OCHAKS

Sentences:  Simple, Compound, and Complex Experienced writers use a variety of sentences to make their writing interesting and lively. Too many simple sentences, for example, will sound choppy and immature while too many long sentences will be difficult to read and hard to understand. 
This page contains definitions of simple, compound, and complex sentences with many simple examples.  The purpose of these examples is to help the ESL/EFL learner to identify sentence basics including identification of sentences in the short quizzes that follow.   After that, it will be possible to analyze more complex sentences varieties. 
SIMPLE SENTENCE
A simple sentence, also called an independent clause, contains a subject and a verb, and it expresses a complete thought. In the following simple sentences, subjects are in yellow, and verbs are in green.  

The three examples above are all simple sentences.  Note that sentence B contains a compound subject, and sentence C contains a compound verb.  Simple sentences, therefore, contain a subject and verb and express a complete thought, but they can also contain a compound subjects or verbs. 
COMPOUND SENTENCE
A compound sentence contains two independent clauses joined by a coordinator. The coordinators are as follows: for, and, nor, but, or, yet, so. (Helpful hint: The first letter of each of the coordinators spells FANBOYS.) Except for very short sentences, coordinators are always preceded by a comma. In the following compound sentences, subjects are in yellow, verbs are in green, and the coordinators and the commas that precede them are in red. 
The above three sentences are compound sentences.  Each sentence contains two independent clauses, and they are joined by a coordinator with a comma preceding it.  Note how the conscious use of coordinators can change the relationship between the clauses.  Sentences B and C, for example, are identical except for the coordinators.  In sentence B, which action occurred first?  Obviously, "Alejandro played football" first, and as a consequence, "Maria went shopping.  In sentence C, "Maria went shopping" first.  In sentence C, "Alejandro played football" because, possibly, he didn't have anything else to do, for or because "Maria went shopping."  How can the use of other coordinators change the relationship between the two clauses?  What implications would the use of "yet" or "but" have on the meaning of the sentence?
COMPLEX SENTENCE
A complex sentence has an independent clause joined by one or more dependent clauses. A complex sentence always has a subordinator such as because, since, after, although, or when or a relative pronoun such as that, who, or which. In the following complex sentences, subjects are in yellow, verbs are in green, and the subordinators and their commas (when required) are in red.
When a complex sentence begins with a subordinator such as sentences A and D, a comma is required at the end of the dependent clause. When the independent clause begins the sentence with subordinators in the middle as in sentences B, C, and E, no comma is required. If a comma is placed before the subordinators in sentences B, C, and E, it is wrong.
Note that sentences D and E are the same except sentence D begins with the dependent clause which is followed by a comma, and sentence E begins with the independent clause which contains no comma.  The comma after the dependent clause in sentence D is required, and experienced listeners of English will often hear a slight pause there.  In sentence E, however, there will be no pause when the independent clause begins the sentence. 
COMPLEX SENTENCES / ADJECTIVE CLAUSES
Finally, sentences containing adjective clauses (or dependent clauses) are also complex because they contain an independent clause and a dependent clause.  The subjects, verbs, and subordinators are marked the same as in the previous sentences, and in these sentences, the independent clauses are also underlined. 

A. The woman who called my mom sells cosmetics. B. The book that Jonathan read is on the shelf. C. The house which Abraham  Lincoln was born in is still standing. D. The town where I grew up is in the United States.

Adjective Clauses are studied in this site separately, but for now it is important to know that sentences containing adjective clauses are complex.
CONCLUSION
Are sure you now know the differences between simple, compound, and complex sentences?  Click QUICK QUIZ to find out.  This quiz is just six sentences.  The key is to look for the subjects and verbs first.
Another quiz, this one about Helen Keller contains ten sentences.
These quiz sentences based on the short story, The Americanization of Shadrach Cohen, by Bruno Lessing.
Quick Quiz:  Shadrach
After each quiz, click GRADE QUIZ to see your score immediately. 
Remember that with the skill to write good simple, compound, and complex sentences, you will have the flexibility to (1) convey your ideas precisely and (2) entertain with sentence variety at the same time!  Good luck with these exercises!