15 Grammar Mistakes That Ruin Even the Best Essays
Academic writing demands precision and clarity. Even brilliant ideas can lose their impact when undermined by grammar errors. This guide explores the 15 most common grammar mistakes that sabotage essays, providing practical solutions for students and professionals alike.
Common Grammar Errors That Undermine Your Writing
Grammar mistakes don’t just distract readers—they can fundamentally alter your meaning and damage your credibility. According to research from Stanford University, documents with grammar errors are perceived as less authoritative, regardless of content quality.
1. Subject-Verb Agreement Errors
Subject-verb agreement errors occur when the subject and verb don’t match in number. This mistake can confuse readers and make your writing appear careless.
Incorrect: The collection of books were displayed prominently. Correct: The collection of books was displayed prominently.
Remember that collective nouns (like “collection,” “group,” or “team”) typically take singular verbs, though exceptions exist in certain contexts.
2. Comma Splice Issues
A comma splice occurs when two independent clauses are connected with only a comma. This creates run-on sentences that compromise clarity.
Incorrect: The professor assigned the essay, it was due Friday. Correct: The professor assigned the essay; it was due Friday. Correct: The professor assigned the essay, and it was due Friday. Correct: The professor assigned the essay. It was due Friday.
According to Purdue University’s Online Writing Lab, comma splices rank among the top five grammar issues college instructors identify in student writing.
3. Misplaced and Dangling Modifiers
When modifiers aren’t properly positioned, they can create ambiguity or unintentionally humorous misinterpretations.
Dangling modifier: After running five miles, the paper was finally finished. (Who ran five miles? The paper?) Corrected: After running five miles, I finally finished the paper.
Misplaced modifier: The student wrote an essay about World War II in her pajamas. (Was the war fought in pajamas?) Corrected: In her pajamas, the student wrote an essay about World War II.
| Type of Modifier Error | Example | Correction |
|---|---|---|
| Dangling Modifier | Walking through the door, the room was empty. | Walking through the door, I found the room empty. |
| Misplaced Modifier | She almost read all the books. | She read almost all the books. |
| Squinting Modifier | Students who study regularly sometimes excel. | Students who study regularly will sometimes excel. OR Sometimes students who study regularly excel. |
4. Inconsistent Verb Tense
Shifting between past and present tense without reason confuses readers and disrupts the flow of your argument.
Incorrect: The author argues that climate change is serious, but then she went on to describe economic factors. Correct: The author argues that climate change is serious, but then she goes on to describe economic factors.
Dr. Elizabeth Johnson of Columbia University notes that inconsistent verb tense is particularly problematic in literature reviews and historical analyses.
5. Apostrophe Misuse
Apostrophes indicate possession or contraction—not plurality. Their misuse is immediately noticeable to educated readers.
Incorrect: The student’s submitted their essay’s late. Correct: The students submitted their essays late.
For possessives:
- Singular nouns: add ‘s (the student’s essay)
- Plural nouns ending in s: add ‘ (the students’ essays)
- Plural nouns not ending in s: add ‘s (the children’s toys)
Critical Punctuation Errors That Diminish Your Credibility
6. Semicolon Confusion
Semicolons connect related independent clauses or separate items in complex lists. Using them incorrectly suggests a poor understanding of sentence structure.
Incorrect: The professor gave feedback; because the essay needed revision. Correct: The professor gave feedback because the essay needed revision. Correct: The professor gave feedback; the essay needed revision.
7. Colon Misapplication
A colon introduces an explanation, list, or quotation that follows from the preceding clause. The clause before a colon should always be a complete sentence.
Incorrect: The main issues included: grammar, citation, and organization. Correct: The essay had three main issues: grammar, citation, and organization.
8. Run-on Sentences
Run-on sentences (including comma splices) overwhelm readers with too many ideas without proper punctuation.
Incorrect: The deadline approached quickly students panicked about their essays. Correct: The deadline approached quickly; students panicked about their essays. Correct: The deadline approached quickly, and students panicked about their essays. Correct: The deadline approached quickly. Students panicked about their essays.
According to research from Oxford University Press, essays with proper sentence boundaries score significantly higher in readability assessments.
Word Usage Pitfalls That Reveal Writing Immaturity
9. Pronoun-Antecedent Disagreement
Pronouns must agree with their antecedents in number, gender, and person. Disagreement creates confusion about what or whom you’re referring to.
Incorrect: Each student must submit their paper by Friday. (Traditional rule: “each” is singular) Correct: Each student must submit his or her paper by Friday. Also accepted in modern usage: Each student must submit their paper by Friday. (Now widely accepted as gender-neutral singular “they”)
| Traditional Approach | Modern Inclusive Approach |
|---|---|
| Each writer should revise his or her work. | Each writer should revise their work. |
| A doctor should always inform his patients. | Doctors should always inform their patients. OR A doctor should always inform their patients. |
10. Homophone Confusion
Homophones sound alike but have different meanings and spellings. Mixing them up immediately signals carelessness.
Common confusions:
- Their/They’re/There
- Their shows possession
- They’re is a contraction of “they are”
- There indicates location
- Your/You’re
- Your shows possession
- You’re is a contraction of “you are”
- Effect/Affect
- Effect is typically a noun meaning “result”
- Affect is typically a verb meaning “to influence”
Research from Cambridge University identifies homophone errors as one of the most common problems in undergraduate essays, occurring in nearly 40% of papers.
11. Sentence Fragments
Fragments lack either a subject, a complete verb, or both. They create a choppy, unprofessional impression.
Incorrect: Because the deadline was approaching. Correct: We worked quickly because the deadline was approaching. Stylistic fragment (acceptable in some contexts): The deadline. A source of endless stress.
Advanced Grammar Issues That Distinguish Excellent Writing
12. Faulty Parallelism
Parallelism requires using the same grammatical structure for elements in a series or comparison. Inconsistent structures disrupt the rhythm of your writing.
Incorrect: The professor emphasized citing sources, thorough research, and to proofread carefully. Correct: The professor emphasized citing sources, researching thoroughly, and proofreading carefully.
Dr. James Peterson, writing instructor at Princeton University, notes that “mastering parallelism transforms good writing into excellent writing.”
13. Split Infinitives
Although increasingly accepted, traditional grammar rules caution against placing words between “to” and a verb. Be aware of this convention while recognizing its evolution.
Traditional view (incorrect): She decided to carefully edit her essay. Traditional view (correct): She decided to edit her essay carefully.
Modern usage often accepts split infinitives, especially when avoiding them would create awkward phrasing.
14. Passive Voice Overuse
While not grammatically incorrect, excessive passive voice creates weak, indirect writing.
Passive: The essay was written by the student. Active: The student wrote the essay.
According to Harvard University’s Writing Center, active voice typically creates more engaging, concise prose. However, passive voice can be appropriate when:
- The actor is unknown or irrelevant
- You want to emphasize the recipient of an action
- You’re writing in scientific contexts where conventions favor passive voice
15. Vague Pronoun References
Pronouns without clear antecedents create ambiguity and force readers to work harder to understand your meaning.
Ambiguous: Jim discussed the essay with Tom, and he thought it needed revision. (Who thought? Jim or Tom?) Clear: Jim discussed the essay with Tom, who thought it needed revision.
| Common Pronoun Errors | Example | Correction |
|---|---|---|
| Ambiguous Reference | Maria told Sophia that she had won the award. | Maria told Sophia, “You have won the award.” |
| Missing Antecedent | They say essays should be double-spaced. | Professors say essays should be double-spaced. |
| Indefinite “This” | The essay had many grammar errors. This troubled the professor. | The essay had many grammar errors. This situation troubled the professor. |
FAQ: Common Grammar Questions
“Who” functions as a subject, while “whom” serves as an object. If you can substitute “he/she,” use “who”; if you can substitute “him/her,” use “whom.”
While traditionally discouraged, ending sentences with prepositions is increasingly accepted, especially when rewording would create awkward constructions. As Winston Churchill supposedly quipped, “This is the sort of nonsense up with which I will not put.”
Use “that” for essential/restrictive clauses (no commas needed) and “which” for non-essential/non-restrictive clauses (set off by commas).
While traditionally discouraged in formal academic writing, starting sentences with conjunctions is increasingly accepted for emphasis or stylistic reasons. However, use this technique sparingly in formal essays.
Use semicolons to join related independent clauses without a coordinating conjunction or to separate items in a list that already contains commas.