The twenty most common errors in college writing were identified by Andrea Lunsford and Robert Connors in research examining thousands of student essays in the late 1980s. Explanations of the errors have been adapted from The Everyday Writer by Lunsford and Connors (New York: St. Martin’s Press, 1997, pages 11-14).

1. Missing comma after an introductory element
Many sentences begin with one or more introductory elements—clauses, phrases, or single words that lead into the main body of the sentence. To show where an introductory element ends and the main part of the sentence begins (thus helping your readers move more easily through the sentence), insert a comma after the introductory element. If the sentence includes multiple introductory elements, use a comma after each one.

Incorrect: Collectively the cashew usually ranks as the third or fourth greatest nut of commerce (by mass) worldwide.

Correct:   Collectively, the cashew usually ranks as the third or fourth greatest nut of commerce (by mass) worldwide.

2. Vague pronoun reference
Readers should be able to easily identify a pronoun’s antecedent (that is, the specific word or phrase to which the pronoun refers). If the antecedent is unclear (either because there is more than one possible pronoun reference or because the word to which the pronoun refers is implied but not actually stated in the text), you need to make the reference more explicit.

Incorrect: The rurally situated processing plants purchase nuts from local farmers and provide employment for villagers. They represent a local, diffuse cash infusion.

Correct:   The rurally situated processing plants purchase nuts from local farmers and provide employment for villagers. These processing plants represent a local, diffuse cash infusion.

3. Missing comma in a compound sentence
When two independent clauses (clauses that can stand alone as separate sentences) are joined by a coordinating conjunction such as and, but, so, yet, nor, or for, precede the conjunction with a comma to signal a pause between the two parts of the sentence. The pause gives pace to the sentence and helps prevent sentence misreadings. In the following example, the sentence contains three independent clauses.

Incorrect: A number of other pests cause minor disfigurement of leaves and fruit but these pests do not seriously affect nut production so they are usually ignored by owners.

Correct:   A number of other pests cause minor disfigurement of leaves and fruits, but these pests do not seriously affect nut production, so they are usually ignored by owners.

Note: Be sure to distinguish between compound sentences, as defined above, and sentences that have two or more predicate phrases but only one subject. Sentences with a compound predicate do not take a comma between the two parts of the predicate. For example:

Incorrect: These pests disfigure leaves and fruit, but don’t affect nut production.

Correct:   These pests disfigure leaves and fruit but don’t affect nut production.

4. Wrong word
Most instances of this error arise from confusion or carelessness regarding homonyms or other words that either sound similar or have similar meanings. Wrong-word errors may also result from overly casual use of a thesaurus.( Be sure to consult a dictionary if you’re not sure of the exact meaning of a word you find in a thesaurus.)

Incorrect: Are interest in cashew began in 1985 with the observation that both single and small groups of cashew trees nationalized around the Calicut district of Kerala, India, were visited by forging ants, spiders, and wasps.

Correct:   Our interest in cashew began in 1985 with the observation that both single and small groups of cashew trees naturalized around the Calicut district of Kerala, India, were visited by foraging ants, spiders, and wasps.

5. Missing comma(s) with a non-restrictive element
Non-restrictive elements are words, phrases, and clauses that provide relevant information in a sentence but are not essential to the sentence’s basic meaning. Non-restrictive elements in a sentence should be set off (on both sides) with commas. In the following example, the non-restrictive element is underlined.

Incorrect: The trees which produced a crop of nuts and inflated pedicles harvested by local residents showed no evidence of herbivory, and there were no Homoptera present.

Correct:   The trees, which produced a crop of nuts and inflated pedicles harvested by local residents, showed no evidence of herbivory, and there were no Homoptera present.

6. Wrong or missing verb ending (-s or –es, -d or –ed)
In spoken English, we sometimes either omit verb endings altogether or pronounce them inaudibly, but standard written English requires their use even when other information in the sentence implies these endings. Make sure that subject and verb agree (plural or singular) and that you are using the correct verb tense. (See also #10.)

Incorrect: Of course, it’s important to stay inform about the pest problems that can occur when cashew is grown in commercial-size monoculture plantings.

Correct:   Of course, it’s important to stay informed about the pest problems that can occur when cashew is grown in commercial-size monoculture plantings.

7. Wrong or missing prepositions
A sentence’s meaning may change depending on the preposition you use in conjunction with a verb or as part of a prepositional phrase. For example, the act of comparing something to something else involves looking for similarities among the two items; the act of comparing something with something else means registering both similarities and differences between the items. The acts of meeting at or in an intersection have different implications, as do the acts of talking around, about, or through an issue.

Incorrect: The insect helopeltis spp. is endemic of and drives insecticide usage through Southeast Asia, India, and East Africa.

Correct:   The insect helopeltis spp. is endemic to and drives insecticide usage throughout Southeast Asia, India, and East Africa.

8. Comma splice
Inexperienced writers sometimes combine two or more independent clauses (clauses that are capable of standing independently as separate sentences) into a single sentence by inserting a comma between the clauses. This error can be corrected in several ways: by separating the clauses into stand-alone sentences; by replacing the comma with a semicolon; by following the comma with a coordinating conjunction such as and, but, so, yet, nor, or for; or by rewriting the sentence to subordinate or eliminate one of the independent clauses.

Incorrect: Numerous studies have shown that ants can interfere with herbivores, Bentley now addresses the general context of ants as potential biocontrol agents in agriculture.

Correct:   Numerous studies have shown that ants can interfere with herbivores. Bentley now addresses the general context of ants as potential biocontrol agents in agriculture.
or
Numerous studies have shown that ants can interfere with herbivores; Bentley now addresses the general context of ants as potential biocontrol agents in agriculture.
or
Numerous studies have shown that ants can interfere with herbivores, and Bentley now addresses the general context of ants as potential biocontrol agents in agriculture.
or
While numerous studies have shown that ants can interfere with herbivores, Bentley now addresses the general context of ants as potential biocontrol agents in agriculture.

9. Missing or misplaced possessive apostrophe
Possessive nouns (nouns that indicate possession of something else) generally have an apostrophe-s ending if singular (e.g. botanist’s or Davis’s) or just an apostrophe if plural (e.g. botanists’ or Davises’). Possessive personal pronouns (hers, his, ours, theirs, yours, its), however, do not take apostrophes.

Incorrect: Observation of the ant’s activity over a 3-wk period revealed that 5 different ant species were visiting extrafloral nectaries.

Correct:   Observation of the ants’ activity over a 3-wk period revealed that 5 different ant species were visiting extrafloral nectaries.

10. Unnecessary shift in tense
Unless you have a clear reason for doing otherwise, use the same tense for all verbs both within and across sentences.

Incorrect: An inflorescence develops from the axillary bud of a left-like bract, and during its development and elongation it lay flat near the bract adaxial surface.

Correct:   An inflorescence develops from the axillary bud of a left-like bract, and during its development and elongation it lies flat near the bract adaxial surface.

11. Unnecessary shift in pronoun
When you use a pronoun reference in a sentence, make sure that you use the same pronoun for all subsequent references in the sentence. The most common example of pronoun shifting is the shift between one and I, you, or we.

Incorrect: One might consider the presence of any kind of ant on a crop plant potentially dangerous because of the insect’s often-seen ability to tend coccids or aphids, but perhaps we should think this matter through more carefully.

Correct:   One might consider the presence of any kind of ant on a crop plant potentially dangerous because of the insect’s often-seen ability to tend coccids or aphids, but perhaps one should think this matter through more carefully.

12. Sentence fragment
A sentence fragment is an incomplete portion of a sentence that is punctuated as a full sentence. To correct this error, incorporate the fragment into the preceding or subsequent sentence, or rewrite the fragment to include subject and predicate. In some types of writing (for example, in fiction and journalistic writing), authors may incorporate fragments as a stylistic choice. In academic writing, however, the use of fragments is far less common.

Incorrect: We made an interesting and unexpected discovery. Great variations in the amount and type of ground cover for any given age class of trees.

Correct:   We made the interesting and unexpected discovery that the amount and type of ground cover for any given age class of trees varies greatly.
or
We made an interesting and unexpected discovery. We learned that the amount and type of ground cover for any given age class of trees varies greatly.

13. Wrong tense or verb form
A verb must clearly show when a condition or action is, was, or will be completed.

Incorrect: The stages of fruit development have included one in which ants were attracted to a specific region of the developing nut.

Correct:   The stages of fruit development include one in which ants are attracted to a specific region of the developing nut.

14. Lack of subject–verb agreement
The verb form used in a sentence may vary depending on whether the subject is singular or plural and whether the sentence is written in first-, second-, or third person. When you are looking for subject–verb agreement errors, be mindful that the noun closest to the verb may not be the subject.

Incorrect: One of our purposes in doing this study have been to find evidence that a diverse assemblage of natural predators can replace chemical pesticides.

Correct:   One of our purposes in doing this study has been to find evidence that a diverse assemblage of natural predators can replace chemical pesticides.

When the subject consists of two or more nouns connected by and, the subject is generally plural. However, when all parts of the subject refer to the same thing or person, the subject is considered singular (see the second example following).

Correct:   The principal investigator and her associates are interested in finding evidence that a diverse assemblage of natural predators can replace chemical pesticides.

Correct:   Our principal purpose and intent throughout this study has been to find evidence that a diverse assemblage of natural predators can replace chemical pesticides.

When the subject consists of two or more nouns connected by or or nor, verb agreement should be with the subject noun that is closest to the verb.

Correct:   Neither the principal investigator nor her associates believe that chemical pesticides are the only solution to this problem.

15. Missing comma in a series
To avoid potential sentence misreadings, always insert a comma between the last two items in a three-or-more-item list.

Incorrect: Cashew nut trees are consistently ant-visited throughout the year, with the ants attracted to a large number of extrafloral nectaries on the leaves, inflorescences, flowers and developing nuts.

Correct:   Cashew nut trees are consistently ant-visited throughout the year, with the ants attracted to a large number of extrafloral nectaries on the leaves, inflorescences, flowers, and developing nuts.

16. Lack of agreement between pronoun and antecedent
When you use a pronoun (such as you, him, she, their, it) in place of the noun to which it refers (called the pronoun’s antecedent), make sure the pronoun agrees with its antecedent in both gender and number.

Incorrect: The ants methodically fed at a number of nectaries before descending the branch/trunk system and returning to its nest.

Correct:   The ants methodically fed at a number of nectaries before descending the branch/trunk system and returning to their nests.

Note that modifiers like each, every, one, and (in some cases) either and neither are singular, and so the nouns they modify will require singular pronoun references. Also, singular noun antecedents joined by or or nor require a singular pronoun.

Incorrect: Each ant methodically fed at a number of nectaries before descending the branch/trunk system and returning to their nests.

Correct:   Each ant methodically fed at a number of nectaries before descending the branch/trunk system and returning to its nest.

Some noun antecedents (for example, “botanist” or “researcher”) are non-gender-specific; that is, they may refer to both males and females. When you use this type of antecedent in its singular form, your pronoun references to the antecedent must acknowledge both genders. You have several options for establishing pronoun agreement with non-gender-specific nouns: (1) For every pronoun reference, use “him and her, “she and he,” etc. Some writers find this awkward and choose instead to alternate between male and female pronoun references either paragraph by paragraph or section by section. (2) You can change the sentence wording to make the antecedent (and therefore the pronoun) plural. (3) You can simply get rid of the pronoun. All three solutions are illustrated here.

Incorrect: Every aspiring botanist should cultivate his laboratory and field research skills.

Correct:   Every aspiring botanist should cultivate her or his laboratory and field research skills.
or
All aspiring botanists should cultivate their laboratory and field research skills.
or
Every aspiring botanist should cultivate laboratory and field research skills.

17. Unnecessary comma(s) with a restrictive element
Restrictive elements are essential to the basic meaning of the sentence. They should not be set off from the rest of the sentence through the use of commas. In the following example, intended meaning is not that all researchers were consulted but rather that those researchers with whom we did consult arrived at their estimates in this fashion.

Incorrect: The researchers, with whom we consulted, arrived at their estimates of ground ant diversity and abundance by continuously censusing a bait trapline.

Correct:   The researchers with whom we consulted arrived at their estimates of ground ant diversity and abundance by continuously censusing a bait trapline

18. Fused sentence
Fused, or run-on, sentences occur when clauses that could stand alone are joined with no linking words or punctuation. Correct this error in one of four ways: (1) Separate the clauses into two (or more) sentences; (2) insert a semicolon between the clauses; (3) insert a comma followed by a coordinating conjunction (e.g. and, but, so, yet, nor, for) between the clauses; or (4) rewrite the sentence to subordinate or eliminate one of the independent clauses.

Incorrect: Yield from these plantations was considered satisfactory growers continue to be interested in pest protection and the cost of doing business, however.

Correct:   Yield from these plantations was considered satisfactory. Growers continue to be interested in pest protection and the cost of doing business, however.
or
Yield from these plantations was considered satisfactory; however, growers continue to be interested in pest protection and the cost of doing business.
or
Yield from these plantations was considered satisfactory, but growers continue to be interested in pest protection and the cost of doing business.
or
Although yield from these plantations was considered satisfactory, growers continue to be interested in pest protection and the cost of doing business.

19. Misplaced or dangling modifier
To prevent sentence misreadings, place modifying words and phrases as close as possible to the word or words they modify.

Incorrect: These plantings demonstrate that a pesticide-free, income-producing cashew crop can be successfully grown within areas where government agriculturists consider pesticides an absolute necessity on a pure cost basis.

Correct:   These plantings demonstrate that on a pure cost basis, a pesticide-free, income-producing cashew crop can be successfully grown within areas where government agriculturists consider pesticides an absolute necessity.

20. Its/It’s confusion
Its indicates possession; it’s is a contracted form of it is.

Incorrect: The relationship with ants is not an incidental or trivial event, however, and—if its to lead to elimination of pesticide use in cashew production—it demands more detailed study.

Correct:   The relationship with ants is not an incidental or trivial event, however, and—if it’s to lead to elimination of pesticide use in cashew production—it demands more detailed study.

Most of these sample sentences were adapted from Fred R. Rickson and Melinda P. Rickson’s 1998 article on “The Cashew Nut, Anacardium Occidentale (Anacardiaceae), and its Perennial Association with Ants: Extrafloral Nectary Location and the Potential for Ant Defense,” in the American Journal of Botany, vol. 85, no. 6, pp. 835-849. Handout prepared by Beth Russell, Oregon State University, 1998, and revised by Tracy Ann Robinson. With thanks to Dr. Don Armstrong, OSU Department of Botany and Plant Pathology, for his content review.