APPENDICES: Academic Writing Basics

Appendix E: Sentence Structure

When building anything, it is important to be familiar with the tools you are using.  Grammatical elements are the main “tools” you use when when building sentences and longer written works.  Thus, it is critical to have some understanding of grammatical terminology in order to construct effective sentences. If you would like to a review some basic parts of speech (nouns, pronouns, articles, adjectives, adverbs, verbs, conjunctions, prepositions, etc), see the Parts of Speech Overview at the OWL.

The two essential parts of a sentence are the subject and the predicate (verb portion). The subject refers to the topic being discussed while the verb conveys the action or state of being expressed in the sentence. All clauses must contain both a subject and a verb; phrases, on the other hand, lack one or both a subject and a verb, so they need to relate to or modify other parts of the sentence. Main clauses, also called independent clauses, can stand on their own and convey an idea. Dependent clauses, also called subordinate clauses, rely on another part of the sentence for meaning and can’t stand on their own.

Consider the following examples:

The engineers stood around the table looking at the schematics for the machine.

Sentence 1 is a simple sentence. It has one clause, with one subject (The engineers) and one verb (stood). These are followed by 3 modifying phrases (“around the table” “looking at the schematics” and “for the machine”).

After they discussed different options, they decided to redesign the components.

Sentence 2 is a complex sentence, with one dependent and one independent clause, each with its own subject-verb combination (“they discussed” and “they decided”). The two clauses are joined by the subordinate conjunction, “after,” which makes the first clause subordinate to (or dependent upon) the second one.

Being able to identify the critical parts of the sentence will help you design sentences that have a clear and effective subject-verb relationship. Knowing the components will also help you improve your punctuation. If you would like a more detailed review of sentence structure, visit Purdue’s  OWL (Online Writing Lab) Mechanics page.

Sentence Structures

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:

  • A simple sentence can be very effective.
  • It makes one direct point.
  • It is good for creating emphasis and clarity.
  • Too many in a row can sound repetitive and choppy.
  • Varied sentence structure sounds more natural.

COMPOUND SENTENCES have two or more main clauses joined by coordinating conjunctions (CC) such as and, but, for, yet, nor, or, so (FANBOYS). You can also connect them using punctuation such as a semi-colon or a colon. By coordinating the ideas, you are giving them roughly equal weight and importance.

Subject + verb,    CC    Subject + verb
The following sentences are all compound:
  • A compound sentence coordinates two ideas, and each idea is given roughly equal weight.
  • The two ideas are closely related, so you don’t want to separate them with a period.
  • The two clauses make up part of the same idea; thus, they should be part of the same sentence.
  • The two clauses may express a parallel idea; they might also have a parallel structure.
  • You must remember to include the coordinate conjunction, or you may commit a comma splice.

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” or “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.

Subord. Conjunction + subject + verb (this is the dependent clause),    Subject + verb (this is the main clause)

The following are all examples of complex sentences:

  • 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.
  • Subordinate clauses cannot stand on their own. Despite the fact that many students try to use them that way. x (fragment – replace the period with a comma to fix this error)

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.


Using a variety of sentence types as well as using these types strategically to convey your ideas will strengthen your style.  Keep the following in mind:

  • Simple sentences are great for emphasis.  The make great topic sentences.
  • Compound sentences balance ideas; they are great for conveying the equal importance of related ideas.
  • Complex sentences, when you use them effectively, show complicated relationships between ideas by subordinating one idea to another.

EXERCISE Combining sentences

Combine the following pairs of sentences to make one idea subordinate to the other. Notice the impression you convey by how you subordinate one idea to another. If your combined sentence was a topic sentence for a paragraph, what idea would the reader expect that paragraph to emphasize?

  1. Pair 1.
    • Energy drinks enhance awareness and energy level.
    • Energy drinks have negative health impacts.
  2. Pair 2.
    • Smith’s study found that energy drinks can increase athletic endurance.
    • The study also found that energy drinks can cause negative side effects such as headaches and “energy crashes”, and can possibly lead to caffeine addiction.
  3. Pair 3.
    • The rates of adolescent male violence has dropped by 20% over the last decade.
    • The rates of female adolescent violence has increased by 50% over the last decade.
  4. Pair 4.
    • Nuclear power plants can pose significant dangers.
    • Nuclear energy is a clean and efficient way to generate power and reduce reliance on fossil fuels.


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Technical Writing Essentials Copyright © 2019 by Suzan Last is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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