The most common grammar mistakes are mixing up words that sound alike (their, there, they're), verbs that do not agree with their subject, missing or wrong articles, switching tense in the middle of a story, and comma splices that join two sentences with a comma. Each has a quick test you can learn in a minute, and a free grammar checker catches them all in one pass.
Below are 15 mistakes with a wrong and a right example, the test that tells them apart, and a simple way to check a whole email or essay before you send it.
Which grammar mistakes are the most common?
Most errors in everyday writing come from a short list: sound-alike words, subject and verb agreement, articles, verb tense, apostrophes and punctuation between sentences. They are easy to make when typing fast and easy to miss when rereading your own words, because your brain reads what you meant to write.
1 to 5: Words that sound alike
| Mistake | Wrong | Right | Quick test |
|---|---|---|---|
| their / there / they're | Their going home. | They're going home. | Can you say "they are"? Use they're. |
| your / you're | Your welcome. | You're welcome. | Can you say "you are"? Use you're. |
| its / it's | The company changed it's logo. | The company changed its logo. | It's always means "it is" or "it has". |
| then / than | She is taller then me. | She is taller than me. | Comparing? Use than. Time order? Use then. |
| affect / effect | The rain will effect the match. | The rain will affect the match. | Affect is usually the verb, effect the noun. |
6 to 8: Verbs that do not match
6. Subject and verb agreement. A singular subject takes a singular verb, even when other words sit between them.
- Wrong: The list of names are on the desk.
- Right: The list of names is on the desk. (The subject is "list", not "names".)
7. Switching tense. Pick past or present for a story and stay with it.
- Wrong: She walked in and sits down.
- Right: She walked in and sat down.
8. Wrong verb form after "did" or "to". The verb after them stays in its base form.
- Wrong: Did you went to the meeting?
- Right: Did you go to the meeting?
9 and 10: Articles and plurals
9. Missing or wrong articles. Use "a" before a consonant sound and "an" before a vowel sound, and do not drop the article before a singular countable noun.
- Wrong: I need a advice. She is engineer.
- Right: I need some advice. She is an engineer. ("Advice" is uncountable, so it takes "some", not "a".)
10. Plurals after numbers and "every". Numbers above one take a plural noun; "every" takes a singular one.
- Wrong: She goes to school every days. It costs five dollar.
- Right: She goes to school every day. It costs five dollars.
11 to 13: Punctuation between and inside sentences
11. Comma splice. Two full sentences need a full stop, a semicolon or a joining word, not just a comma.
- Wrong: The file is ready, I will send it now.
- Right: The file is ready, so I will send it now. or The file is ready. I will send it now.
12. Apostrophes in plurals. Plurals do not take an apostrophe; possessives do.
- Wrong: We sell apple's and orange's.
- Right: We sell apples and oranges. (But: the apple's skin.)
13. Missing comma after an introductory phrase. A comma after a longer opening phrase makes the sentence easier to read.
- Wrong: After the meeting ended we went home.
- Right: After the meeting ended, we went home.
14 and 15: Capitals and confused pairs
14. Capital letters. Capitalise the first word of a sentence, names, days, months, languages and "I".
- Wrong: i met sarah on monday to practise english.
- Right: I met Sarah on Monday to practise English.
15. Fewer or less. Use fewer for things you can count and less for amounts.
- Wrong: Less people came this year.
- Right: Fewer people came this year. (But: less water, less time.)
Three sentence-level mistakes to watch
These are about how a sentence is built rather than single words, so reread for them yourself as well:
- Sentence fragments. A group of words without a full clause is not a sentence. Because the server was down. needs the rest: We lost an hour because the server was down.
- Dangling modifiers. The opening phrase must describe the subject that follows it. Walking to work, the rain started. says the rain walked; write Walking to work, I got caught in the rain.
- Lists that do not match. Items in a list share the same form. She likes hiking, to swim and reading. becomes She likes hiking, swimming and reading.
How do you check grammar quickly and for free?
Paste your text into a grammar checker, read the highlighted changes and accept the result. The WoowTools grammar checker fixes grammar, spelling, punctuation and capitalization in one click, with no account, and explains every change so you learn from it.
- Paste or type up to 5,000 characters into the box.
- Click Check grammar and wait a few seconds.
- Read your text with the changes highlighted: removed words in red, new words in green.
- Scroll to What was fixed for a short reason next to each correction, such as "verb tense" or "singular noun".
- Switch to Clean text and copy the corrected version.
For example, She go to school every days and dont like it. comes back as She goes to school every day and doesn't like it., with three fixes listed: verb tense, singular noun and contraction.
The checker makes the smallest changes needed and keeps your meaning, tone, names and formatting. It works in many languages, including English, Spanish, French, Portuguese, Russian, Hindi, Arabic and Chinese, and answers in the language you wrote in. Your text goes over an encrypted connection to our own AI server, is checked once and is not stored.
Grammar checker or proofreading by hand?
Use both: let the checker catch the slips, then reread for meaning. A checker is fast and reliable for the mistakes in this list, but it cannot know what you meant to say, whether a fact is right or whether the tone suits the reader.
| Job | Grammar checker | Rereading yourself |
|---|---|---|
| Typos and sound-alike words | Very good | Easy to miss in your own text |
| Agreement, tense, articles | Very good | Good if you read slowly |
| Punctuation between sentences | Good | Good |
| Whether the message is clear | Limited | Essential |
| Facts, names and numbers | Cannot check | Essential |
Two habits help when you reread: read the text aloud, and read it from the last sentence to the first, which stops you skimming.
Tips for fewer grammar mistakes
- Write first, fix later. Checking while drafting slows you down; run the check once the text is done.
- Keep sentences short. Most agreement errors and comma splices hide in long sentences.
- Learn your personal top three. If the checker keeps fixing the same mistake, learn its quick test from the table above.
- Watch the word count. For essays and forms with a limit, check the length in the word counter after correcting.
- Fix headings separately. Title capitals follow their own rules; the case converter turns a heading into Title Case or sentence case.
Check your text now
Paste your email, essay or post into the free grammar checker, read the highlighted fixes and copy the corrected version. It takes a few seconds and catches every mistake on this list.
Frequently asked questions
What are the most common grammar mistakes?
Sound-alike words such as their, there and they're, subject and verb agreement, missing articles, switching tense, and comma splices. They make up most errors in everyday emails and essays.
How can I check my grammar for free?
Paste your text into a free grammar checker such as the WoowTools grammar checker. It highlights each change, explains why it was made and needs no account.
What is a comma splice?
A comma splice joins two complete sentences with only a comma, as in 'The file is ready, I will send it now.' Fix it with a full stop, a semicolon or a joining word such as 'so'.
Does a grammar checker fix punctuation?
Yes. It corrects punctuation and capitalization along with grammar and spelling. It cannot judge whether your meaning is clear, so reread the text once after checking.
Is it fewer or less?
Use fewer for things you can count, such as fewer people or fewer emails, and less for amounts, such as less water or less time.
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