Restrictive or Non-restrictive

First the example:

The Sapelo Island Lighthouse is the second-oldest brick lighthouse in the country dating back to 1820.

https://blog.thediscoverer.com/10-best-usa-islands-outside-hawaii/

Here’s a picture of the lighthouse:

Sometimes you use a phrase (no verb) or a clause (has a verb) to describe something. When you separate that description from what it describes with a comma, we call it non-restrictive. It’s an aside. No comma? Then it’s restrictive, part of the definition of what you’re describing.

That’s a little bit tricky to follow, so let’s look at that sentence about the lighthouse.

It’s the second-oldest brick lighthouse in the country. So far, so good. But what about “dating back to 1820”?

• Is it the second oldest one that dates back to 1820?
• Is it the second oldest one, and it happens to date back to 1820?

The first bullet is restrictive, part of the definition. Apparently we have lots of lighthouses that date back to then, and this is the second oldest. Seems unlikely.

The second bullet merely adds some information about the lighthouse; it dates back to 1820. It’s non-restrictive.

What a difference a day comma makes!

Remember: no comma, gotta have it—restrictive. Comma, extra info—non-restrictive.

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I can’t resist. Kind of a double whammy…

Saturday Morning Breakfast Cereal is a good intellectual humor comic. You ought to subscribe to it.

In case you didn’t get it, the oxford comma is the one that goes before the “and” when you have a list of things.

Commas separate things. Dates from years, cities from states, and so on. Another thing they separate is direct address, as shown below:

The more astute among you might suggest that the maybe guy was using an appositive, explaining what was to be eaten. Good point, but that’s a bigger break than a comma can handle, so in that case, he should have used an M-dash:

Would you like the all-you-can-eat—shrimp!

The hyphens and the cook are both correct, by the way.

Some punctuation puns.

I should add that an M-dash is three times longer than a hyphen. And be sure to pronounce the second “s” in asterisk.

I chose this example of the importance of correct comma usage partly because the article I found it in was interesting.

Here’s the rule:

Words and phrases between two commas are an aside, and can be removed from the sentence; the sentence still stands.

Here’s the example. Think about the meaning if you take out that second comma.

Amazon bought online pharmacy PillPack, a startup that ships medication directly to customers, for $1 billion.

https://www.wired.com/story/why-hard-escape-amazons-long-reach

See the difference? As the sentence stands, they bought PillPack for a billion dollars. If you take that comma out, you have PillPack shipping meds for a billion. More than I’d want to pay for some pills!

The article in the link is interesting—Amazon is rather diversified.