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: While most people regard ecology as the study of pollution and conservation the science is in fact far more diverse.

Correct:   While most people regard ecology as the study of pollution and conservation, the science is in fact far more diverse.

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: In tropical rain forests, some species are deprived of light. This results in overgrowth competition.

Correct:   In tropical rain forests, some species are deprived of light. This deprivation results in overgrowth competition.

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.

Incorrect: Local ecologists are concerned about the rate at which plant and animal resources are diminishing in this area and they have launched a campaign to increase public awareness of this issue.

Correct:   Local ecologists are concerned about the rate at which plant and animal resources are diminishing in this area, and they have launched a campaign to increase public awareness of this issue.

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: Local ecologists are concerned about the area’s diminishing plant and animal resources, and are recommending land-use policy changes.

Correct:   Local ecologists are concerned about the area’s diminishing plant and animal resources and are recommending land-use policy changes.

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: The main affect of seasonality on vegetation in the tropics is that leaves are generally shed quickly and replaced in the dry season.

Correct:   The main effect of seasonality on vegetation in the tropics is that leaves are generally shed quickly and replaced in the dry season.

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 (a phrase modifying heterosis) is underlined.

Incorrect: The opposite of heterosis or outbreeding is inbreeding.

Correct:   The opposite of heterosis, or outbreeding, is inbreeding.

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: The distribution patterns of many species are limit by global temperatures.

Correct:   The distribution patterns of many species are limited by global temperatures.

Incorrect: Global temperatures limits many species’ distribution patterns.

Correct:   Global temperatures limit many species’ distribution patterns.

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: We compared the communities within the biome with one another to identify their common traits.

Correct:   We compared the communities within the biome to one another to identify their common traits.

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: (1) by separating the clauses into stand-alone sentences; (2) by replacing the comma with a semicolon; (3) by following the comma with a coordinating conjunction such as and, but, so, yet, nor, or for; or (4) by rewriting the sentence to subordinate or eliminate one of the independent clauses.

Incorrect: Occupying nearly three-quarters of the Earth’s surface, marine environments are among the most extensive on this planet, they are also among the most uniform.

Correct:   Occupying nearly three-quarters of the Earth’s surface, marine environments are among the most extensive on this planet. They are also among the most uniform.
or
Occupying nearly three-quarters of the Earth’s surface, marine environments are among the most extensive on this planet; they are also among the most uniform.
or
Occupying nearly three-quarters of the Earth’s surface, marine environments are among the most extensive on this planet, and they are also among the most uniform.
or
Occupying nearly three-quarters of the Earth’s surface, marine environments are among the most extensive and uniform on this planet.

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

Incorrect: Ecologists expressed concern that the species habitat would soon be destroyed.

Correct:   Ecologists expressed concern that the species’ habitat would soon be destroyed.

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: The amount of carbon dioxide in the atmosphere may increase considerably when volcanoes erupted.

Correct:   The amount of carbon dioxide in the atmosphere may increase considerably when volcanoes erupt.

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: Often, when one embarks on the study of ecology, you feel overwhelmed by the diversity of material.

Correct:   Often, when one embarks on the study of ecology, one feels overwhelmed by the diversity of material.

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: Abiotic factors are conditions of the physical world in which biotic organisms live. Factors such as temperature, moisture, light, soil PH and nutrient content, salinity, and water current velocity.

Correct:   Abiotic factors, such as temperature, moisture, light, soil PH and nutrient content, salinity, and water current velocity, are conditions of the physical world in which biotic organisms live.
or
Abiotic factors are conditions of the physical world in which biotic organisms live. Such factors include temperature, moisture, light, soil PH and nutrient content, salinity, and water current velocity.

13. Wrong tense or verb form
The verbs in a sentence must clearly communicate whether the condition or action being reported in the sentence is happening in the past, present, or future, whether the action is definite or conditional, and so on. Be on the alert for irregular verbs (verbs that don’t follow the standard pattern for indicating tense) that have been treated as regular verbs.

Incorrect: Our knowledge of genetics came a long way since Darwin’s theory of evolution.

Correct:   Our knowledge of genetics has come a long way since Darwin’s theory of evolution.

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: The physical structure of desert plants are linked to water conservation and heat load.

Correct:   The physical structure of desert plants is linked to water conservation and heat load.

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:   Water conservation and heat load requirements factor into the physical structure of desert plants.

Correct:   The agency’s chief ecologist and acting director has effected many policy changes during the past nine months.

In the case of subject parts joined by or or nor, agreement should be with the part closest to the verb.

Correct:   Neither its heat load capacity nor its water requirements mark it as a likely candidate for desert cultivation.

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: Animals that use chemical defense include the bombadier beetle, the skunk and the octopus.

Correct:   Animals that use chemical defense include the bombadier beetle, the skunk, and the octopus.

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: All species within a given ecological community has its own niche.

Correct:   All species within a given ecological community have their own niche.

Note that the words each, every, one, and (often) either and neither are singular and therefore require singular pronoun references. Also, singular noun antecedents joined by or or nor require a singular pronoun.

Incorrect: Within a given ecological community, each species has their own niche.

Correct:   Within a given ecological community, each species has its own niche.

Some noun antecedents (for example, “ecologist” 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, 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: An ecologist generally spends a portion of his work week in the field.

Correct:   An ecologist generally spends a portion of his or her work week in the field.
or
Ecologists generally spend a portion of their work week in the field.
or
An ecologist generally spends a portion of the work week in the field.

17. Unnecessary comma(s) with a restrictive element
Restrictive elements are words, phrases, and clauses that are essential to the basic meaning of the sentence. Do not set restrictive elements apart from the rest of the sentence with commas. In the following example, the intended message is not that all ecologists are following the debate over wildlife preserve design but rather that those who are interested in this debate will find the island biogeography theory useful.

Incorrect: Ecologists, who are following the debate over design of wildlife preserves, will find the island biogeography theory particularly useful.

Correct:   Ecologists who are following the debate over the design of wildlife preserves will find the island biogeography theory particularly useful.

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: Sedentary cultivation represents the permanent manipulation of an ecosystem the biota are removed and replaced with domesticated plants and animals.

Correct:   Sedentary cultivation represents the permanent manipulation of an ecosystem. In this approach, the biota are removed and replaced with domesticated plants and animals.
or
Sedentary cultivation represents the permanent manipulation of an ecosystem; this approach replaces the biota with domesticated plants and animals.
or
Sedentary cultivation represents the permanent manipulation of an ecosystem, for this approach removes the biota and replaces them with domesticated plants and animals.
or
Sedentary cultivation, an approach that removes the biota and replaces them with domesticated plants and animals, represents the permanent manipulation of an ecosystem.

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: The marine ecologists could see the whales spouting and diving with binoculars.

Correct:   With binoculars, the marine ecologists could see the whales spouting and diving.

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

Incorrect: Each different biome has it’s own type of floral and faunal assemblage.

Correct:   Each different biome has its own type of floral and faunal assemblage.

Many of these sample sentences were adapted from Peter Stiling’s Ecology: Theories and Applications, 3rd ed. (Englewood Cliffs, NJ: Prentice Hall, 1999). Handout prepared by J. Rinterknecht, Oregon State University, 1998, and revised by Tracy Ann Robinson. With thanks to Dr. Kate Lajtha, OSU Department of Botany and Plant Pathology, for her content review.