses (an error also known as a comma splice). Grammarians hate the comma splice so much, you will often see "Veni, vidi, vici" translated as I came; I saw; I conquered and even I came, I saw, and I conquered.)
This is also covered in the entry on conjunctions.

(Reason 3) As the subject of an imperative sentence is "you", you can't use myself.

  • If you have any questions, email myself or your line manager. [wrong]
  • Please write to myself with any suggestions. [wrong]
The subject of an imperative sentence is "you", which is usually implied (i.e., not said or written). This means you cannot use myself, which requires the subject to be I. Writers often use myself, believing it sounds more highbrow. It's wrong. It should be me.

This is also covered in the entries on personal pronouns, reflexive pronouns and emphatic pronouns.

(Reason 4) Don't use a question mark with a declarative sentence that includes an indirect question.

  • She asked whether I loved her? [wrong]
  • I wonder if other dogs think poodles are members of a weird religious cult? [wrong] (Comedian Rita Rudner)
The bolded texts are indirect questions. These are declarative sentences (i.e., statements) not questions. They should end in full stops.

This is covered more in the entry on indirect questions.

Key Points

  • You can't write a sentence, put a comma, and then write another sentence. That's an error called a run-on sentence or comma splice.
  • If you have a fronted adverbial, use a comma.
  • Don't use a comma if your adverbial is at the back.
  • Use a comma before a conjunction (e.g., and, or, but) that joins two independent clauses.
    • I like tea but hate coffee.
    • I like tea, but I hate coffee.
  • Be careful when using myself in an imperative sentence.
    • If you're approached by any journalists, send them to myself. [wrong]
  • Don't be tempted to put a question mark at the end of a declarative sentence that contains an indirect question.
    • I wonder if John will win? [wrong]
    • (This should end in a full stop. It's not a question.)
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