Sentence formation is one of the key ingredients to good writing. There are several forms of sentences you can use in your writing — simple, compound, complex and compound-complex — and knowing how to use all of them will allow you to express your ideas with clarity and in great detail. You'll also be able to add variety to your work to keep the reader interested.
Before you start writing compound-complex sentences, you'll need to understand the two types of clauses in a sentence. A clause is any portion of a sentence that includes a subject and a verb.
The word “clause” itself does not necessarily describe a complete sentence. However, simple sentences are made of an independent clause, which can stand alone as a complete sentence. For example:
- Erin loves her brother.
- The dog ran off.
- I am tall.
Each of the sentences above has a subject and verb, and it stands by itself as a complete idea. This is an independent clause or a complete simple sentence.
The other kind of clause is a dependent clause. These are not complete sentences, but they do contain a noun and a verb. For example:
- When I come home
- If you sell the most cookies
- Because she is so smart
Notice that each of these clauses begins with a relative pronoun. This is the word that turns an independent clause into a dependent clause that must be attached to another independent clause. It cannot stand alone. You need more information to complete the thought.
Compound sentences are formed by combining two independent clauses. For example:
- Erin loves her brother, and he loves her too.
- The dog ran off, but I didn't care.
- I am tall, yet she is short.
Note that when independent clauses are joined, they need a coordinating conjunction between them. Coordinating conjunctions include the following words: for, and, nor, but, or, yet, so.
When you write a compound sentence, you need to use a comma before the coordinating conjunction to punctuate your sentence correctly.
When a dependent clause is joined to an independent clause, it forms a complex sentence. The dependent clause can come either at the beginning or the end of the sentence. For example:
- When I come home, I will eat dinner.
- If you sell the most cookies, you will win the prize.
- The college gave her a scholarship because she is so smart.
Note that when you place the dependent clause at the beginning of the sentence, you need to put a comma after it. When the dependent clause is at the end of the sentence, no comma is required.
As the name suggests, a compound-complex sentence brings both of these sentence forms together. That is, it contains at least two independent clauses (like a compound sentence) and at least one dependent clause (like a complex sentence). For example:
- Erin loves her brother, and he loves her too because she pays his bills.
- The dog ran off when I chased him, but I didn't care.
- Though my mother says it doesn't matter, I am tall, and she is short.
Note that the dependent clause can be at the beginning, middle, or end of a compound-complex sentence. No matter where it is placed, the punctuation follows the rules for both compound sentences and complex sentences.
That means that you need to put a comma before the coordinating conjunction and, if applicable, another comma after the dependent clause when it occurs at the beginning of the sentence.
See some additional examples to get a feel for how compound-complex sentences will help you add detail to your writing:
- When I went to the store, my parents wanted me to pick up some milk, but I didn't have enough money.
- Even if the child is hungry, he will never eat oatmeal, but he will always eat ice cream.
- The man was mean because he was lonely, but his attitude only made his situation worse.
- The dog needed a new leash, and he couldn't go for a walk until he had one.
- It is important to vote when the time comes, or you won't get a say in new laws.
Writing compound-complex sentences allows you a great deal of flexibility to explain how, why or when something happened. It's important to understand which parts of the sentence are independent clauses and which are dependent clauses so that you can punctuate it correctly and avoid writing a run-on sentence. Once you master this, you can freely add them to your writing to express more complicated ideas with clarity.
For more information on types of sentences and sentence structure, take a look at our sentence variety examples. They will show you how using varied sentence types and combining sentences add impact to your writing.