Q:

Is it really OK to use "because of"?

I recently learned from a YouTube video that "because of" is not correct. But my friend argues that "because of" is actually correct. Also, I see a lot of people writing and saying "because of". Here's a example:

That's because of you.

So, is it actually correct to use "because of" or only new learners think it's correct or is it not correct at all?

A:

Actually, 'of' can be correct, in standard grammar, after because. It depends on what comes after that.
If the next part is a complete and potentially free-standing clause (say, a verb phrase), then you don't need (or want) of:

That's because I'm smart.
  I'm hungry because I haven't eaten.
  You're only saying that because I'm pretty.
  I'm wet because it's raining.

But if the bit after it is a noun phrase, you need the of:

That's because of my asthma.
  I'm angry because of your tone.
  I'm happy because of you.
  You're only saying that because of my looks.

You will also run into a lot of non-standard usage in some places using the of even where it isn't used in standard grammar.

A:

Both because and because of are correct in different contexts.

Because is used by itself when the cause is expressed as a clause:  

He opened his umbrella because it was raining.

Because is used with of when the cause is expressed as a noun or nominal:

He opened his umbrella because of the rain. 

However, there is a fairly new hip usage which drops of; often it also drops determiners on the nominal representing the cause, casting the cause as a 'generic': 

He opened his umbrella because rain.

This usage is quite widespread, but not yet ready for formal registers. In her admirable article "English Has a New Preposition, Because Internet" Megan Garber describes it as "exceptionally bloggy and aggressively casual and implicitly ironic".

