Understanding and using different types of sentence structure helps us to add variety and interest to our writing.

There are four broad types of sentence structure in English: simple, compound, complex and compound-complex. This article focuses on compound sentences.

What is a compound sentence?

A compound is something made up of two or more parts. A compound sentence is a sentence formed from two or more simple sentences (or independent clauses).

For example, here are two simple sentences:

Megan cut the wood.
Ryan stacked it.

Each one is an independent clause (IC), that is, a word group that contains a subject and a verb and can stand alone. Although these sentences are grammatically correct, too many simple sentences can make our writing sound dull.

You can solve the problem by combining simple sentences into a compound sentence:

Megan cut the wood, and Ryan stacked it. (IC + IC)

Note: The two clauses forming the compound sentence must be related in meaning. Because of the logical connection between the two clauses in the previous example, they fit together in one sentence. It would not be logical to join two sentences with unrelated meanings. For example, it would sound odd to say Megan cut the wood, and a seagull flew by.

Are there different ways to form a compound sentence?

Yes, there are three different methods you can use to join independent clauses in a compound sentence.

Method 1: Use a comma and a coordinating conjunction

A coordinating conjunction is one of these seven joining words: for, and, nor, but, or, yet and so. You can remember the coordinating conjunctions with the word fanboys, formed from the first letters of these seven conjunctions.

We can use a comma and a coordinating conjunction (cc) to join two or more independent clauses (IC) into a compound sentence. Note that the comma comes before the conjunction, not after it. The sentence has the structure IC + cc + IC.

The first example we saw illustrates this structure, using the conjunction and:

Megan cut the wood, and Ryan stacked it.

BUT

Megan cut the wood and stacked it.

In the second example, the conjunction and is joining two verbs instead of two independent clauses. Therefore, the sentence is not compound, and no comma is used before the conjunction.

Here are some more examples of compound sentences:

F The two stopped to eat, for the work had made them hungry.

A The afternoon had been long, and hours had gone by since lunch.

N There was no house nearby, nor did they have any food with  them.

B They wanted to pick blueberries as a snack, but a bear growled at them from the berry patch.

O Should they leave now, or should they wait awhile?
(Comma optional—see note)

Y The job was not done, yet they needed to rest and eat.

S They were starving, and it was getting dark, so they went home.

Note: If the independent clauses are short, parallel and closely related, it is acceptable to use only a comma or a conjunction to join them:

Megan cut the wood, Ryan stacked it.

OR

Megan cut the wood and Ryan stacked it.

But between longer clauses, it is important to use both a comma and a conjunction:

Megan cut the wood into one-and-a-half-foot logs, and Ryan stacked them carefully along the rear of the cabin.

If you used a comma alone in the above example, you would have a comma splice, a type of run-on sentence. Since it is never wrong to use a comma and conjunction together in this kind of compound sentence, it is best to do so in every case to avoid the risk of error.

Method 2: Use a semicolon

A semicolon (sc), like a period, creates a stop between two independent clauses. However, the clause after the semicolon does not begin with a capital (unless the first word is a proper noun). In this case, the sentence has the structure IC + sc + IC.

This method works readily with some of the examples:

Megan cut the wood; Ryan stacked it.

The two stopped to eat; the work had made them hungry.

However, it would be awkward to use a semicolon by itself to form some compound sentences. The sentence below, for example, doesn’t make sense:

Incorrect: The job was not done; they needed to rest and eat.

Correct: The job was not done, but they needed to rest and eat.

These two clauses express contrasting ideas. We need a contrast word to make the connection clear. In this case, you might use the contrast conjunction but with a comma, or you might decide to use Method 3.

Method 3: Use a semicolon with a transitional expression

A transitional expression shows the relationship between two ideas. A semicolon with a transitional expression often makes a smoother connection than a semicolon alone.

There are many transitional expressions showing different kinds of relationships. Here are a few common examples:

Addition: also, in addition, moreover

Contrast: however, in contrast, on the other hand

Result: therefore, as a result, consequently

Example: for example, for instance

Listing: first, second, third

Note that a comma is used after the transitional word or expression. The sentence has the structure IC + sc + transition + IC:

The work had made them hungry; therefore, they stopped to eat.

The job was not done; on the other hand, they needed to rest and eat.

Note: A transitional word is not a conjunction; it does not join sentences grammatically. Therefore, the usual punctuation is a period or semicolon before it:

They wanted to pick blueberries as a snack. However, a bear growled at them from the berry patch.

OR

They wanted to pick blueberries as a snack; however, a bear growled at them from the berry patch.

If you use a comma instead of a period or semicolon, you have a comma splice run-on.

Run-on: They wanted to pick blueberries as a snack, however, a bear growled at them from the berry patch.

Be careful to avoid this type of run-on; it is a very common error.