comma with 'which' [relative pronoun]: deal with subjects which

I agree with you, mrve: there should be a comma:).

Hi mrve,

I, too, was taught to put a comma before clauses like that.

Yes, mrve. It is part of understanding the difference between when to use "..., which...", and when to use " ...that... "

MilkyBarKid said:

Yes, mrve. It is part of understanding the difference between when to use "..., which...", and when to use " ...that... "

Click to expand...

Many of his novels are concerned with controversial subjects, which makes them extremely popular.

I, too, would use the comma for the reason mrve gave.

Note, however, that it's not the usual distinction between restrictive (no comma) and non-restrictive (with comma(s)) clauses because even without the comma one cannot simply replace which with that: one needs an AND or something.

Many of his novels are concerned with controversial subjects AND that makes them extremely popular.

I think the peculiarity here is that the verb in the relative clause must change depending on whether its antecedent is singular or plural.

If the fact that his novels are concerned with controversial subjects is the antecedent for the relative clause, the verb should be singular. The relative clause really has to be non-defining/descriptive, so there should also be a comma after subjects.
If the controversial subjects are the antecedent for the relative clause the verb should be plural. The relative clause seems to essential, and should not be separated by a comma. I would prefer to replace which with that.
It's a rather odd sentence, I think.

Many of his novels are concerned with controversial subjects, which makes them extremely popular.

The clause, 'which makes them...' does not help to define 'what novels are we talking about'. Rather, it is additional information - the sentence would stand without it:

Many of his novels are concerned with controversial subjects.

Hence, the use of '..., which...' is grammatically correct here.

Many of his novels are concerned with controversial subjects AND that makes them extremely popular.

'that' is a pronoun in this sentence:'..that( = the controversial subjects) makes them popular. Hence, we have two simple sentences with the conjunction 'and'.

'that' in the earlier sentence is a conjunction.