Some common grammar mistakes (and how to avoid them)

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French playwright, actor and poet Moliere is known to have once said, “Grammar which knows how to control even kings.” We couldn’t have said it better, because going through life without making a single grammar mistake is a tougher gig than wearing the crown.

If you’re in the business of writing, however, it’s not something that you can leave to chance, certainly not if you want your readers to take you seriously. Being careless with grammar will not impress the reader of your book, your academic supervisor, or shareholders reading your company annual report. It could get embarrassing, and you will lose credibility as a communicator or writer in the eyes of your target audience or readers, which could lead to poor book reviews, bad grades, or loss of sales.

Here’s a list of some common grammar mistakes that you can easily avoid:  

  1. There, their, or they’re?

There, their, and they’re are, of course, homophones: that is they have different meanings but sound the same. There refers to a place, they’re is a contraction of ‘they are’ and their indicates possession.  

Example: The car over there is their car, and they’re planning to sell it.

2. Affect versus effect

Referring to Merriam-Webster, ‘effect’ is a noun meaning ‘a change that results when something is done or happens,’ whereas ‘affect’ is usually a verb meaning ‘to act on or change someone or something’. This is usually the way the two words are used and remembering this will help you avoid mixing up the two most of the time. 

For example: 

  • The drought affected plant growth.
  • The second cup of coffee had no effect.

3. Then versus than 

One way to distinguish between the two is to remember that than is used when you’re talking about comparisons, while then is used when you’re talking about something relating to time. Think smaller than, larger than, more than, less than… whereas one would use then in phrases such as just then, back then, and every now and then.If you really want to get into the details, than is usually a conjunction used to connect nouns, verbs and adjectives, while then is usually used as an adverb

4. Who versus whom

Who is a pronoun, and whom is the objective case of who; that is it’s the form of who that is in the object position in a sentence. While you can usually get away with using who in the place of whom, if you are keen on understanding the difference, know that the tricky part is in determining the object position in a sentence.

One way to distinguish between the two is to remember that who, like other pronouns like ‘I’, ‘he’ and ‘she’, is a subject. So, it is the person performing the action of the verb. Whom, on the other hand, acts like ‘me’, ‘him’ and ‘her’ in a sentence. It is the object. That is, it is the person to/about/for whom the action is being done. 

So, a tip that usually works to help you pick the right word is: if you can replace the word with ‘he’ or ‘she’ or another subject pronoun, then use who. And if you can replace the word with ‘him’ or ‘her’ or another object pronoun, then use whom. You can remember this tip by associating the ‘m’ in him and whom. Neat, right!

Whom is also the correct choice after a preposition: use with whom, and one of whom, not ‘with who’ or ‘one of who’. 

5. Its versus it’s

It’s is a contraction of ‘it is’ or ‘it has’. For example: It’s raining heavily.

Its is a possessive form of the pronoun ‘it’, meaning belonging to ‘it’. For example: The system has its advantages.

An easy way to pick the right word is to replace the word with ‘it is’ or ‘it has’ in the sentence. If the resulting sentence is meaningful use it’s, if it’s not use it. It’s easy, isn’t it?

And never use an apostrophe after the s in its. That (its’) is just wrong!

6. Your versus you’re

Remember Ross explaining the difference between the two to Rachel in the sitcom Friends? Hilarious, and true! (Sorry Rachel.) 

You’re is a contraction of the phrase ‘you are’. Example: You’re going in the right direction.

Your is a possessive adjective used to show ownership. Example: I will be driving past your house this evening.

An easy tip to pick the right word is to replace the word with ‘you are’ in the sentence. If it makes sense, go with you’re, if not use your. Example: You’re clever at picking your battles.

Try the tip on these sentences:

  • Your hair looks soft and silky. 

You are hair looks soft and silky. Nah! Your is the right word here.

  • I appreciate your dancing skill.

I appreciate you are dancing skill. Nope. Your is the right word to use in this sentence.

  • You’re looking great today.

You are looking great today. Perfect! You’re sounds right here.

7. Less versus fewer

Less refers to quantities of things, while fewer refers to numbers of things. That is, less is used when the number is measured, whereas fewer is used when the number of things is counted. For example: fewer problems and less troubles.

The above is the most general rule, but there are exceptions. 

ABC offers the following explanation:

  • Fewer refers to numbers of things and is used with count nouns. Less refers to quantities of things and is generally used with mass nouns. So fewer jobs, but less employment.
  • Less is also used to modify units of time, money, measurement, and other general statistics. Example phrases: less than three miles, less than $50.
  • In special cases, mass nouns may become countable, making it permissible to use fewer. Example: The apothecary stocks fewer body butters than it used to.
  • Less is also used for some specific constructions: phrases such as five items or less, explain in 250 words or less
  • In speech or informal writing, less can be used before plural count nouns. For example: fewer jobs is an acceptable phrase.

So, you see that when you choose between less and fewer, sometimes you have to play it by ear. 

8. Everyday versus every day

Everyday (one word) is an adjective meaning ‘used or seen daily’ or ‘ordinary’, whereas every day (two words) is an adverb phrase meaning ‘daily’ or ‘every weekday’. Choosing between everyday and every day becomes easy when you imagine another word between ‘every’ and ‘day’ in the sentence. If the sentence is meaningful then use every day
For example, when you apply ‘single’ between ‘every’ and ‘day’ in the sentence ‘We watch the sunset together every day’, the sentence reads as ‘We watch the sunset together every single day. Makes sense. So, every day it is. 

9. Compliment versus complement

Compliment is an expression of esteem, approval, or admiration. Complement is related to completion. 


  • Everyone loves a compliment.
  • The headscarf complements her outfit.

10. Into versus in to

In to is not just into with a space in between. Into is a preposition that suggests movement of something toward or into something else. Example: Snowy walked into a lamp post because he wasn’t looking where he was going.

In to, on the other hand, is the adverb ‘in’ followed by the preposition ‘to’. Example: My manager insisted that I come in to work till the last day. 

One way to make the right choice is to remember that into answers the question ‘where’, while in to is the right choice if it can be replaced by ‘in order to’ in the sentence. 

Try it with the example sentences above.

We hope these tips and tricks will help you avoid some common grammatical mistakes. Or you could leave it to the experts. Visit the WordsRU website for proofreading services and get our editing experts to find the grammar mistakes and proofread your document. No sweat!