"Because" introduces a full clause with subject and verb; "because of" is followed by a noun or pronoun.
Conjunction. Joins two clauses. What follows "because" is always a full clause: subject + verb + complements.
She was late because the traffic was terrible.
Ella llego tarde porque el trafico estaba terrible.
He could not sleep because he was too nervous.
El no pudo dormir porque estaba muy nervioso.
I chose this career because I love helping people.
Escogi esta carrera porque me encanta ayudar a la gente.
Compound preposition. Followed by a noun, pronoun, or noun phrase. Cannot introduce a clause with a conjugated verb.
She was late because of the traffic.
Ella llego tarde por el trafico.
The game was canceled because of the rain.
El partido fue cancelado por la lluvia.
He could not sleep because of his nerves.
El no pudo dormir por sus nervios.
Common mistake
Very common error: "She was late because of the traffic was terrible." Wrong. "Because of" cannot precede a clause with a verb. Correct: "because the traffic was terrible" (conjunction + clause) or "because of the traffic" (preposition + noun). Simple test: if what follows has a conjugated verb, use "because". If only a noun, use "because of".
Trick to remember it
Look at what comes after: is there a conjugated verb? Use "because". Is there only a noun or pronoun? Use "because of". Because + [subject + verb]. Because of + [noun].
Quick rule
Because + clause (subject + verb). Because of + noun.
Did you know?
"Due to" and "owing to" are synonyms of "because of": always followed by a noun. "Due to the rain, the game was canceled." In formal English, "due to" is often preferred. "Since" and "as" are synonyms of "because" (with a clause): "Since it was raining, we stayed inside." They are more formal and less emphatic.
Exercise 1 · Pick the right one
The flight was delayed _____ a technical problem with the aircraft.
Exercise 2 · Pick the right one
I could not concentrate _____ my neighbor was playing loud music.
Exercise 3 · Form the word
Because + clause (subject + verb). Because of + noun.
Very common error: "She was late because of the traffic was terrible." Wrong. "Because of" cannot precede a clause with a verb. Correct: "because the traffic was terrible" (conjunction + clause) or "because of the traffic" (preposition + noun). Simple test: if what follows has a conjugated verb, use "because". If only a noun, use "because of".
Look at what comes after: is there a conjugated verb? Use "because". Is there only a noun or pronoun? Use "because of". Because + [subject + verb]. Because of + [noun].
Bryan López
Founder of SpeakUP Academy