1. There/Their

One of the most common grammar mistakes is to mix up their and there. It's not that difficult to distinguish between the two! Here's an example to show the difference: Their books are over there. Their is a possessive. Some people also get confused by they're. That is a contraction of they are.

2. Must of/Should of

I must of done or I should of done are also used far too frequently. The correct form is should have. This mistake most likely comes about because have sounds rather like of when it's spoken. Make sure you get it right in written form.

3. …And Me

How often do you hear someone saying him and me went to the cinema? Neither pronoun is correct here. Take each one out of the sentence and you'll see how it should read. Him went or me went are clearly wrong. It should read He and I went to the cinema.

4. Your/You're

Your wrong! Yes, you most certainly are. It may be confusing that some words sound alike, but it shouldn't be that complicated to pick the correct one. Your is a possessive; you're is a contraction of you are.

5. Accept/except

The following text is found on many eBay sellers' pages: "I do not except responsibility in the case of a lost parcel". Leaving aside that eBay wouldn't agree with this statement, it should read "I do not ACCEPT responsibility". Funnily enough the confusion never seems to occur the other way round - you don't see I except all forms of payment.

6. It's/Its

Another common error is to write it's instead of its; for example, the baby was playing with it's toys. This mistake is probably down to the use of an apostrophe in possessives after names. When the mistake occurs in reverse (its going to rain), that's probably just lazy typing.

7. The Greengrocer's Apostrophe

This error is so named because it is often seen in shops selling fruits and vegetables. So you can buy potato's, tomato's and apple's. Potato's what, you may ask yourself? It's not just greengrocers though; I've seen ladie's, coffee's - and CD's often have an unnecessary apostrophe.

8. Double Negative

I never did nothing! Well, yes you did - you used a double negative, which does not exist in English (it does exist in other languages, for example Spanish). Double negatives cancel each other out - so you're actually implying that you did something … what was it?!

9. Fewer V Less

This is one that is less clear-cut. Should it be I had less clothes or fewer clothes? The answer is that it's fewer if it's a multiple of people or things. So you would say fewer clothes. If it can't be counted, then it's less. For example: I've had less free time since I started my new job.
Too many people think that correct grammar doesn't matter, but it helps create clarity if language is used correctly. It doesn't take much effort to work out which is the correct form to use. If you're not certain, pick up a grammar book or check one of the many style guides online. What is your pet hate among language errors?

SSC

9 Worst Grammar Mistakes