Which word(s) can be used to express causal relation in modern English? [closed]

I will skip it over, because nobody will have doubt on this.

Since nobody will have doubt on this, I will skip it over.

I will skip it over, for nobody will have doubt on this.

An American friend told me that we should avoid using “for” or “since” when describing a causal relation.

Is this true? I feel that these three sentence have no differences at all.

Solution 1:

because, since, after, for, as and of can all express causation, with because being the strongest, most explicit single word doing so. All can be used correctly; you were probably told to use because based on the explicit causation of the word.

He died because he had cancer.
Since his cancer had left him immunocompromised, he died.
He died after his cancer metastasized to his brain.
He died, for his cancer had metastasized to his brain. (formal and out of general use)
As he had no immunity following chemotherapy, he died.
He died of an overwhelming infection.

As the word becomes weaker, sentence structure must become stronger to show causation, so, if not paying attention, it is probably a good thing to remember that because will not fail you. Having said that, all of your sentences show causation, for you have constructed them well.

Solution 2:

Your examples (with corrections irrelevant to your point):

I will skip over it, because nobody will have any doubts about this.

Since nobody will have any doubts about this, I will skip over it.

I will skip over it, for nobody will have any doubts about this.

are all grammatical. The first two are perfectly idiomatic; the third one, with for is a little bit literary or old-fashioned.

[Another point unrelated to your question: in the first and third, it would probably be best to swap it and this, so that it refers back, as it does in the middle one].