Improving Your Sentence Structure

To improve your academic writing skills, you must first understand possible problems with sentence structure so that you can not only recognize but write effective sentences.

To understand sentences, you must first understand clauses, which make up sentences. A clause is defined as a group of words containing both a subject and a verb.

Clauses can be independent or dependent.

  • An independent clause contains both a subject and a verb and can stand alone as a sentence.
  • A dependent clause contains both a subject and a verb, but cannot stand alone as a sentence.
    Dependent clauses are introduced by subordinating conjunctions such as because, that, what, while, who, which, although, if, etc.

Kinds of Sentences

There are three kinds of sentences:


  1. SIMPLE: A simple sentence consists of one main (or independent) clause. To be complete, a simple sentence must have at least one SUBJECT and one 'verb'.
    The MAN  'went'  to the store.
    A simple sentence may also have a compound subject and/or a compound verb. 
    The MAN and his SON 'went' to the store and 'bought' some milk.
  2. COMPOUND: A compound sentence has at least two main (or independent) clauses, connected by coordinating conjunctions (such as and, but, or, nor, for, so, yet). Each clause has its own subject(s) and verb(s). The second clause should be separated from the first by a comma in front of the coordinating conjunction.
    The man went to the store, and the sales clerk sold him some milk.
  3. COMPLEX: A complex sentence has one main (or independent) clause and one or more dependent (or subordinate) clauses.
    When an atom is split, it releases neutrons.

    Dependent clauses can function in the sentence as nouns, adjectives or adverbs:

  • NOUN CLAUSES function as nouns in the sentence and can be used as subjects, objects, predicate nominatives, and objects of prepositions. 
    WHAT IS MOST IMPORTANT TO HIM is his family. (subject) That critic writes THAT AL PURDY IS THE BEST POET IN CANADA. (object)
    You are WHAT YOU EAT. (predicate nominative)
    She is very suspicious about WHAT HE SAID. (object of preposition about)
  • ADJECTIVE CLAUSES start with a relative pronoun( such as who, which, or that) and function as adjectives.
    The pronoun refers to a noun that usually precedes it directly. 
    The woman WHO BOUGHT THE RED DRESS is my aunt. That dress, WHICH IS MY FAVOURITE, was expensive. The problem THAT HE SOLVED was a difficult one.

    NOTE: Use commas around the adjective clause to indicate that the information there is not essential to the sentence, i.e., not needed to identify the subject (see Improving Your Punctuation).
    Absence of commas, on the other hand, indicates the information is essential to the sentence. 
    The bull that is in the pasture belongs to Joe. (suggests that, of all the other bulls on the farm, the one in the pasture is being identified as belonging to Joe)


    The bull, which is in the pasture, belongs to Joe. (suggests that there is only one bull on the farm, so the writer is giving non-essential information by mentioning that it is in the pasture)

    NOTE: The word THAT is used to introduce an essential clause (without commas), whereas WHICH is used to introduce a non-essential clause (with commas). Some grammar textbooks suggest WHICH can be used for either essential or non-essential clauses.
    NOTE: A pronoun (such as which, that) must always refer specifically to one noun. The word WHICH is often used incorrectly.
    Your essays should be submitted on time, WHICH is one way to be a successful student.
    (Vague reference because the word which in this sentence refers to neither time nor essays.)
    One way for you to be successful as a student is to submit your essays on time.

  • ADVERB CLAUSES function as adverbs in the sentence, modifying verbs, adjectives, or adverbs. They may tell how, why, when, where, etc.
    Conjunctions used include although, after, if, because, while, since, whether, etc. 
    WHEN I ARRIVED AT THE UNIVERSITY, classes had already started.
    ALTHOUGH BOB IS INTELLIGENT, he doesn’t work very hard.

Problems with Sentences

1. Sentence Fragments

A sentence fragment is not a complete sentence. It usually lacks either a subject or a verb, or both, or contains only a dependent clause. 

For example, three dogs and a goat. (no verb – what did the animals do?)
Studying too hard on weekends. (no subject – who was studying?)
Because I couldn’t find my shoes. (contains a subject and verb, but is a dependent clause)

2. Run-on Sentences: Fused Sentences and Comma Splices

A run-on sentence is one in which two or more independent clauses are inappropriately joined. Remember that the length of a sentence does not determine whether it is a run-on sentence: a sentence that is correctly punctuated and correctly joined can be extremely long. Two types of run-on sentences are fused sentences and sentences with comma splice errors.

  • In a fused sentence, clauses run into each other with no punctuation. 
    The experiment failed it had been left unobserved for too long.
  • A comma splice refers to the error of placing only a comma between two complete sentences, without a connecting word (such as and, but, or because).
    The experiment failed, it had been left unobserved for too long.

To correct a fused sentence or a comma splice error, you can use either a period, semi-colon, colon, coordinating conjunction, or subordinating conjunction. 

The experiment failed. It had been left unobserved for too long.
The experiment failed; it had been left unobserved for too long.
The experiment failed: it had been left unobserved for too long.
The experiment had been left unobserved for too long, SO it failed.
The experiment failed BECAUSE it had been left unobserved for too long.

  • A comma splice also occurs when commas are used before conjunctive adverbs (therefore, however, nevertheless, moreover, etc.) connecting two sentences. 
    The experiment had been left unobserved for too long, therefore it failed.
    The experiment had been left unobserved for too long; therefore, it failed.
    He wasn’t prepared to defend a client who was guilty; however, he could be persuaded to accept a bribe.

    NOTE: When the conjunctive adverb is within the clause rather than at the beginning, place it between commas.
    He wasn’t prepared to defend a client who was guilty; he could be persuaded, however, to accept a bribe.

3. Loose Sentences

  • A loose sentence may result if you use too many “and ” connectives when other conjunctions would convey a more precise meaning. 
    John had a weight problem, and he dropped out of school. (what is the most accurate connection: John had a weight problem so he dropped out of school or because he dropped out of school?)
  • A loose sentence also results from weak sentence construction and the inclusion of many phrases and clauses in no particular order.
    In the event that we get the contract, we must be ready by June 1 with the necessary personnel and equipment to get the job done, so with this end in mind a staff meeting, which all group managers are expected to attend, is scheduled for February 12.

    NOTE: Writing the previous passage as several sentences would be more effective.

4. Choppy Sentences

A succession of short sentences, without transitions to link them to each other, results in choppy sentences. 

Our results were inconsistent. The program obviously contains an error. We need to talk to Paul Davis. We will ask him to review the program.
We will ask Paul Davis to review the program because it produced inconsistent results.

5. Excessive Subordination

Excessive subordination is not an effective substitute for choppiness. 

Doug thought that he was prepared but he failed the examination which meant that he had to repeat the course before he could graduate which he didn’t want to do because it would conflict with his summer job.
Doug thought that he was prepared, but he failed the examination. Therefore, he would have to repeat the course before he could graduate. He did not want to do that because it would conflict with his summer job.

6. Parallel Structure

Parts of a sentence which are in sequence must all follow the same grammatical or structural principle. 

I like to swim, to sail, and rowing.
I like to swim, to sail, and to row.
I like swimming, sailing, and rowing.
This report is an overview of the processes involved, the problems encountered, and how they were solved.
This report is an overview of the processes involved, the problems encountered, and the solutions devised.