I’ve written before about a comma(,) which muddles meaning, and a comma with restrictive which. The first was in a newspaper editorial, the second in a de Maupassant translation; both were inserted seemingly because of an unfortunate belief in the bogus rule about that and which.
Here, inevitably, is another example, this one in bell hooks’ book All About Love:
Ultimately, though, the authors remained wedded to belief systems, which suggest that there are basic inherent differences between women and men.
The appearance after belief systems of a comma followed by which induces a pause and primes the reader to expect a relative clause about the consequences of remaining wedded to belief systems in general. But that’s not what happens.
First, uninflected suggest implies that the antecedent (what which refers to) is plural, i.e., belief systems, not the (singular) fact that certain authors remain wedded to them. Then the rest of the line shows that the writer is talking about specific belief systems.
So the relative clause is restrictive – the type of belief systems referred to is semantically restricted. Adding a comma makes it non-restrictive, which makes no sense here. I had to reread the sentence to parse it properly, this time ignoring the misleading comma.
Maybe the writer used which rather than that to avoid repeating that (“belief systems that suggest that”), though of course the second that is optional. Or maybe she just preferred which there. Either relative pronoun would have been fine. Adding a comma was not.
Again I’m inclined to think the comma was added by an editor who remains wedded to a belief system* which misinforms them about the grammaticality of which in restrictive clauses in all varieties of English.
Further reading: a discussion among editors on the that/which pseudo-rule. Or see the links above for more detailed discussion.
*
* Note the complete lack of a comma here. Savour it.
Sentence first 
Agh! One of my pet peeves: editors who indiscriminately apply “rules” without consideration of content and context. I consider these folks technicians, not editors.
Some other languages seem not to differentiate between restrictive and non-restrictive clauses in the way that English does. I have, however, heard that Persian has a special pronoun to introduce restrictive relative clauses.
Huddleston and Pullum’s terms ‘integrated’ and ‘supplementary’ for ‘restrictive and ‘non-restrictive’ don’t seem to have caught on, which is a pity because they are more explicit.
Pamela: Yes, the automatic application of rules does readers and writers (and other editors) a disservice. I don’t know for sure that an editor is to blame for this comma, of course. (It’s more likely so in the Guardian example.)
Barrie: I haven’t studied how other languages handle this. And I agree, integrated and supplementary relative are nominally better terms, but they remain very niche, so I tend to use the terms more people will be familiar with.
Stan:
I couldn’t agree more, but I’m more annoyed by the question of comma-tizing or non-commatizing.
Stan, I’ve made you a response! http://editwright.blogspot.com/2013/06/wicked-which-of-stab-in-dark-or-dont.html
Agreed. Why is ‘which’ specially stigmatised? Why don’t editors find the same problems with other wh- words?
Marc: The comma can do the work. This frees up which to be used as writers see fit (and have seen fit for centuries).
paadoty: Thank you! These that/which muddles are a good example of unnecessary rules causing what some linguists call “nervous cluelessness” in uncertain writers, something your post touches on.
Edward: I don’t know; it probably varies from one editor to the next. In many cases I guess it’s simply because they’ve been told, or are following a style guide, and they acquiesce rather than analyse or dispute it.
“Why don’t editors find the same problems with other wh- words?”
I think that, in addition to what Stan said, it’s simply because they don’t see the forest for the trees. I think it takes a little training in linguistics to be able to see the more complex rules governing their use.
My sister and husband has concerns over my structure and grammar. SO I was very happy to have found your blog. I need help in this department. I will be following and wonder if you have any suggestions to offer or perhaps a guide I could purchase to aide in my poor grammar skills. Thanks so much.
Simple Northern Life: Thanks for subscribing. The online Internet Grammar of English covers the basics quite well, while David Crystal has written several accessible grammar books aimed at different levels of expertise.
Thanks so much for answering my questions. Have a great night.
Dear Grammarian: I never would have found your site had it not been for my BloodyBloggingBeginnings! I am a Strunk & White believer–for the most part. About conTroversy: why do Brits do it right? I look forward to your postings and analyses. Oh, The Deluxe Transitive Vampire: The Ultimate Handbook of Grammar for the Innocent, the Eager, and the Doomed is used and loved here in the U.S. (or is that US?). [Note the serial comma: a, b, AND c.]
Thanks for stopping by and joining in the discussion, James. The pronunciation of controversy in Britain is just a different convention, as I’m sure you know; it’s not about its being more or less right than the American pronunciation. For the record, I’m neither American nor British.
I did indeed note your punctuation! You might be interested in what I wrote about the serial comma.