29 Common Grammar Mistakes: Examples and Corrections

Common grammar mistakes include subject–verb disagreement, sentence fragments, run-on sentences, incorrect verb forms, and missing articles. Punctuation and word-choice errors—such as misplaced apostrophes or confusing “its” with “it’s”—also belong on a proofreading checklist. Check the sentence’s structure first, then its individual words and punctuation.

This guide explains 29 issues using original examples from assignments, research notes, and student communication. It is a reference for edited academic English, not a ranking of error frequency. The examples illustrate language choices; they are not findings from real studies.

Use the explanations to check your own work or review suggestions from an online grammar checker. The aim is to understand the correction, not simply accept a different sentence.

Sentence structure mistakes

An independent clause can stand as a complete sentence. A dependent clause needs a main clause. That distinction helps with the first three checks; Purdue’s sentence-fragment guide provides further examples.

1. Leaving a sentence fragment on its own

Incomplete: Although the archive was closed.

Complete: Although the archive was closed, we could search its catalog online.

“Although” makes the first version depend on another clause. Add the missing main clause or remove “although” if you simply mean that the archive was closed. Headings and note fragments have different jobs from sentences in an essay.

2. Joining sentences without a boundary

Incorrect: The file was corrupted we restored the backup.

Correct: The file was corrupted. We restored the backup.

Both parts can stand alone. Separate them with a period, a suitable semicolon, or a conjunction with appropriate punctuation. A run-on is a problem with how clauses are joined, not a name for every long sentence.

3. Using a comma splice

Incorrect: The explanation is clear, the evidence is incomplete.

Correct: The explanation is clear, but the evidence is incomplete.

A comma alone does not normally join independent clauses in edited academic prose. A period or semicolon is another option. With “however,” write “The explanation is clear; however, the evidence is incomplete.” “However” does not function like the coordinating conjunction “but.”

4. Mixing grammatical patterns in a list

Inconsistent: The task involves locating sources, comparing findings, and to explain the differences.

Parallel: The task involves locating sources, comparing findings, and explaining the differences.

Keep equivalent items in matching forms. Here, all three activities use an -ing form. Purdue’s parallel-structure guidance also covers matching phrases and clauses, not just individual words.

5. Leaving a modifier without the right subject

Dangling: After reviewing the transcript, several contradictions became apparent.

Clear: After reviewing the transcript, I noticed several contradictions.

The contradictions did not review the transcript. Name the person who performed the action, or write “After I reviewed the transcript, several contradictions became apparent.” This is the connection to check when correcting a dangling modifier.

6. Placing a description beside the wrong noun

Unclear: We discussed the article in the seminar that challenged the original theory.

Clearer: In the seminar, we discussed the article that challenged the original theory.

The intended meaning is that the article challenged the theory. Moving the location phrase makes that connection clearer. This is a clarity correction: the original could describe a seminar that challenged the theory, so context determines the right revision.

Verb and agreement mistakes

Start by locating the subject and the complete verb phrase. Purdue’s agreement guide explains why a nearby plural noun does not necessarily require a plural verb.

7. Making the verb agree with the nearest noun

Incorrect: The explanation of these results require more detail.

Correct: The explanation of these results requires more detail.

“Explanation” is the singular subject; “results” belongs to the phrase describing it. Temporarily remove “of these results” to see the core sentence: “The explanation requires more detail.”

8. Giving “each” a plural verb

Incorrect: Each of the interview questions address a different topic.

Correct: Each of the interview questions addresses a different topic.

Here, “each” treats the questions individually and takes a singular verb. Compare “The interview questions address different topics,” where the subject is plural. Do not choose the verb solely from the noun immediately before it.

9. Changing tense without a change in time

Inconsistent: During yesterday’s session, we compared the plans and select a preferred option.

Consistent: During yesterday’s session, we compared the plans and selected a preferred option.

Both actions belong to the completed session. Tense changes are appropriate when the time changes: “We collected the responses yesterday and are analyzing them today.” Tense consistency does not mean putting an entire paper in one tense.

10. Using a past-tense form after “have”

Incorrect: I have wrote the methods section.

Correct: I have written the methods section.

Perfect verb forms use “have,” “has,” or “had” with a past participle. With irregular verbs, that form may differ from the simple past: “I wrote” but “I have written”; “we chose” but “we have chosen.” Check the particular verb rather than assuming every form ends in -ed.

11. Adding “-s” after a modal verb

Incorrect: This limitation might affects the conclusion.

Correct: This limitation might affect the conclusion.

Core modals such as “might,” “can,” and “should” take a following verb in its base form. Do not add an -s because the subject is singular. Cambridge’s modal-form guide explains the pattern, including combinations such as “might have affected.”

12. Choosing the wrong form after another verb

Incorrect: We avoided to repeat the same explanation.

Correct: We avoided repeating the same explanation.

“Avoid” normally takes an -ing form; “plan” takes a to-infinitive, as in “We plan to revise.” Other verbs allow both, sometimes with a different meaning. Check the specific verb pattern instead of applying one rule to every verb.

Pronouns, articles, and countability mistakes

These small words help readers identify who or what a sentence concerns. Article choice in particular depends on context; Cambridge’s guide to a, an, and the distinguishes a new or unidentified referent from one the reader can identify.

13. Using “I” where the sentence needs “me”

Incorrect: The tutor sent the comments to Ravi and I.

Correct: The tutor sent the comments to Ravi and me.

After “to,” the pronoun functions as an object. Remove the other name as a check: “to me,” not “to I.” As a subject, use “I”: “Ravi and I revised the outline.”

14. Leaving a pronoun’s reference unclear

Unclear: When the supervisor spoke to the researcher, she requested another draft.

Clearer: The supervisor requested another draft when she spoke to the researcher.

This revision assumes the supervisor made the request. If the researcher did, name the researcher instead. Both people could be “she” in the original. Clear pronoun reference is a meaning check, not an instruction to replace every pronoun with a name.

15. Choosing “a” or “an” from the letter rather than the sound

Incorrect: The application requires an university email address.

Correct: The application requires a university email address.

“University” begins with a consonant sound, despite its first letter. Compare “an hour,” where the initial sound is a vowel. Read the next word aloud when checking the article.

16. Omitting a determiner before a singular countable noun

Incorrect: The response needs clear example.

Correct: The response needs a clear example.

A singular countable noun used this way needs a determiner, such as an article, a possessive, or a demonstrative. “My example” and “this example” also work in suitable contexts. Plural and uncountable nouns follow different patterns.

17. Using “a” when you mean the same identified item

Unclear when referring to the same article: I downloaded a journal article. An article included an appendix.

Correct for the same article: I downloaded a journal article. The article included an appendix.

Use “the” to refer back to that identified article. If you mean a different, unidentified article, “an article” may be appropriate. A first mention can also take “the” when the reader already knows which item you mean; order of mention alone is not the rule.

18. Making an uncountable noun plural

Incorrect: The feedback contains several useful advices.

Correct: The feedback contains several useful pieces of advice.

“Advice,” “equipment,” and “information” are normally uncountable in these everyday academic uses. Count recommendations, pieces of equipment, or items of information instead. Cambridge’s countability reference separates these patterns by noun. Do not assume every English noun forms a plural by adding -s.

19. Mixing “fewer” and “less”

Preferred in edited academic English: This version has fewer headings and less repetition.

Use “fewer” for separate countable items and “less” for an uncountable amount. Cambridge notes that less with plural countable nouns occurs in informal speech, although edited usage generally favors “fewer.” Keep the register distinction instead of treating every conversational variation as a failure to understand English.

Apostrophe and comma mistakes

Punctuation can change how a sentence is read without changing its words. Use these checks alongside Purdue’s references on apostrophes and commas.

20. Adding an apostrophe to an ordinary plural

Incorrect: Three student’s submitted revised drafts.

Correct: Three students submitted revised drafts.

This sentence means more than one student; it does not express possession. Ordinary noun plurals do not need an apostrophe. “The student’s draft,” by contrast, refers to a draft associated with one student.

21. Putting a possessive apostrophe in the wrong place

Incorrect for several reviewers: The reviewers’s comments arrived today.

Correct: The reviewers’ comments arrived today.

A regular plural ending in -s takes an apostrophe after that ending. A singular noun usually takes ’s, as in “the reviewer’s comments.” An irregular plural without a final -s also takes ’s: “the children’s responses.” Work out the number of owners first.

22. Separating a subject from its verb with a comma

Incorrect: The final section of the literature review, needs revision.

Correct: The final section of the literature review needs revision.

A long subject does not require a comma before its verb. A genuine parenthetical interruption is different: “The final section, unlike the introduction, needs revision.” In that version, the two commas enclose an inserted phrase.

23. Changing a relative clause’s meaning with commas

For a particular subset: The essays that include source evaluations meet this requirement.

For all essays under discussion: The essays, which include source evaluations, meet this requirement.

The first identifies which essays qualify. The second presents the source evaluations as extra information about the essays already under discussion. Neither is automatically wrong; choose the intended meaning. Cambridge’s relative-clause guide also allows “which” in defining clauses, so do not treat every defining “which” as a grammatical error.

Commonly confused words

These are primarily word-choice and spelling distinctions, but they can be just as important as sentence structure when proofreading.

24. Confusing “its” and “it’s”

Incorrect: The chapter explains it’s central claim.

Correct: The chapter explains its central claim.

“Its” is possessive. “It’s” means “it is” or “it has.” Try expanding the contraction: “explains it is central claim” does not work. “It’s been revised” does work because it means “It has been revised.”

25. Confusing “your” and “you’re”

Incorrect: Your ready to submit the revised outline.

Correct: You’re ready to submit the revised outline.

“You’re” means “you are”; “your” marks possession, as in “your outline.” Expand the contraction when you are uncertain. Do not replace every instance automatically, because both forms may appear correctly in one sentence.

26. Confusing “their,” “there,” and “they’re”

Incorrect: Their presenting there findings tomorrow.

Correct: They’re presenting their findings tomorrow.

“They’re” means “they are,” while “their” marks possession. “There” can identify a location or introduce existence, as in “There are two appendices.” Check the job of each word rather than its sound.

27. Confusing “affect” and “effect”

Incorrect for influence: The revised wording may effect the interpretation.

Correct: The revised wording may affect the interpretation.

“Affect” commonly means influence; “effect” commonly names a result. Write “The revision had an effect on the interpretation.” These are not absolute verb-versus-noun rules: dictionaries also record the verb effect, meaning bring about, and the specialized noun affect.

28. Confusing “then” and “than”

Incorrect: The abstract is shorter then the introduction.

Correct: The abstract is shorter than the introduction.

“Than” introduces this comparison. “Then” can describe sequence: “Check the abstract, then review the introduction.” Decide whether the sentence compares things or describes an order of events.

29. Choosing an adjective where an adverb is needed

Incorrect: The presenter explained the procedure accurate.

Correct: The presenter explained the procedure accurately.

“Accurately” describes the action; “accurate” describes a noun, as in “an accurate explanation.” Not every adverb ends in -ly: “work hard” is correct. Cambridge’s adverb-form guide also explains why adjectives can follow linking verbs, as in “The explanation seems accurate.”

Do not turn style preferences into grammar rules

Passive voice can be correct. “The samples were labeled before storage” is a grammatical sentence. An active version may name a useful actor, but the passive may suit the passage’s focus. Cambridge’s passive-voice explanation describes that choice.

A final preposition is not automatically an error. “Which source are you referring to?” is a normal construction. “To which source are you referring?” is a more formal alternative. Cambridge explains the difference as preposition placement and register, not a requirement to repair every final preposition.

Context can justify a tense change. A paper may describe a completed procedure and discuss what its results mean now. Change a tense because the time reference is wrong, not merely because a neighboring sentence uses another tense.

Follow your course’s style guide and chosen variety of English where conventions differ. Label an optional rewrite as a preference; reserve “incorrect” for an actual problem in the stated context.

Practice: correct five sentences

Try these new examples before checking the answer key. Each sentence has one intended problem.

Answer key: “Each of the summaries contains a quotation”; “We avoided changing the question”; “The bibliography needs another check”; “The revised paragraph is clearer than the original”; “The chapter has lost its final page.”

To explain the answers, identify the subject in the first sentence, the form required after “avoid,” the subject–verb boundary, the comparison, and the possessive word. Correcting the word is useful; explaining why it changes gives you a test to use on your next draft.

How to check grammar mistakes with StudyPro

Use StudyPro’s Grammar & Style Checker on a draft whose meaning you understand. Its review workflow provides highlighted suggestions with explanations and options to apply, ignore, or undo changes. Check the current access limits before assuming every suggestion is included in a trial.

Read the explanation and then the whole sentence. Is the issue grammar, punctuation, clarity, or style? Does the proposed change retain the claim, terminology, and level of certainty? A sentence that changes “may suggest” to “proves” needs more than a language check.

Continue editing in Smart Editor, keeping the surrounding paragraphs in view. When you want alternative wording rather than a correction, AI Paraphraser serves a different task. For gaps in reasoning or organization, use Improvement Suggestions instead of assuming correct grammar makes the argument complete.

Keep a small record of errors you repeat: one example from your draft, its correction, and the rule you used. On the next assignment, check those patterns before running a broader review. Follow your assignment’s rules on automated editing, and do not silently change wording inside direct quotations.

Frequently asked questions

What are common grammar mistakes in essays?

Useful starting checks include agreement, sentence boundaries, verb forms, articles, pronoun references, apostrophes, and confused words. This list is not a universal frequency ranking. Use feedback on your own writing to decide which patterns need the most practice.

Are punctuation mistakes the same as grammar mistakes?

Not exactly. Grammar concerns how words and clauses are formed and combined; punctuation marks help organize written language. A comma splice involves both sentence structure and punctuation, so a proofreading guide often covers them together. Word-choice and style issues are separate again.

Can a grammar checker find every mistake?

Do not treat a report as a guarantee. Review suggestions against your intended meaning and the applicable conventions, especially for specialist terms, quotations, and context-dependent choices. Correct grammar does not establish that a statement is factual or that a reference supports it.

How do I avoid correcting sentences that are already acceptable?

Ask which rule the proposed change addresses. Check whether the issue is genuinely incorrect usage, unclear meaning, or a preference for a different tone. The examples above show why an article choice, a relative clause, or a passive sentence needs context before it can be judged.

Make the correction one you understand

Start with sentence structure and agreement, then review word forms, pronoun references, and punctuation. Keep useful terminology and accurate qualifications intact. A careful correction makes your meaning clearer without making the claim stronger than you intended.

Explore StudyPro’s Grammar & Style Checker for suggestions you can review in context. StudyPro is primarily paid with limited trial access; check the current plans and usage limits before reviewing a longer document.