Because and because of

Because is a conjunction. It is used at the beginning of a clause.

She was depressed because she didn’t know what to do.

She won the first prize because she worked hard.

Note that because and its clause can go after or before the main clause.

Because she worked hard she won the first prize. OR She won the first prize because she worked hard.

Because of is a two-word preposition. It is used before a noun or pronoun.

Compare:

The match was cancelled because it rained.

The match was cancelled because of the rain. (NOT The match was cancelled because the rain.)

She won the first prize because she worked hard.

She won the first prize because of her hard work. (NOT She won the first prize because of she worked hard.)

Grammar notes

Because-clauses cannot usually stand alone.

He did not come to school because he was ill. (NOT He did not come to school. Because he was ill.)

However, in answers because-clauses can stand alone.

‘Why are you crying?’ ‘Because John hit me.’