A WORD, PLEASE:No clear rule on this, either

I was taught that any little adverb like “too,” “either” or “anyway” that appears at the end of a sentence should be preceded by a comma. I was also taught that saccharin is a smart choice. Take a sentence like, “I was told that steak is good for you, too.”

How do you like that comma before the “too”? I like it just fine. And so does the New York Times in most of the instances I found during a recent search. But I also found some sentences like this:

“The music business is not the only thing that has changed in the eight years since Record Mart last sold a compact disc. The subway has changed too. “

Notice that there’s no comma before that “too”? Sure, it could be an oversight. But because I’m seeing more and more cases like this without the comma, I doubt it. Plus, the very next day, the New York Times reported in an article about India that “books and plays have been banned too.”

The comma-less “too” is outnumbered in the New York Times by their with-comma counterparts by perhaps a 10-to-1 margin. But that’s still 10%.

We see the same thing going on with “either.” Both the New York Times and the Los Angeles Times occasionally eschew the comma before “either.”

“I can’t imagine Janet Nguyen thinking that would be worth it for her either,” a Los Angeles Times reporter wrote.

And another from the New York Times: “Gestures didn’t do much good either.”

I wanted to get to the bottom of this. But a funny thing happened on my way to learning why these commas are going: I realized it’s totally unclear where this comma “rule” comes from in the first place.

My style guides contain lots of very specific instruction on the use of commas in very specific instances. But none address commas before “too,” “either,” “anyway,” etc. at the ends of sentences.

Here, however, are some rules from which we might take some guidance.

“Nonessential phrases” are usually set off by commas, many of my books tell me. So, “My laboratory mice, the little darlings, gobble up that saccharin.” The phrase “the little darlings” is not essential in understanding the rest of the sentence (for those keeping score at home, yes, it counts as an “appositive”).

So does “too” constitute a nonessential phrase in our examples and, if so, is that we usually put a comma before it?

Perhaps. But the reason may instead be that “too” here is functioning as an adverbial — a sentence adverb. And it’s clear that, at least at the beginnings of sentences, sentence adverbs usually get commas.

“Frankly, I’m shocked to learn that Fen-Phen isn’t a weight-loss panacea.”

As many style guides tell us, introductory phrases and clauses often take commas. But the “too,” “either,” etc. situations we’re talking about are not introductory because they come at the ends of sentences.

So what’s the rule you should follow? It appears there is no clear one. There is only convention, the examples of leaders like major newspapers and your own common sense and good ear.

I say, rely on your own judgment. Of course, you should listen to me only if you believe yet another thing I was once taught: Newspapers are trustworthy sources of information.