Definition of Compound Sentences and How to Use Them

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In a writer's toolkit, few things are more versatile than the compound sentence. These sentences are more complex than a simple sentence because they contain two or more independent clauses instead of the typical one. Compound sentences give an essay detail and depth, making writing come alive in the reader's mind.

What Is a Compound Sentence?

In English grammar, a compound sentence is two (or more) simple sentences joined by a conjunction or an appropriate mark of punctuation. Both sides of a compound sentence are complete on their own, but more meaningful when connected. The compound sentence is one of the four basic sentence structures. The others are the simple sentence, the complex sentence, and the compound-complex sentence.

Components of a Compound Sentence

Compound sentences can be constructed in a number of ways. Regardless of how you structure a compound sentence, it signals to the reader that you are discussing two equally important ideas. There are three primary methods of building a compound sentence: the use of coordinating conjunctions, the use of semicolons, and the use of colons.

Coordinating Conjunctions

A coordinating conjunction indicates a relationship between two independent clauses that are contrasting or complementary. It is by far the most common means of joining clauses to create a compound sentence.

Example: Laverne served the main course, and Shirley poured the wine.

Spotting a coordinating conjunction is fairly easy because there are only seven to remember: for, and, nor, but, or, yet, and so (F.A.N.B.O.Y.S.).

Semicolons

A semicolon creates an abrupt transition between two clauses, usually for sharp emphasis or contrast.

Example: Laverne served the main course; Shirley poured the wine.

Because semicolons build a very direct rather than fluid transition, use them sparingly. You can write a perfectly good essay without a single semicolon, but using them here and there can vary your sentence structure and make for more dynamic writing.

Colons

In more formal writing, a colon may be employed to show a hierarchical (in significance, time, order, etc.) relationship between clauses. 

Example: Laverne served the main course: It was time for Shirley to pour the wine.

Using a colon in a compound sentence is rare in everyday English as colons are mostly used to introduce lists. You're most likely to encounter this use in complex technical writing.

Simple vs. Compound Sentences

On some occasions, you may be unsure of whether the sentence you're reading is simple or compound. An easy way to find out is to try dividing the sentence into two distinct sentences (do this by looking for coordinating conjunctions, semicolons, or colons).

If the result makes sense, then you've got a compound sentence with more than one independent clause. If it doesn't, then you've likely just tried to split a clause and you're dealing with a single simple sentence, which contains one independent clause but may be accompanied by dependent clauses or phrases as well.

Simple: I was late for the bus. The driver had already passed my stop.

Compound: I was late for the bus, but the driver had already passed my stop.

Sentences that can't be split without ruining grammar or meaning are simple sentences, and these may or may not contain subordinate or dependent clauses in addition to an independent clause.

Simple: When I left the house, I was running late. (When I left the house is the subordinate clause).

Compound: I left the house; I was running late.

Another way to determine whether a sentence is simple or compound is to look for verb phrases or predicate phrases. These phrases cannot stand alone and are not considered to be clauses.

Simple: Running late, I decided to take the bus. (Running late is the verb phrase).

Compound: I was running late, so I decided to take the bus.