Would this be a good time to mention that “that” is woefully misused when referring to people. You can eliminate a lot of “thats” by using “who” instead.
“The person that performed the work showed up late.”
“The person who performed the work showed up late.”
The second sentence sounds much better to my ears and is my own personal preference, even though “that” isn’t technically incorrect.
I’ve noticed the opposite to be true also. A lot of inanimate objects get referred as “who.”
How do you know that which is to be used instead of that?
Your rule seems to me to be circular.
I follow Colibri’s rule, with one exception: Sometimes you can find yourself in a situation where ‘that’ has already been used in a sentence, and therefore sounds clunky if used again. But in those cases it’s often better to rewrite the sentence.
You did not!
I *think *the point is this:
If you’re a writer who, unlike me, doesn’t sprinkle comma slices all throughout longish, and digressive, not to mention subjunctive, sentences, but instead can carefully, and correctly, use commas in all their myriad uses, places, and styles, then it’s pretty easy to use the rule as **Exapno **and others suggest.
If you build a sentence like:I want to use a pot [that/which] is big enough to hold all the ingredients with room to simmer without boiling over.Then since it naturally and correctly contains no comma the correct choice is “that”.
Conversely, if you build a sentence like:
My favorite pot, [that/which] I inherited from my Mom, is big enough to hold all the ingredients with room to simmer without boiling over.Then since it naturally and correctly includes a comma the correct choice is “which”.
Which, as has been said, depends critically on the writer already being able to operate commas and sub-clauses correctly. But for somebody who can operate commas but thinks/thought of “that” vs. “which” as interchangeable or a complete mystery, the rule is pretty easy to remember and to follow. Wish me luck 
My rule: if “that” sounds right, use it. Otherwise use “which”. Works like a charm.
I’m not sure, but I’m guessing you think I incorrectly used apostrophes in plurals.
Nope. It’s a variation of 6.10 in the Chicago Manual of Style.
You also use the 's with words that you want to hold form with. That and which don’t have regular plurals and using “thats and whiches” would de-emphasize the base word.
It’s an unusual construction, one you don’t see outside of formal word discussions because it’s not necessary elsewhere. What it isn’t is the use of apostrophe’s in plural’s.
I understand the point. My point is that the rule works best for people who already know how to use commas (which I also understand is what you are saying).
In the sentence “The bicycle[,] [which/that] is red[,] is next to the house,” the meaning will determine both whether commas are needed to separate the clause, and which word is needed to introduce it. You need to decide on both simultaneously.
What if they both sound right?
Point taken. Thanks.
If they both sound right I always choose “which”. It sounds more specific to me, and I’m always striving for high (or is that obsessively excessive) specificity. Does that match any commonly accepted set of style rules? Don’t know and heretofore haven’t cared. But I’m trying. 
While true, the current trend is to use italics in this context, with the s not being in italics. I’ve seen that recommended in many of the same places where I would send people to show them that using an apostrophe was acceptable.
Unfortunately, I don’t have access to the CMoS to see if they allow this, and I’m not having much luck finding a quotation. Personally, I think the fact that the CMoS is paywalled is a good reason not to use it unless you are required to do so.
Whether or not there are any trends involved, Exapno is perfectly correct in stating that his choice of style is an accepted practice.
And the Chicago Manual of Style is a style manual used by many reputable publishers. Disregarding its advice because it is not free online is a ridiculous standard.
In any case, I’m curious as to what your actual point is in quarreling with Exapno. Unless the SDMB adopts its own style manual for posters, then he is perfectly justified using a long-respected and widely used style manual to support his usage.
No, in fact it might be considered the reverse of the usual rule. As in my examples above, “the bike that is red” specifies that one is speaking about a particular red bike, while in “the bike, which is red” the fact that it is bike is red is not crucial to the sentence.
Cite, especially that this is an increasing practice? I can’t say that I’ve ever seen this in a standard publication, and both CMoS and AP recommend Exapno’s format.
There’s no reason to use any particular style unless it’s for publication. And if you’re publishing something, you’ll need to use the publisher’s style. So if it’s CMoS, you’ll just have to shell out for it.
I’ve never seen the form cited by BigT and would like to see examples. Of course styles change over time and my old CMoS13 is a couple of editions behind the times. And of course everybody else is right that no particular style guide is meaningful unless you are required to use one.
I cited CMoS because after Mighty_Girl pointed it out I could see how someone not familiar with the style would raise an eyebrow. It’s not common and I can also see how modern practice may differ with the old, precisely because the misuse of apostrophes has made everyone hypersensitive.
I’ve got the most recent edition (16th) and the rule is still the same. For AP I have the 2011 edition.
The painting that was in the foyer was stolen. Here you are identifying which painting was stolen.
The painting, which was a poor copy of the Mona Lisa, was stolen. Here you are telling a bit more about the painting.
-or-
*Colibri’s bicycle example, post #4.
(cite: English Teacher From Hell - for a Mother. I did get revenge, nailing her grammar and diction.)
That must have been Hell. I remember one English teacher in junior high. Her twin sons were my age and my classmates. They were two of the main bullies in school. I’ve always wondered if that had anything to do with the mother.
I never knew that bit about Brits being more easygoing with “which” and “that.” I think it’s interesting because–rightly or wrongly I’ve always thought they were stricter, in educated English speakers, with grammatical distinctions.
Worth thinking about, although perhaps not here.
Use “that”. Read what I wrote, which makes it clear.