5 Most Common English Grammar Mistakes

 In Learn English

These common English grammar mistakes are made by both native speakers and English language learners.  As a non-native speaker, you may well have seen signage, heard English news presenters or actors or read English language online content that contains a few of these common English grammar mistakes. Here, we list these mistakes, then provide the grammatical rules and examples of incorrect and correct use of these  mistakes.  Native speakers and English learners both can attain perfect English grammar with this useful guide to English grammar in use.

Common Grammar Mistakes and How to Correct Them

  1. Who/whom … that

The rules: “Who” refers to the subject of a sentence; “whom” refers to the object.

How to use each word: Correct usage is guaranteed if you associate the word “who” with “she’, and ‘whom’ with “her”.  You will then know which word to use by framing them as questions, i.e.: Who did this? She did” – so “who” is correct. “Whom should we ask? Ask her” – so “whom” is correct.

Note, never use “that” instead of “who” or “whom”. When referring to a person, you should not use the word “that”.

Whom shall I call? Who shall I call?
Who is attending? Whom is attending?
Sheila is the person who did that. Sheila is the person that did that.


  1. Affect/effect

Common Grammar Mistakes in EnglishThe rules: Affect is a verb – “to affect” – meaning to influence or have an impact on something. Effect is a noun – “a positive effect” – referring to the result of being affected by something.

There is also a verb “to effect”, meaning to bring something about – “to effect a change” but it’s not part of common  English usage so we will focus on affect and effect

Painting the room pink has a pretty effect Painting the room pink has a pretty affect
The fires affected both people and animals The fires effected both people and animals


  1. I.e. and e.g.

These two abbreviations are commonly confused. but they mean very different things.

The rules: I.e. means “that is” or “in other words”. E.g. means “for example”. It comes from the Latin words “exempli gratia”.

Write these abbreviations as “i.e.” and “e.g.” only when writing informally. In formal documents, write out the meanings (“for example” or “that is”).

She loves all citrus e.g. oranges, tangerines, grapefruit She loves all citrus i.e. oranges, tangerines, grapefruit
He hates the cold – i.e. he’s not coming to Alaska He hates the cold – e.g. he’s not coming to Alaska


  1. Misplaced apostrophes

Incorrect placement of apostrophes is one of the most common grammar mistakes in the English language. Understanding the rules is all you need to use apostrophes correctly.

The rules: Apostrophes show possession. To show that something belongs to one person, place the apostrophe before the ‘s’. For instance, “The dog’s bowl.” To show that something belongs to more than one person, place the apostrophe after the ‘s’. For example, “The dogs’ bowl.”

Apostrophes are also used to contract two adjoining words, replacing a missing letter. For example, “don’t” has apostrophe where the “o” from “do not” should be.

Note: apostrophes are never used to make a word, even in number form, plural.

The cats are in the tree The cat’s are in the tree
Books for the library Book’s for the library
In the 1900s In the 1900’s
The girls’ dresses are ready for them to collect The girls dresses are ready for them to collect
Jane’s horse is over there Janes horse is over there


  1. Could/would/should of

Because the contracted form of “could have” – “could’ve” – sounds like “could of” when spoken, this common mistake of replacing “have” with “of” is occurs when they follow  “should” and “would”.

The rules: Could, would and should – we can use “should” to apply to the three words: “Should’ve” and “Should have” are both correct; the latter is more formal. “Should of” in written form, has not meaning and is grammatically incorrect. What the writer means is  “should have”. The shortened version of “should have” is “should’ve”.

We could’ve saved some money there today We could of saved some money there today
I would have filled up with gas then I would of filled up with gas then
You should’ve told me this You should of told me this


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