8.3 Sentence Structure

The two essential parts of a sentence are its subject and its verb. The subject refers to the topic being discussed (or the ‘doer’ or ‘agent’ of the sentence), while the verb conveys the action or state of being expressed in the sentence (what the subject does). For example, in the short sentence “Experts debated the issue,” Experts is the subject and debated is the verb. It is important that writers be able to identify where subjects and verbs are in their sentences; knowing this gives you greater control over your language choices.
*NOTE: In technical and professional writing, it is almost always preferable to use subject-verb constructed sentences—they are the most effective way of conveying information.

Being able to identify the critical parts of a sentence and knowing the different sentence types will help you design clear and concise sentences; it will also help you improve your use of punctuation.

Sentence Types

There are four main types of sentence structures: simple, compound, complex, and compound-complex. In the examples above, Sentence 1 is a simple sentence, while Sentence 2 is complex.

SIMPLE SENTENCES have one main clause (one subject + one verb) and any number of phrases. The following are all simple sentences—try to identify the subject of each sentence and its corresponding verb:

• • • A simple sentence is very effective.
    • It makes one direct point.
    • It is good for creating emphasis and clarity.

COMPOUND SENTENCES have two or more main clauses joined by coordinating conjunctions (CC) such as for, and, nor, but, or, yet, so (a.k.a., FANBOYS). You can also connect them using a semicolon or a colon. By coordinating the ideas, you give them equal weight and importance [Subject + verb…, CC  then subject + verb].

The following sentences are all compound and are organized by subject + verb…, CC  then subject + verb:

• • • A compound sentence coordinates two ideas, and each idea is given roughly equal weight.
    • The two ideas are closely related, so they should be kept close together.
    • The two clauses may express a parallel idea, and they might also have a parallel structure.
    • Compound sentences need coordinating conjunctions, or they become comma splices, which are a type of run-on.

COMPLEX SENTENCES express complex and usually unequal relationships between ideas. One idea is “subordinated” to the main idea by using a “subordinate conjunction” (like while, because, and although); one idea is “dependent” upon the other one for logic and completeness. Complex sentences include one main clause and at least one dependent clause (see Example 2 above). Often, it is stylistically effective to begin your sentence with the dependent clause, and place the main clause at the end for emphasis.

The following sentences are complex; they each follow the same structure: Subordinate conjunction + subject + verb (the dependent clause), subject + verb (the main clause)]:

• • • When you make a complex sentence, you subordinate one idea to another.
    • If you place the subordinate clause first, you give added emphasis to the main clause at the end.

*For more information on using emphasis and subordination in your writing, see section 8.5 Using Emphasis and Subordination.

COMPOUND-COMPLEX SENTENCES have at least two main clauses and at least one dependent clause. Because a compound-complex sentence is usually quite long, you must be careful that it makes sense; it is easy for the reader to get lost in a long sentence. For more information, watch this video on compound-complex sentences from Kahn Academy.

The following sentences are compound-complex:

• • • Kate doesn’t like cartoons because they are loud, so she doesn’t watch them. (independent clause, dependent clause, coordinating conjunction, independent clause)
    • After our trip to the beach, school started back, and I was excited to see my friends. (dependent clause, independent clause, coordinating conjunction, independent clause)
    • The dog started barking, so the cat ran away, and since I couldn’t keep up, I decided to stop. (independent clause, coordinating conjunction, independent clause, coordinating conjunction, dependent clause, independent clause)

Complete this short activity to test your knowledge of sentence types: 

Chapter 8 Exercise: Sentence Types

Additional Resources

• “Sentence Structure of Technical Writing” from MIT’s The Mayfield Handbook of Technical Scientific Writing

• “Sentence Patterns” handout

"Sentence Structure." Technical Writing Essentials. [License: CC BY-SA]