You reread your draft and still sense something is off. The most common grammar mistakes are fragments, comma splices, agreement slips and look-alike words such as its and it’s, and each has a quick fix.
If you want the wider picture first, start with our guide to writing and language basics.
| Item | Value |
|---|---|
| Mistakes in GrammarBook’s 2024 list | 10 mistakes |
| Ways to fix a comma splice (Swansea University) | 3 options: full stop, coordinating conjunction or semicolon |
| Parts a complete sentence needs | 2 parts: a subject and a predicate |
| Lay and lie | 2 verbs: lay takes an object, lie does not |
These figures come from GrammarBook’s 2024 newsletter and Swansea University’s Academic Skills Lab. Lists and guidance can change, so check the sources before you rely on them.
Why do the same common grammar mistakes keep coming back?
Many slips start in speech. Conversational habits can spill into writing, and some errors never show when you talk. Homophone mistakes, for example, will not affect speech but stain writing, because the ear cannot hear the spelling.
Verb endings are another case. Endings such as -s, -es and -ed are sometimes forgotten because they are not always pronounced. You read what you meant to write, not what is on the page.
The fix is to name the error, not just correct it once. When a mistake keeps reappearing, Blinn College’s writing guidance says it should be addressed specifically. Keep a short list of your own repeat offenders and check for them on every draft.
The rest of this guide groups the usual suspects into four families:
- Sentence-level errors: fragments, comma splices, run-ons and dangling modifiers.
- Agreement and pronoun errors.
- Word-choice errors, including homophones and malformed verb phrases.
- Punctuation slips, mainly apostrophes and commas.
Sentence-level mistakes: fragments, comma splices and run-ons
A sentence fragment is an incomplete sentence. According to Swansea University, a complete sentence needs a subject and a predicate, and the predicate must hold a finite verb. “While the second result was positive.” leaves the reader waiting, so finish the thought: “While the second result was positive, the rest were inconclusive.”
A run-on sentence joins two independent clauses with no punctuation or linking word between them. A comma splice joins them with a comma alone. The Swansea guide gives the same cure for both: a full stop, a coordinating conjunction such as “and”, or a semicolon.
Here is a comma splice and its repairs:
- Splice: The grass is getting long, you should mow it soon.
- Full stop: The grass is getting long. You should mow it soon.
- Conjunction: The grass is getting long, so you should mow it soon.
- Semicolon: The grass is getting long; you should mow it soon.
Swansea offers a handy test: if you can use a full stop in that spot, it is the wrong place for a comma.
A dangling modifier describes the wrong element in the sentence. GrammarBook’s advice is to place a modifier as close as possible to the element it modifies. “Walking to the station, the rain soaked her coat” makes the rain the walker; “Walking to the station, she got her coat soaked by the rain” fixes it.
Agreement and pronoun mistakes
In subject-verb agreement, a singular subject takes a singular verb and a plural subject takes a plural verb, as GrammarBook puts it. The trap is the phrase that sits between the two. In “The box of old books have been in the attic”, the subject is box, so the verb should be has.
Collective nouns trip people up in the same way. GrammarBook treats “The audience is applauding the performance” as the correct form. Pick the verb that matches the single group, then stay consistent.
Pronouns cause their own trouble. Watch for these three:
- Subject versus object: correct grammar places subject pronouns in subject positions and object pronouns in object positions, so write “with Jerrod and me” and “Ravi and I would like”.
- Vague reference: pronouns must clearly refer to a specific word, so replace a loose “this” or “it” with the noun it stands for.
- Agreement with the antecedent: “The team changed its strategy” keeps the pronoun matched to a single group.
The pronoun and vague-reference points are backed by Blinn College’s handout.
Word-choice mistakes: homophones and look-alikes
Homophones sound the same but differ in spelling and meaning. The classic pairs are its and it’s, your and you’re, and there, their and they’re. Slow down on these when you proofread, because a spell checker will not flag a correctly spelled wrong word.
For its and it’s, QuillBot’s guide suggests reading the sentence with “it is”. If that makes sense, write it’s; if not, write its. Blinn College’s handout adds that its is possessive and it’s is a contraction of it is or it has.
Other pairs and phrases worth memorising:
- Than versus then: use “than” when you are comparing, and “then” for time or consequence.
- Affect versus effect: La Trobe University’s library guide says affect is usually a verb meaning to impact, and effect is usually a noun meaning a result.
- Would of, must of: these are incorrect, so write “would have” and “must have”.
- Lay versus lie: lay takes an object, while lie does not. The scarf is lying on the bin; Barry laid the shovel in the yard.
- Adverb versus adjective: “dances well” and “working really hard”, not “dances good” or “working real hard”.
The e.g. and i.e. pair is also worth a note. GrammarBook says i.e. restates something (“in other words”) and e.g. introduces examples (“for example”). Use e.g. before a list of examples and i.e. before a rewording.
Punctuation slips: apostrophes and commas
For apostrophes, Blinn College’s rule is to use ‘s for singular nouns and plural nouns not ending in -s, and only an apostrophe for plural nouns ending in -s. That gives “a child’s well-being”, “children’s costumes” and “the Yankees’ pitcher”. Possessive pronouns such as its never take an apostrophe.
Commas cause two opposite problems. Some writers leave them out where they belong, for instance after an introductory word, phrase or clause. Others add them where they do not belong, such as before “because”.
- Add a comma after an introductory element: “After the meeting ended, we left.”
- Skip the comma before “because”, “when” or “if” when they begin a dependent clause: QuillBot’s guide notes that you need a comma only before a coordinating conjunction in a compound sentence.
- Do not use a comma alone to join independent clauses; that is the comma splice from earlier.
Passive voice is not an error, but QuillBot says that overusing it can lead to wordiness. Reserve it for moments when you want to emphasise the thing acted upon, as in “My neighbour was stung by a bee”.
A simple proofreading routine
Knowing the rules is half the job; the other half is catching slips in your own text. La Trobe University’s guide urges you to proofread thoroughly for sentence-level errors. A repeatable routine works better than a single quick skim.
- Let the draft rest, then read it aloud so fragments and run-ons are easier to hear.
- Check each sentence for a subject and a finite verb, and for a match in number between them.
- Scan for the homophones and look-alikes you personally mix up.
- Check every apostrophe and every comma against the rules above.
- Keep a log of corrections, so your repeat errors become visible.
The same habits help in every genre. If you are reviewing fiction or non-fiction, our guide on how to write a book review shows where clean sentences matter most. For first-person writing, how to write a personal essay covers voice, where deliberate sentence fragments are a style choice rather than a slip.
Frequently asked questions
What are the most common grammar mistakes?
Show answer
Sources agree on a core set: run-on sentences and comma splices, subject-verb agreement errors, homophone mix-ups such as its and it’s, misplaced apostrophes and sentence fragments. GrammarBook’s 2024 list of 10 also includes dangling modifiers, lay and lie, and e.g. versus i.e.
How do I fix a comma splice?
Show answer
Replace the comma with a full stop, add a coordinating conjunction after it, or switch to a semicolon, as Swansea University’s guide describes. If a full stop would fit in that spot, the comma is wrong.
Is “its” or “it’s” correct?
Show answer
Use its for possession and it’s only when you mean it is or it has. Read the sentence with “it is” in place; if it still makes sense, the apostrophe belongs.
Is it ever fine to start a sentence with a fragment?
Show answer
The sources treat fragments as errors in academic and formal writing. Some writers use them on purpose for effect in creative work, but make sure it is a choice and not an accident.
