It's been a few years since I took grammar writing, so I'm kinda rusty with my comma skills. I know that one of the comma rules is that two independent clauses must be joined with a comma, however, it feels weird to put one in the following sentence.

Traditional monotherapy (single-drug treatment) with chemotherapeutic agents is an ineffective treatment for tumors because cancer cells are extremely diverse in their metastatic ability.

Is this correct, or does there need to be a comma before "because"? Thanks in advance!

  • Why would there be a comma before a regular use of because?
    – Lambie
    Mar 19, 2018 at 23:29

2 Answers 2


Your rule is correct; but those aren't "two independent clauses". The clause because cancer cells are extremely diverse in their metastatic ability is dependent/subordinate, as it cannot stand on its own.

The rules for subordinate clauses are more complex and less definite. In the case of subordinate conjunctions, like because, I believe most style guides allow but do not prescribe the comma, depending on context. If the subordinate clause is felt to be very closely connected to the main clause, and/or if it is very short, style guides would probably advise that you leave out the comma; if not, then write a comma. This advice is of course somewhat vague; it leaves considerable freedom to authors.

In your example, I find it hard to judge the 'closeness' of the connection between the clauses. I would say it could go either way. The subordinate clause is not short, however, which would weigh in favour of a comma. So I would probably write a comma there, but I'd say it's not compulsory.

There is also a kind of sentence where the subordinate clause has focus in the sentence, where it contains the most salient point. But that is not the case in your example.

He did not hate Alyona Ivanovna. He killed her because he needed the money.

In this case, a comma would be wrong and unacceptable. Because the focus lies on the subordinate clause, the main clause cannot stand on its own pragmatically (narratively), i.e. this would distort the story line, even though it's possible grammatically (syntactically):

He did not hate Alyona Ivanovna. He killed her, because he needed the money.

This doesn't really make sense as a story or sequence of statements.


I don't think so. The sentence is in form 'A because B', which is one straightforward idea with no subordinate clause.

The only case for a comma might be that A is such a surprising statement that you would want to signal a dramatic pause before 'because' by using a comma. But that does not apply in this case.

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