Because must be followed by a subject and a verb. Therefore, if the subject of both clauses is the same, we have to repeat the subject or the subject pronoun after "because".
Because is a subordinating conjunction and must be followed by a subject and a verb in English. Therefore, if the subject of both clauses is the same, we should repeat the subject after because. For example:
I went to the doctor because was experiencing back pain.
I went to the doctor because I was experiencing back pain.
By contrast, because of is a preposition and should be followed by a noun (or a noun phrase). Therefore, "because of" is not followed by the subject of a sentence.
I went to the doctor because of I was experiencing back pain.
I went to the doctor because of my back pain.
1. How to Avoid Repeating the Same Subject Pronoun
Repeating the subject pronoun after because is correct and considered perfectly fine. In many situations, however, you can avoid reiteration by using these techniques:
- replacing the pronoun by a noun, or
- sentence transformation.
Replacing the Pronoun by a Noun
Frequently, you can use a name, family relationship, work relationship, etc. to avoid repeating the same subject pronoun. For example:
- Rebecca didn't go to school because she felt sick.
- Your sister is a top writer because she has a natural talent.
- My boss is happy because he has been promoted to general manager.
- My friend passed the test because he worked hard.
In many situations, you can change the form of your sentence without changing its meaning. This is called sentence transformation.
Look at these examples:
- I didn't do it because I misunderstood what he said.
- I didn't do it because of a misunderstanding.
We can avoid subject repetition by:
- replacing because by the preposition because of, and
- using a noun ("misunderstanding" in the example above) instead of a verb ("misunderstood" in the first sentence).
- He went to the dentist because he was experiencing a toothache.
- He went to the dentist because of a toothache.
- She asked for a loan because she was facing financial difficulties.
- She asked for a loan because of her financial difficulties.
2. Starting a Sentence with Because
The same rules apply if we start our sentence with because or because of:
- Because is followed by a subject and a verb.
- Because of should be followed by a noun or a noun phrase.
If we start a sentence with because, we place a comma after the first clause. For example:
Because she was angry she started shouting at me.
Because she was angry, she started shouting at me.
- Because I was hungry, I ordered a pizza over the phone.
- Because of my appetite, I ordered a pizza over the phone.
3. More Examples with 'Because' and 'Because of'
- The company didn't hire more employees because it was faced with a financial crisis.
- Because he was thinking about his new girlfriend, my brother couldn't stay focused while studying.
- She didn't call me because she was working until late hours in the evening.
- Because he wanted to maintain weight loss over time, he started exercising.
- We cancelled the event because of the rain,
- We arrived late because of the flight delay.
- Because of the distance, they took a train.
- She got distracted because of the noise.
You can follow this strategy before deciding whether to use the same subject after because:
- If you are using the preposition because of, add a noun or a noun phrase after it.
- If you are using the subordinating conjunction because, place the subject in the second clause and pay attention to the use of commas:
- Place a comma after the first clause if the sentence starts with because.
- Don't add a comma if the sentence starts with the main clause. There are a few exceptions where you can use a comma before "because". Most of the time, however, you won't need it.
You can learn more about subject repetition about coordinating conjunctions on our post about repeating the subject after "but".