因为 two or more reasons. and difference with 是因为

Question

I was going to write the following sentence and have two doubts:

他去看医生，因为他自己觉得身体很弱，学习时思想不能集中。

1. I wanted to say: "He went to the doctor because she was feeling weak and could not concentrate when studying". Is it correct to put only one 因为 or do i have to put one for feeling weak and another for the other clause for not concentrating in his studies?

2. Could I use the clause 是因为 instead of 因为? Are them both correct? Is there any difference? When is it better to use each one?

他去看医生，是因为他自己觉得身体很弱，学习时思想不能集中。

Answer 1

do i have to put one for feeling weak and another for the other clause for not concentrating in his studies?.

No, I think a coordinating conjunction is fine enough, same as you did in your English translation:

因为他自己觉得身体很弱，（并且 / 而且 / 且 / 还有）学习时思想不能集中

Could I use the clause 是因为 instead of 因为? are both correct? is there any difference? When is it better to use each one?

Yes you could use 是因为 here, and it would be correct, and yes there would be a difference, not in meaning but in what part of the sentence you are stressing.

By saying 他去看医生，是因为 you are implying that the focus of the sentence is going to the doctor, and that this requires an explanation. Compare with English: "Why does he go to the doctor? It's because he feels weak".

Whereas by saying 因为 you are implying that the focus of the sentence is the cause itself, which results in going to the doctor. Compare with English: "He feels weak, so he goes see the doctor".

As an additional remark, according to Chinese topic-comment grammar rules, this latter case where you put emphasis on the cause would require to invert the sentences:

因为他自己觉得身体很弱，（所以）他去看医生

Answer 2

I wanted to say: "He went to the doctor because she was feeling weak and could not concentrate when studying". Is it correct to put only one 因为 or do i have to put one for feeling weak and another for the other clause for not concentrating in his studies?

It is correct to use one 因为. Using two will be strange. But you can use “还因为” for the other clause, or "不但因为" "而且因为" for two clauses to make it natural.

Could I use the clause 是因为 instead of 因为? Are them both correct? Is there any difference? When is it better to use each one?

Yes you can. Both are correct. No difference. Here I think both are equally good. Usually they are interchangeable.

Answer 3

因爲 is not an essential word.

他去看医生，他自己觉得身体很弱，学习时思想不能集中。 is totally correct.

When you want to emphasize the reason, add it by your need.

他去看医生，因爲他自己觉得身体很弱，学习时思想不能集中。

But you can't add 2 因爲 here, because "weak then can't concentrate" is ONE cause.

You can add 是因爲, but you need to remove the comma.

他去看医生是因爲他自己觉得身体很弱，学习时思想不能集中。

And 是因爲 make the sentence explicitly past tense. The tense of the original is ambiguous.

If you do have multiple reasons, you want to have a strong emotional sense, you can add more 因爲.

他去看医生了, 因爲他自己觉得身体很弱，因爲周圍的人認爲他有病, 因爲他的父母强迫他去。

This structure, 3 or more similar structures or phrases follow each other is a rhetoric method -- 排比, which can deliver a strong impact.