Common Spelling / Grammar Mistakes

I’m a strong believer in the power of language.
If you can express yourself clearly and coherently you are more likely to avoid problems and misunderstandings.
It’s also a lot easier to communicate with people when there is less ambiguity.

Unfortunately a LOT of people seem to have serious issues with spelling. I think we all make mistakes from time to time and confuse words a little, but the more common mistakes I’m talking about are really annoying and when I come across them in documents or on websites (or in emails) it really annoys me.

Here are a few:

its vs it’s

“its” denotes possession. For example:
Ireland is an island. Its capital city is Dublin.

“it’s” is short for either “it is” or “it has”. For example:
It’s a nice day.

Simple rule of thumb. If you can replace the apostrophe with “is” or “has” and the sentence still makes sense then you know you’re using it correctly (I hope!)

your vs. you’re

Same as above. “your” denotes possession, while “you’re” is the contraction of “you are”

whether vs weather. Do I really need to explain that one?

their vs they’re vs there
“their” denotes possession. eg. Their car was blue.
“they’re” is the contraction of “they are” eg. They are Italian.
“there” denotes position.

There are some cases where the spelling is different depending on the words usage ie. the difference between the verb and the noun.

One example of this would be:
effect vs affect
Effect is the noun, while affect is the verb.

There are probably quite a few other common ones, so if you know of any please feel free to add them in the comments.

Thanks to the guys and girls on Twitter last night for sharing some of the examples.

And to @lecraic for this hilarious explanation of spelling mistakes