Simple? Compound? Complex?

A simple sentence consists of one independent clause (also called a "main clause").

A compound sentence has two or more independent clauses.

A complex sentence has one independent clause and one or more dependent clauses (also called "subordinate clauses").

A compound-complex sentence has two or more independent clauses and one or more dependent clauses.

Notice that the compound-complex sentence is simply a sentence that is both compound (2 or more independent clauses) and complex (1 or more dependent clauses). It is not always treated as a separate type.

We might visualize these definitions this way*:

An independent clause can be identified by the fact that it can be changed into a single yes/no question without deleting any words or adding any words except, possibly, the auxiliary verb do:

This is a simple web page.         Is this a simple web page?

If there are two independent clauses (i.e., if the sentence is compound), there will be two yes/no questions:

Mary had a little lamb, and it followed her to school.              Did Mary have a little lamb?  Did it follow her to school? (Sometimes the questions will make sense as a compound, joined by the same coordinating conjunction used in the original sentence: Did Mary have a little lamb, and did it follow her to school? Sometimes this won't work, or will be so awkward it seems ungrammatical.)

A dependent clause simply becomes part of the yes/no question formed from the independent clause:

Mary had a little lamb that followed her to school.            Did Mary have a little lamb that followed her to school?

Notice that if we try to make that followed her to school into a yes/no question, we have to omit that and insert it to make the result grammatical: 

That followed her to school              *Did that follow her to school?  (Did it follow her to school?)

  A compound sentence must have either a coordinating conjunction or a semicolon (or possibly a dash or colon) between the independent clauses. Inserting a comma instead creates a comma splice, and using no joining at all creates a fused or run-on sentence.

The links below go to pages that provide both explanations of these terms and interactive exercises that let you practice applying the definitions. (Remember that compound-complex sentences may be seen as a combination rather than a fourth separate type.)

	Sentences: simple and compound and Sentences: complex and compound-complex (This fairly detailed tutorial has interactive exercises embedded within it. Highly recommended!)
	Compound/Complex Sentences The exercises here are not interactive, but the answers are given.
	Clauses: The Essential Building Blocks is part of the excellent Guide to Grammar and Writing site. Interactive exercises are built into a detailed discussion of clauses, and another page has basic definitions and an interactive quiz on sentence types.

* Thanks to Daniel Younts, ENG 332101, Fall 2006, for the idea for this way of seeing this material!

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