Grammar questions answered: Restrictive and non-restrictive

I asked for some grammar questions, expecting/wanting some softballs. Ha! Not a chance. But I will throw myself to the wolves and try to answer.

Stacey asked-
Here's my question(s): What is a restrictive clause? What does it mean, really? What makes it restrictive?

I ask this, because I have a note that says if I'm using the word "which" in a restrictive clause, I should replace it with "that." It would be a helpful note if I knew what it meant! Hahaha! :)
 Okay, to get very basic, a clause is an element which has a subject and verb, and it can be "independent" (can be a sentence on its own, like This will be a long and tedious explanation), or dependent, (which can't be a complete sentence on its own, like which will be hard to understand). 
 Dependent clauses can be used in many ways in a sentence, like to establish some time or place condition--
When I was young, we used to have to walk three miles uphill to school.
or
Wherever we stay that night, we should get a suite with a view of the river.
"Restrictive" clauses are special types of  "relative" clauses. (A relative clause – I know, this gets arcane, but you know, you say and write these every day, even if you don't know the terms—is a clause which "relate" one thing to another. Forget that—just know that relative clauses start with those relative pronouns—who, which, that, what— and then have a verb, like Relative pronouns, which include "which and who," are how relative clauses start.) Relative nouns are usually "adjectival", modifying a noun (often but not always the subject of the sentence). So they are usually used as "appositives" and tell more about the noun that precedes them:  Governors, who serve a four-year term, are the chief executives of their states.
 You can see there that the relative clause—the appositive—just tells us more about governors. (Not all appositives are clauses—they can just be phrases, like The lady in the red hat ordered the soy latte. But let's not deal with that now. :)
What's important in that example is that it tells us more about ALL governors- that is, the meaning of the noun governor isn't narrowed by the appositive. ALL governors serve a four-year term.
 That is a NON-restrictive clause. It tells us more information about the noun it modifies, but it doesn't "restrict" the noun.

Relative clauses can be restrictive or non restrictive.  That is, they either restrict or don't restrict the noun they modify.

Let's come up with a RESTRICTIVE appositive/relative clause (so many terms! But "appositive" is syntactical—about the role this plays in this particular sentence—while "relative clause" is a grammatical term… well, never mind J).  
A restrictive clause will "restrict" or narrow the meaning of the noun it modifies, like:
Governors who take bribes should be impeached.
In this case, the relative "who" clause "restricts" the noun to a specific and narrow meaning. There are many governors, but in this case, I'm speaking only of the ones who take bribes. I'm not saying every governor should be impeached, only that special group who take bribes (I'm hoping that's a small percentage of them!). The restrictive clause stuck in there actually "restricts" the noun, see.
Now the noun phrase isn't just the single word "governors," but the narrower term "governors who take bribes."

Let's diagram both those sentences:
Subject (noun phrase)
Predicate (verb phrase)
Governors, who serve a four-year term, are the chief executives of their states.
Governors who take bribes should be impeached.
See the difference? Who are the chief executives of the states? Governors. You can take the appositive clause out and the main clause still means what you want it to mean—
Governors are the chief executives of their states.
But see what happens when you take the appositive out of the second one:
Governors should be impeached.
Even if we don't like politicians, we probably don't mean that all governors should be impeached!

So…
Relative clause (who/which/what/that + verb)
Appositive (a clause or phrase which explains more about a noun)
Restrictive clause (a relative clause which "restricts" the meaning of a noun) Governors who take bribes should be impeached. This is NOT set off with commas before and after because it is necessary to the meaning and actually becomes part of the noun.
Non-restrictive clause (a relative clause which explains more about a noun but doesn't restrict the meaning)- Governors, who serve a four-year term, are the chief executives of their states. These are set off before and after with commas, to show that they are "unnecessary" to the meaning.
--
What about "which and that"?
They are both "relative pronouns" which start relative clauses.
"Which" is used in non-restrictive clauses JUST BECAUSE. (I mean, I don't know why.) That means you use commas before "which"—not because it's "which," but because it's non-restrictive, which uses "which".
"That" means exactly the same thing, but is used with restrictive clauses and no commas.
(With people, btw, no matter what, we use "who." Also, my cat, WHO is named Bandit, reminds me we also use "who" with pets.)

Restrictive clause –  Pedestrian malls that are successful share three important factors. (that is, we're only talking about successful pedestrian malls).

(People= who) Pedestrians who cross against the light are taking a big risk. (Only those who cross against the light are taking a big risk.)

Non-restrictive clause -- Pedestrian malls, which limit car traffic on downtown streets, are popular with businesses because they increase foot traffic. (All pedestrian malls are popular with businesses.)

Pedestrians, who are often walking for their health, are tempted by the bakeries which line Ontario Street.

What do you think? Does that make sense?  Often if you speak the sentence aloud, you can tell if you mean the more narrow subject ("Governors who take bribes"), as you will speak that without the pause that would indicate commas.

Restrictive vs. nonrestrictive always gives me a headache to explain, and anyway, it's been explained better by others:
Restrictive_and_Nonrestrictive
Another site for this
Check these out. :)

Simple Edit

Sometimes we come across a sentence structured like this:

There/It (subject)
was/were (verb)
someone/something (direct object)
who/which/that (relative pronoun)
did something (relative pronoun clause)

There was an old woman who lived in a shoe.

It was a face that only a mother could love.

This creates a slight wordiness and relegates the impact ideas to a dependent structural position in the sentence. Fix it by killing the flat subject/verb, cutting the relative pronoun, and rearranging the remaining words into a simple sentence.

An old woman lived in a shoe.

Only a mother could love that face.

You see how that works? It's not all-purpose, but it will yield a stronger sentence in the majority of cases.

Theresa

Extremely minor point

This is pretty minor, but my mind flagged it as I read, and I thought it might be an example of the reason it's good to keep sentences as simple as you can, to make that an actual part of revision.

Here's the sentence, from a NYT article on California's water problems (you Californians must feel like a plague of locusts is next)--

...(I)t was Mark Twain who was believed to have said, “Whiskey is for drinking; water is for fighting over” ....

What's wrong? Well, the awkwardness of that "who was believed" is a clue. It's actually introducing a new "character"-- the unidentified person or persons who believed Twain said that. Notice the passive construction-- well, how this forces a perfectly active subject/verb (Twain said) combo into passivity (Twain... was believed, and who believed is never stated, so passive), and then into some weird past perfect tense, and for what? To indicate that the reporter isn't sure Twain really said that? (I do understand-- I'm sure he never said a lot of the pithy quotes attributed to him.) But then also the past tense there -- was believed? So he's no longer believed?-- starts forcing questions on us (who believed that, do they still believe that), and why? Why construct a sentence that opens up so many irrelevant issues? If you want to use the quote, go ahead, but simplify the sentence so it says ONLY what you want it to say:

Twain said this maybe
Here's what he maybe said

What's the problem? Well, first, "it was Mark Twain" diminishes the sentence's true subject (Mark Twain, the one that did the action of saying) into a predicate nominative (what "it" was), thereby diminishing the importance of the most important word. There are reasons to use "it was" there-- for rhythm, for a longer sentence-- but the tradeoff is wordiness-- and an editor (obviously not the NYTimes editor:) will probably try to cut that and put Mark Twain in the pride of place-- the subject position.

Second, it's that darned relative clause:
... who was believed....

Relative clauses are adjectival usually, modifying a noun-- here Twain (they can be adverbial and modify a verb, but that's less common). Relative clauses start with a relative pronoun (usually who or which). Clauses of any kind take on more importance in the sentence just because they're clauses and have a subject and verb (Subject -- who, verb-- was believed). But that means that relative clauses (which are JUST modifiers, that is, not syntactically that important) often distract from the main clause of the sentence, especially when they break up the subject/verb sequence as here.

The first technique to trim and simplify a sentence is to decrease relative clauses to a modifying word or phrase. Doing that will put the emphasis back on the most important elements (subject and verb-- actor and action), and also get rid of that distracting and complicating clause in the middle of the sentence.

So how would I edit this? Well, the "who was believed" is really meant to say, "Twain is reputed to have said this." So go with an adverb that modifies the verb! After all, it's the verb (said) that you want to call into doubt, not Twain-- Twain did exist, so HE is not alleged. It's his saying this that is alleged. Also if I diminish this from a clause (which needs a verb and so tense) to an adverb, I just move around the issue of tense (is he still believed to have said that, or was it only in the past he was believed) by not presenting it as an issue in the "was".

So:

Mark Twain supposedly (allegedly, reputedly) said, "===."

Or I might make the quote tag a dependent clause, and the quote the main clause, depending on whether I want the emphasis on Twain or the quote:

As Mark Twain allegedly said, “Whiskey is for drinking; water is for fighting over” ....

To simplify, determine what's important in the sentence, and make that or those the clauses, and avoid making the less important thoughts into clauses. Simple! :)

Alicia