'because' versus 'because of'

because

• It is a conjunction/connector which is used to introduce a cause or reason
• Therefore, it is used at the beginning of a clause, before a subject + verb (VERB PHRASE)
• It connects subordinating clauses to the main clause of a sentence (refer to previous post on clauses)  

Examples:  

                  Zhi Ming went to bed because he was tired.

                  We were late because it was raining.

                  Fandi was absent in school for two days because he caught a flu.

                 *Note that the subordinate 'because' clause can go after or before the main clause

Other acceptable examples:

                  Because he was tired, Zhi Ming went to bed 

                  Because it was raining, we were late.

                  Because he caught a flu, Fandi was absent in school for two days.

because of

• It means on account of; by reason of
• It is a two-word preposition, and NOT a conjunction
• Therefore, it is used before a NOUN or PRONOUN (NOUN PHRASE)

Examples:  

                  Zhi Ming went to bed because of his tiredness.

                  We were late because of the rain.

                  Fandi was absent in school for two days because of a flu he caught.

Take a quiz to test your understanding of the difference between 'because' and 'because of' here. Can you get all 17 questions correct? :)