---
title: "Common grammar mistakes"
url: https://erroneo.us/language/common-grammar-mistakes/
description: "The grammar mistakes that actually cost you credibility, from comma splices to 'between you and I', plus the fake rules you can safely ignore. With fixes."
type: guide
section: "Language"
date_modified: 2026-10-21
publisher: erroneo.us
license: All rights reserved. Quote with attribution and a link.
---

# Common grammar mistakes

> Ten errors worth fixing, each with a one-line repair, followed by four 'rules' you were probably taught that careful writers and dictionaries have long since abandoned.

Most grammar advice online mixes two very different things: real errors that make your writing harder to read, and old schoolroom superstitions that never reflected how good English works. This page separates them. The first section covers ten mistakes worth fixing. The second covers four "rules" you can retire with a clear conscience, along with the evidence.

## Ten grammar mistakes worth fixing

### 1. Comma splices

A comma splice glues two complete sentences together with nothing but a comma. The [Harvard Law School Writing Center](https://hls.harvard.edu/academics/hls-writes/writing-center/common-language-errors/) calls it the most common kind of run-on and offers three repairs: add a coordinating conjunction after the comma, swap the comma for a semicolon, or end the sentence.

Wrong: The launch went well~~,~~ traffic doubled overnight.

Right: The launch went well; traffic doubled overnight. *or* The launch went well, and traffic doubled overnight.

### 2. Subject–verb agreement across a long gap

Nobody writes *the dogs barks*. The trouble starts when a phrase separates the subject from its verb and the verb latches onto the nearest noun. Harvard's guide advises checking that the verb agrees with its actual subject, not the words in between.

Wrong: The list of approved vendors ~~are~~ on the shared drive.

Right: The list of approved vendors is on the shared drive.

Why: The subject is "list," not "vendors."

### 3. Apostrophes in plurals

The "greengrocer's apostrophe" (*apple's 50p*) is the single most visible punctuation error. [Purdue OWL](https://owl.purdue.edu/owl/general_writing/punctuation/apostrophe_introduction.html) is blunt: don't use apostrophes for noun plurals. It also says decades are written *the 1960s*, with no apostrophe before the s, and that capital letters and numbers don't need one to form a plural either.

Wrong: Fresh bagel~~'s~~ daily since the 1990~~'s~~.

Right: Fresh bagels daily since the 1990s.

### 4. It's vs its

Covered in depth on our [commonly confused words](https://erroneo.us/language/commonly-confused-words/) page, but it belongs on any grammar list. *It's* is only ever *it is* or *it has*; the possessive *its* takes no apostrophe ([Cambridge](https://dictionary.cambridge.org/grammar/british-grammar/it-s-or-its)).

### 5. "Between you and I"

After a preposition (*between, for, with, to*), pronouns take the object form: *me, him, her, us, them*. So it is *between you and me* and *a gift for my wife and me*. The wrong version is a textbook case of [hypercorrection](https://en.wikipedia.org/wiki/Hypercorrection): having been corrected for saying *you and me went* as children, people come to feel that *you and I* is always more proper. Rutgers English professor Jack Lynch described exactly this process in a [Voice of America interview](https://learningenglish.voanews.com/a/a-23-2007-07-23-voa3-83133807/117349.html).

>

**Quick test:** drop the other person. You would never say *a gift for I*, so *a gift for my wife and I* is wrong too.

### 6. Who vs whom

The traditional rule, as set out in the [American Heritage usage note](https://www.ahdictionary.com/word/search.html?q=who), is that *who* is a subject and *whom* is an object. The subtle part: when the pronoun is the subject of its own clause, it stays *who* even after a verb or preposition, as in *I know nothing about who supports the governor*. [Cambridge](https://dictionary.cambridge.org/grammar/british-grammar/who-whom) notes that *whom* belongs mainly to formal styles and writing, and its own examples show *who* standing in for it in ordinary use (*Anne Bolton, who he married*).

Wrong: The candidate ~~whom~~ we think is strongest withdrew.

Right: The candidate who we think is strongest withdrew.

Why: Strip out "we think": "the candidate who is strongest." It's the subject of "is."

### 7. Lay vs lie

*Lay* takes an object (you lay something down); *lie* does not (you lie down). The past tense of *lie* is *lay*, which is why this pair has been confused, per the [American Heritage Dictionary](https://www.ahdictionary.com/word/search.html?q=lay), since the 1300s. The dictionary's full set of correct forms:

| Verb | Present | Past | Past participle | -ing form |
|---|---|---|---|---|
| lie (recline) | I lie down | I lay down yesterday | it had lain there | I was lying in bed |
| lay (put) | lay the book here | he laid the newspaper down | the table was laid | she is laying tiles |

See also [Cambridge's lay or lie](https://dictionary.cambridge.org/grammar/british-grammar/lay-or-lie).

### 8. Fewer vs less

*Fewer* for countable things, *less* for mass amounts. The [American Heritage usage note](https://www.ahdictionary.com/word/search.html?q=less) also records that the supermarket sign *10 items or less* got a slightly warmer reception from its Usage Panel than other violations, though still not majority approval, and that *less than $400* and *less than three weeks* are standard.

### 9. "Could of" for "could have"

In speech, *could have* shrinks to *could've*, and the unstressed *'ve* sounds just like *of*. That's a normal feature of English [weak forms](https://en.wikipedia.org/wiki/Stress_and_vowel_reduction_in_English), but in writing it produces *could of, should of, would of*, which are always errors.

Wrong: You ~~should of~~ called first.

Right: You should have (or should've) called first.

### 10. Dangling modifiers

A dangling modifier describes someone who never actually appears in the sentence. [Purdue OWL](https://owl.purdue.edu/owl/general_writing/mechanics/dangling_modifiers_and_how_to_correct_them.html) recommends making the real doer the subject of the main clause, or rewriting the phrase as a full clause.

Wrong: Having arrived late for practice, ~~a written excuse was needed~~.

Right: Having arrived late for practice, the team captain needed a written excuse.

Why: Purdue's own example: the excuse didn't arrive late; the captain did.

## Four "rules" you can safely ignore

### Never end a sentence with a preposition

This one has a specific author. The [New Republic](https://newrepublic.com/article/113187/grumpy-grammarian-dangling-preposition-myth) traces it to a tossed-off criticism of Ben Jonson by the poet John Dryden in 1672, later cemented by 18th-century grammarians who admired Latin, which doesn't strand prepositions. Linguist Geoffrey Pullum's [notes on stranded prepositions](https://web.archive.org/web/20260102140857/http://www.lel.ed.ac.uk/~gpullum/SIEG/prepstranding.html) point out that Dryden gave no reason at all. *What are you looking at?* is perfect English; *At what are you looking?* is a costume.

### Never split an infinitive

*To boldly go* was fine all along. [Wikipedia's summary of the history](https://en.wikipedia.org/wiki/Split_infinitive) notes that prescriptivists campaigned against split infinitives from the 19th century, but recent usage guides have largely dropped the objection. Sometimes splitting is the only way to put the adverb where it belongs: *to more than double* has no graceful unsplit alternative.

### "Data" must be plural

Both uses are standard. The [American Heritage usage note](https://www.ahdictionary.com/word/search.html?q=data) says the plural survives mainly in scientific writing and that singular mass-noun *data* is standard for general audiences. It concludes it is "safe to say" singular *data* has become standard usage.

### "Hopefully" can't start a sentence

*Hopefully, the bill will pass* uses *hopefully* as a sentence adverb, just like *frankly* and *mercifully*. The [American Heritage usage note](https://www.ahdictionary.com/word/search.html?q=hopefully) observes that critics singled it out in the 1960s for no clear reason and that resistance has waned. If a reader you care about objects, *I hope* is always available.

## A proofreading checklist

- Search for every comma between two clauses and ask: could each side stand alone? If so, you have a splice.
- Find the verb, then find its real subject. Ignore the prepositional phrase in between.
- Search for `'s` and confirm each one is a possessive or a contraction, never a plural.
- Search for `and I` and try the drop-the-other-person test.
- Search for `of` after *could, should, would, might, must*.
- For each opening *-ing* phrase, check that the subject right after the comma is the one doing it.

Grammar errors cluster around the same handful of word pairs, so pair this page with [commonly confused words](https://erroneo.us/language/commonly-confused-words/) and [misused idioms and phrases](https://erroneo.us/language/misused-idioms-and-phrases/). If your argument is the problem rather than your sentences, see [logical fallacies](https://erroneo.us/thinking/logical-fallacies/).

## From the Error of the Day

1. Oct 21 Language[Comprised of: the phrase editors keep circling](https://erroneo.us/daily/comprised-of/) 'Is comprised of' is common but many editors still flag it. The whole comprises the parts; the parts compose the whole. Use 'comprises' or 'consists of'.

## Frequently asked questions

**Can you end a sentence with a preposition?**

Yes. The supposed rule traces back to a remark by the poet John Dryden in 1672, and linguists such as Geoffrey Pullum have shown that stranded prepositions are normal English used by great writers for centuries. Rewrite only if the sentence reads awkwardly.

**Is it 'between you and me' or 'between you and I'?**

Between you and me . Between is a preposition, and the pronoun after a preposition takes the object form (me, him, her, us, them). Between you and I is a classic hypercorrection.

**What is a comma splice?**

Two complete sentences joined only by a comma: The court intended to broaden standing, it did not clarify the limits . Fix it with a conjunction ( , but ), a semicolon, or a full stop.

**Is 'data' singular or plural?**

Both are standard. The American Heritage Dictionary notes that plural data remains common in science, while singular mass-noun data (like information ) is standard in general writing; in its 2005 survey 66 percent of its Usage Panel accepted Once the data is in, we can begin to analyze it .

**Is it wrong to split an infinitive?**

No. Prescriptivists objected from the 19th century onward, but recent usage guides have largely dropped the objection. To boldly go is fine; move the adverb only if the result reads better.

## Sources

1. [Harvard Law School Writing Center: Common language errors](https://hls.harvard.edu/academics/hls-writes/writing-center/common-language-errors/)
2. [Purdue OWL: Apostrophe introduction](https://owl.purdue.edu/owl/general_writing/punctuation/apostrophe_introduction.html)
3. [Purdue OWL: Dangling modifiers and how to correct them](https://owl.purdue.edu/owl/general_writing/mechanics/dangling_modifiers_and_how_to_correct_them.html)
4. [Cambridge Dictionary: It's or its?](https://dictionary.cambridge.org/grammar/british-grammar/it-s-or-its)
5. [Wikipedia: Hypercorrection](https://en.wikipedia.org/wiki/Hypercorrection)
6. [VOA Learning English: Wordmaster on hypercorrection](https://learningenglish.voanews.com/a/a-23-2007-07-23-voa3-83133807/117349.html)
7. [American Heritage Dictionary: usage note at 'who'](https://www.ahdictionary.com/word/search.html?q=who)
8. [Cambridge Dictionary: Who, whom](https://dictionary.cambridge.org/grammar/british-grammar/who-whom)
9. [American Heritage Dictionary: usage note at 'lay'](https://www.ahdictionary.com/word/search.html?q=lay)
10. [Cambridge Dictionary: Lay or lie?](https://dictionary.cambridge.org/grammar/british-grammar/lay-or-lie)
11. [American Heritage Dictionary: usage note at 'less'](https://www.ahdictionary.com/word/search.html?q=less)
12. [Wikipedia: Stress and vowel reduction in English (weak forms)](https://en.wikipedia.org/wiki/Stress_and_vowel_reduction_in_English)
13. [Geoffrey K. Pullum: Stranded prepositions (archived)](https://web.archive.org/web/20260102140857/http://www.lel.ed.ac.uk/~gpullum/SIEG/prepstranding.html)
14. [The New Republic: The dangling preposition myth](https://newrepublic.com/article/113187/grumpy-grammarian-dangling-preposition-myth)
15. [Wikipedia: Split infinitive](https://en.wikipedia.org/wiki/Split_infinitive)
16. [American Heritage Dictionary: usage note at 'data'](https://www.ahdictionary.com/word/search.html?q=data)
17. [American Heritage Dictionary: usage note at 'hopefully'](https://www.ahdictionary.com/word/search.html?q=hopefully)

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