Compound Sentences  

Compound Sentences

What is a compound sentence?

Compound sentences are one of the four main sentence structures. They are made up of at least two independent clauses, expressing closely related ideas of equal or similar importance that are joined together using a comma and a conjunction, a semicolon and a conjunctive adverb, or just a semicolon. By using compound sentences, we can add variety to our writing and speech and avoid the repetitive sound of multiple simple sentences.

Determining when to form a compound sentence

As mentioned, compound sentences are formed by joining two independent clauses that are closely related and of equal or similar value. To determine if two clauses can be joined in a compound sentence, we can ask ourselves three simple questions:
  • Q1. Does each clause contain a subject and a verb?
  • Q2. Can each clause stand alone to express a complete thought?
  • Q3. Are the two clauses closely related and of equal or similar importance?
If the answer to each of the three questions above is “yes,” then we can form a compound sentence. Let’s apply the three questions to an example:
  • “I like running. My sister is going to study in Sweden.”
  • Q1. Does each clause contain a subject and a verb? Yes, marked in bold.
  • Q2. Can each clause stand alone to express a complete thought? Yes.
  • Q3. Are the two clauses closely related and of equal or similar importance? No, they have nothing to do with one another.
Because the answer to question three is “no,” the two clauses above cannot be joined as a compound sentence. Let’s try another example:
  • “She wanted to play tennis. He wanted to play basketball.”
  • Q1. Does each clause contain a subject and a verb? Yes, marked in bold.
  • Q2. Can each clause stand alone to express a complete thought? Yes.
  • Q3. Are the two clauses closely related and of equal or similar importance? Yes.
Since the answer to each of the three questions is “yes,” we can form a compound sentence. This can be done in several ways. For example:
  • “She wanted to play tennis, but he wanted to play basketball.”
or:
  • “She wanted to play tennis; he wanted to play basketball.”
or:
  • “She wanted to play tennis; however, he wanted to play basketball.”

How to form a compound sentence

Once we’ve determined that two ideas can be joined to form a compound sentence, we must decide how to join them. We have several options—we can use a coordinating conjunction, a correlative conjunction, a conjunctive adverb, or a semicolon.

Forming a compound sentence using a coordinating conjunction

There are seven coordinating conjunctions in English, which can be remembered using the acronym FANBOYS:
  • For
  • And
  • Nor
  • But
  • Or
  • Yet
  • So
When we join two clauses in a compound sentence with a coordinating conjunction, we must choose the one that best fits the relationship that exists between the two clauses. For example:
  • “The family moved into the new house, and the neighbors welcomed them warmly.” (additional information)
  • “She wanted to play tennis, but he wanted to play basketball.” (contrasting information)
  • “We can go to the movies tonight, or we can just hang out at home.” (alternative choice or option)
(Punctuation note: When we use a coordinating conjunction to form a compound sentence, it is preceded by a comma, as in the examples above.)

Forming a compound sentence using a correlative conjunction

Correlative conjunctions, or paired conjunctions, are sets of conjunctions that are always used together. Since they come in pairs, with each conjunction preceding an independent clause, they can join a maximum of two independent clauses together. Some of the most common correlative conjunctions are:
  • either … or
  • just as … so
  • neither … nor
  • not … but
  • not only … but also
  • whether … or
Again, the conjunction that we choose has to do with the relationship between the two clauses. For example:
  • “Neither does he need to study, nor does he want to.” (negates both clauses)
  • “Just as baseball is loved in America, so cricket is loved in England.” (indicates that the clauses are similar)
  • “Either I will pick you up, or your father will.” (indicates two possible choices or outcomes)
Note that when we use correlative conjunctions, a comma precedes the conjunction that introduces the second independent clause, as in the examples.

Forming a compound sentence with a conjunctive adverb

Another common way to form a compound sentence is to use a conjunctive adverb. Some common conjunctive adverbs are:
  • accordingly
  • as a result
  • comparatively
  • in fact
  • moreover
  • nevertheless
  • nonetheless
  • on the other hand
  • otherwise
While coordinating conjunctions can be used to join words, phrases, or independent clauses, conjunctive adverbs can only be used to join independent clauses. Conjunctive adverbs are used to indicate a specific relationship between the two independent clauses. When we use a conjunctive adverb to form a compound sentence, it is preceded by a semicolon and followed by a comma. For example:
  • “Jen hadn’t enjoyed the play; as a result, she didn’t recommend it.” (consequence)
  • “I absolutely love singing; on the other hand, my sister hates it.” (contrast)
  • “Being a doctor is an exhausting job; moreover, you don’t earn good money until you’ve been practicing for many years.” (adding stronger information)

Forming a compound sentence with just a semicolon

If the two independent clauses are very closely related and the reader has enough information to understand the relationship between them from the context alone, we can join the clauses using a semicolon without a conjunction. For example:
  • “She wanted to play tennis; he wanted to play basketball.”
  • “I made the cake; my sister decorated it.”
  • “We don’t eat meat; we’re vegetarians.”

Using an em dash instead of a semicolon

Some writers prefer to use an em dash instead of a semicolon to join two independent clauses in a compound sentence, especially when a conjunctive adverb is not being used. This can help create a less formal or stuffy tone in one’s writing, and it is also a useful way of adding emphasis to the sentence. For example:
  • “I made the cake—my sister decorated it.” (emphasizes the contrast between the sisters’ roles)
  • “We don’t eat meat—we’re vegetarians.” (emphasizes the reason they do not eat meat)

Common errors

The most common errors that occur with compound sentences are comma splices and run-on sentences.

Comma splices

A comma splice occurs when we join two independent clauses with a comma. (A comma is not strong enough to separate two independent clauses on its own.) For example:
Luckily, the mistake is easy to correct using any of the methods for forming compound sentences that we described above. For example:

Run-on sentences

Run-on sentences can occur when we join two independent clauses without the correct punctuation or conjunction. For example:
Again, we can correct the mistake by using any of the methods described in this article:
Quiz

1. Compound sentences are made up of two (or more) ________.





2. The two parts of a compound sentence can be joined using ________.







3. Which of the following sentences is punctuated incorrectly?





4. Complete the following compound sentence with the correct conjunction:
“He’s a great rock climber; ________ , he’s a terrible skier.”





5. Complete the following compound sentence with the correct conjunction:
“I don’t mind what we do tonight. We could go bowling, ________ we could see a movie.”





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