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SPARK: Sentence Structure

A resource for students wanting to improve their academic and research skills.

Sentence Structure

The most important quality of a sentence is that it clearly communicate the writer’s meaning to the reader.

Using appropriate style and grammar is important because it contributes to clarity. Clarity is also affected by various elements of sentence structure such as sentence complexity, punctuation and verb tense.

Review the sections below to view some common issues that arise concerning sentence structure and clarity. You can also review the "Creating Complex Sentences" document located in the 'Resources' tab. 


Sentences have subjects and verbs; if you lack one or the other, the meaning of your sentence might be unclear. We call sentences that lack subjects or verbs 'sentence fragments' are, while they sometimes occur in creative writing pieces, they are not appropriate for an academic essay. Sentences must normally have both a subject and a verb, that is, an actor and an action. If one or the other is missing, the result is a sentence fragment.

Examples of fragments include:

No verb/action:

  • The busy summer streets of Santiago.
  • Literary critics with a penchant for bourbon.

What you can see here is that while we know the sentences are about the streets of Santiago or the literary critics who like bourbon, we have no idea what these people or doing.

No subject/actor:

  • That never saw the light of day.
  • Turning with little interest and a heavy heart.

What you can see here is that though we know what is happening (never seeing the light of day, or turning with a heavy heart) we don't know who is doing these things, so this also isn't a full sentence. 

At the other extreme, neither should a sentence run on line after line without a period; readers will not be able to keep up.  Running many ideas together in one sentence haphazardly can easily cause a reader to stumble over the meaning of the sentence. When you're writing, you always want to try to make things as easy for your reader to follow as you possibly can. 

An example would be:

  • The lawyer was taken aback by her client’s description of the accident scene where she had not seen that many cars in one heap that her head was swimming.

What you can see here is that it's pretty difficult to figure out who is the actor (the person doing the thing) and what the action is because there are so many things happening at once. Break these long sentences up into smaller ones so that your reader can figure out what is happening.



Writing about complex ideas frequently requires building complex sentences with multiple clauses. Punctuation can be helpful in keeping the meaning of complex sentences clear, but errors in punctuation can increase a reader’s problems considerably.

For suggestions about how to keep the relationship between two ideas clear for a reader through correct use of a few simple words, see Creating Complex Sentences located in Resources.


Personal pronouns are a wonderful tool for avoiding the need to constantly repeat the name of a person or group. However, if a writer is not careful when using personal pronouns, a reader will have trouble determining who is meant by “he,” “them,” or other pronouns used in the essay. Particularly problematic is placing the pronoun “this” at the beginning of a sentence without a clear indication of what “this” means.

Here are examples of sentences in which it is unclear what is meant by the pronouns “he,” “them,” and “this”:

  • Raj looked carefully at Edwin because he had never been this sad. (Who is sad—Raj or Edwin?)
  • Jelena raised rabbits with her parents, and her teacher asked if she would bring them to school one day. (Who does “them” refer to—her parents or her rabbits?)
  • When parents try to ignore inappropriate attempts to gain their attention, children often escalate to more extreme tactics. This prompts considerable anxiety. (What prompts the anxiety—trying to ignore the children or the children’s extreme tactics?)

As you can see, relying too much on personal pronouns can really make it difficult for your reader to figure out what you are trying to say.

Verb Tense

Readers are often confused by changes in verb tense from one part of an essay to another.

Generally speaking, if you start writing a paragraph in the present tense, you should not switch to the past tense or future tense within that paragraph unless doing so aids the communication of your meaning.

Shifting from one verb tense to another anywhere in your essay should only be done when your ideas or argument clearly require it.

Example of tense switch within a sentence:

  • Darwin traveled to the Galapagos Islands on his ship, the Beagle, where he observes many varieties of finches. 

This sentence beings in the past tense (traveled) and then moves to the present tense (observes) for no reason. Sometimes you might need to change tenses, but don't do it in the middle of a sentence.