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Finding Common Errors

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Proofreading is primarily about searching your writing for errors, both grammatical and typographical, before submitting your paper for an audience (a teacher, a publisher, etc.). Use this resource to help you find and fix common errors.

Here are some common proofreading issues that come up for many writers. For grammatical or spelling errors, try underlining or highlighting words that often trip you up. On a sentence level, take note of which errors you make frequently. Also make note of common sentence errors you have such as run-on sentences, comma splices, or sentence fragments—this will help you proofread more efficiently in the future.


  • Do not solely rely on your computer's spell-check—it will not get everything!
  • Trace a pencil carefully under each line of text to see words individually.
  • Be especially careful of words that have tricky letter combinations, like "ei/ie.”
  • Take special care of homonyms like your/you're, to/too/two, and there/their/they're, as spell check will not recognize these as errors.

Left-out and doubled words

Read the paper slowly aloud to make sure you haven't missed or repeated any words. Also, try reading your paper one sentence at a time in reverse—this will enable you to focus on the individual sentences.

Sentence Fragments

Sentence fragments are sections of a sentence that are not grammatically whole sentences. For example, “Ate a sandwich” is a sentence fragment because it lacks a subject.

Make sure each sentence has a subject:

  • “Looked at the OWL website.” is a sentence fragment without a subject.
  • “The students looked at the OWL website.” Adding the subject “students” makes it a complete sentence.

Make sure each sentence has a complete verb.

  • “They trying to improve their writing skills.” is an incomplete sentence because “trying” is an incomplete verb.
  • “They were trying to improve their writing skills.” In this sentence, “were” is necessary to make “trying” a complete verb.

See that each sentence has an independent clause. Remember that a dependent clause cannot stand on its own. In the following examples, green highlighting indicates dependent clauses while yellow indicates independent clauses.

  • Which is why the students read all of the handouts carefully.” This is a dependent clause that needs an independent clause. As of right now, it is a sentence fragment.
  • Students knew they were going to be tested on the handouts, which is why they read all of the handouts carefully.” The first part of the sentence, “Students knew they were going to be tested,” is an independent clause. Pairing it with a dependent clause makes this example a complete sentence.

Run-on Sentences

  • Review each sentence to see whether it contains more than one independent clause.
  • If there is more than one independent clause, check to make sure the clauses are separated by the appropriate punctuation.
  • Sometimes, it is just as effective (or even more so) to simply break the sentence into two separate sentences instead of including punctuation to separate the clauses.


  • Run on: “I have to write a research paper for my class about extreme sports all I know about the subject is that I'm interested in it.” These are two independent clauses without any punctuation or conjunctions separating the two.
  • Edited version: "I have to write a research paper for my class about extreme sports, and all I know about the subject is that I'm interested in it." The two highlighted portions are independent clauses. They are connected by the appropriate conjunction “and,” and a comma.
  • Another edited version: “I have to write a research paper for my class about extreme sports. All I know about the subject is that I'm interested in it.” In this case, these two independent clauses are separated into individual sentences separated by a period and capitalization.

Comma Splices

  • Look closely at sentences that have commas.
  • See if the sentence contains two independent clauses. Independent clauses are complete sentences.
  • If there are two independent clauses, they should be connected with a comma and a conjunction (and, but, for, or, so, yet, nor). Commas are not needed for some subordinating conjunctions (because, for, since, while, etc.) because these conjunctions are used to combine dependent and independent clauses.
  • Another option is to take out the comma and insert a semicolon instead.


  • Comma Splice: “I would like to write my paper about basketball, it's a topic I can talk about at length.” The highlighted portions are independent clauses. A comma alone is not enough to connect them.
  • Edited version: “I would like to write my paper about basketball because it's a topic I can talk about at length.” Here, the yellow highlighted portion is an independent clause while the green highlighted portion is a dependent clause. The subordinating conjunction “because” connects these two clauses.
  • Edited version, using a semicolon: “I would like to write my paper about basketball; it’s a topic I can talk about at length.” Here, a semicolon connects two similar independent clauses.

Subject/Verb Agreement

  • Find the subject of each sentence.
  • Find the verb that goes with the subject.
  • The subject and verb should match in number, meaning that if the subject is plural, the verb should be as well.
  • An easy way to do this is to underline all subjects. Then, circle or highlight the verbs one at a time and see if they match.


  • Incorrect subject verb agreement: “Students at the university level usually is very busy.” Here, the subject “students” is plural, and the verb “is” is singular, so they don’t match.
  • Edited version: “Students at the university level usually are very busy.” “Are” is a plural verb that matches the plural noun, “students.”

Mixed Construction

Read through your sentences carefully to make sure that they do not start with one sentence structure and shift to another. A sentence that does this is called a mixed construction.


  • Since I have a lot of work to do is why I can't go out tonight.” Both green highlighted sections of the sentence are dependent clauses. Two dependent clauses do not make a complete sentence.
  • Edited version: “Since I have a lot of work to do, I can't go out tonight.” The green highlighted portion is a dependent clause while the yellow is an independent clause. Thus, this example is a complete sentence.


Look through your paper for series of items, usually separated by commas. Also, make sure these items are in parallel form, meaning they all use a similar form.

  • Example: “Being a good friend involves listening, to be considerate, and that you know how to have fun.” In this example, “listening” is in present tense, “to be” is in the infinitive form, and “that you know how to have fun” is a sentence fragment. These items in the series do not match up.
  • Edited version: “Being a good friend involves listening, being considerate, and having fun.” In this example, “listening,” “being,” and “having” are all in the present continuous (-ing endings) tense. They are in parallel form.

Pronoun Reference/Agreement

  • Skim your paper, searching for pronouns.
  • Search for the noun that the pronoun replaces.
  • If you can't find any nouns, insert one beforehand or change the pronoun to a noun.
  • If you can find a noun, be sure it agrees in number and person with your pronoun.


  • Sam had three waffles for breakfast. He wasn’t hungry again until lunch.” Here, it is clear that Sam is the “he” referred to in the second sentence. Thus, the singular third person pronoun, “he,” matches with Sam.
  • Teresa and Ariel walked the dog. The dog bit her.” In this case, it is unclear who the dog bit because the pronoun, “her,” could refer to either Teresa or Ariel.
  • Teresa and Ariel walked the dog. Later, it bit them.” Here, the third person plural pronoun, “them,” matches the nouns that precede it. It’s clear that the dog bit both people.
  • “Teresa and Ariel walked the dog. Teresa unhooked the leash, and the dog bit her.” In these sentences, it is assumed that Teresa is the “her” in the second sentence because her name directly precedes the singular pronoun, “her.”


  • Skim your paper, stopping only at those words which end in "s." If the "s" is used to indicate possession, there should be an apostrophe, as in “Mary's book.”
  • Look over the contractions, like “you're” for “you are,” “it's” for “it is,” etc. Each of these should include an apostrophe.
  • Remember that apostrophes are not used to make words plural. When making a word plural, only an "s" is added, not an apostrophe and an "s."


  • It’s a good day for a walk.” This sentence is correct because “it’s” can be replaced with “it is.”
  • “A bird nests on that tree. See its eggs?” In this case, “its” is a pronoun describing the noun, “bird.” Because it is a pronoun, no apostrophe is needed.
  • “Classes are cancelled today” is a correct sentence whereas “Class’s are cancelled today” is incorrect because the plural form of class simply adds an “-es” to the end of the word.
  • Sandra’s markers don’t work.” Here, Sandra needs an apostrophe because the noun is a possessive one. The apostrophe tells the reader that Sandra owns the markers.