Two questions of clarification:

1.) Is it period then ellipsis, or ellipsis then period? (I assume the first, but I thought I'd check.)

2.) What is the different in usage between an en dash and an em dash?

Regarding the prohibition of using the apostrophe for plurals:
[hypothetically] I work with a machine with model number S-1a. Must I make the plural as S-1as? What do I do about the fact that there is another model of the machine which just happens to be S-1as, a sub-model which incorporates an "s" modification? Yes, I can always write the singular model number and use some other device to indicate plurality, but S-1a's would be simpler, I think.

Abigail,
1. Yes, the period comes first.
2. An en dash is used for numerical ranges (the years 1985–1988, questions 6–10, 3–5 minutes, etc.) and in place of a hyphen in a compound adjective when one of the adjectives has 2 words, e.g., blue cheese–onion burger (that is, a burger made of blue cheese and onion, as opposed to a cheese and onion burger that happens to be blue). An em dash is used to indicate a break in thought, sort of like a comma or colon. (Although I do occasionally use a pair of em dashes in place of a pair of commas if there are already other commas in the sentence, just for clarity.)

Nicely summarized; I'm sure Lynne Truss would be pleased. (I hope I used that semicolon correctly.)

Dave

It seems to me, being one of those who gets wrapped up in minutiae like commas, that anyone who likes usage and grammar enough to peruse your blog does not need to refer to this list. The real patients who need to take this medicine are somewhere else.

A dozen exclamation points? How generous! I come from the John Kupetz school of thought - you get ONE. Ever.

(In professional writing; I didn't just waste my one in this comment.)

"Is it period then ellipsis, or ellipsis then period? (I assume the first, but I thought I'd check.)"

Period before ellipsis when the omitted material is part of a new sentence; period after ellipsis when the omitted material is part of the same sentence.

"The careful editor understands that many writers punctuate from intuition rather than training // and // that correction is often required."

But commas, in particular, should match the intonation of the spoken words, and this sometimes requires placing a comma where a strict application of the rules would prohibit it.

In the example below your seventh resolution, could you use a colon instead of a dash?

Journalists // , // who have often been recipients of bad advice on language // , // can receive assistance from an unlikely source // : // the copy desk.

Sure.

In re: The audience for this blog. In addition to the adept, there are some novices, some students, some shy people who are apparently hesitant to post anything lest I leap out of the shadows and pounce on them for their errors.

If you are among the adept, carry the word forward.

...there are some...shy people who are apparently hesitant to post anything lest I leap out of the shadows and pounce on them for their errors.

We have established that you, Mr. McIntyre, are a gentleman.

It is the Robins of the world we fear.

Bucky, you have cut me to the quick. I shall go and darken this blog no more.

ooh, ooh, I found a typo!
(see header of resolutions)

Resolved: That I will refrain from using dashes for merely parenthetical material, using parentheses or commas instead, reserving the dash to indicate a break in continuity.

I'm not sure I'll be joining you wholeheartedly here--I think I'll simply perch on the edge of the bench.

I do agree that the paired dash is overused, but sometimes those parenthetical dashes please me. When the parenthetical thought is interjectory enough, at least.

Yes, patricia, you did, and I don't begrudge you your glee. It's fixed.

Now, Bucky, now Robin, be nice. Don't make me come back there.

Resolved: That I will use an apostrophe in the contracted form of "it is" and will never, ever even think of using one in the possessive form of "it."

I'm with Talley Sue Hohlfeld on dashes, perhaps because I've used them that way at times. They do look odd on the page, but so do parentheses. I'm also inclined to think that rules three and four on superfluous commas are more like guidelines than absolutes. If you look at commas as the print equivalent of pauses, they could sensibly be used in violation of these rules, especially in long sentences. Good list, though. A restaurant down the street from my house had a large sign advertising "wing's." It burned down last month. Serve 'em right.

Resolved: That I will use square brackets, not parentheses to set off interpolated matter, no matter what the Associated Press does.
Isn't it "... brackets, not parentheses, to set off ..."?
I work for a math publisher, and I always use "2s and 3s," no apostrophe. Do you also agree with the NYTimes on dates, as in "the 1980's"? Isn't it just a style issue, not a rule?

Robin wrote: Bucky, you have cut me to the quick. I shall go and darken this blog no more.

Robin, my apologies. What I said sounded mean; it wasn't intended to be.

I come here all the time and I'm maybe one of the worst punctuators ever. For a long time, I wouldn't comment on this blog, even when the subject was martinis or bow ties, for fear of making a mistake with a comma or semi-colon. Or a dash. Yeah, a dash. Dashes are the worst of all. Well, then there are ellipses...

Anyway, bad punctuators like me live in mortal fear of good punctuators.

But you should not deny yourself the pleasure of Mr. McIntyre's blog because I made an ill-advised public confession about who (or is it whom?) I fear.

I have exhausted my supply of exclamation points.

I note that you avoided reference to the serial comma, an issue about which I was ready to resolve with swords at dawn on a barren heath. Having been drilled by the founding headmaster of the Ranney School that the proper usage was "red, white, and blue," I worked hard to maintain that standard as I worked as a production editor at Prentice-Hall publishers and later as a public relations hack, for a while with the support of a newspaperman groomed in the 50s and 60s. More recently, in a variation on that hackery, I have been overruled by more recently trained newspaper writers, and I have relented, not because I've changed my mind about the logic of the serial comma, but because the final decision rests with others, and I see no point in making them remove commas that I have inserted into their copy. In my own writing, however, I continue to treasure what seems to have become an archaism.