Commas

A. Any phrase like “trust me” at the beginning of a sentence that is roughly equivalent to a “yes” or a “no” can normally be followed by a comma (as covered in CMOS 6.34):

No, you don’t want to do that.

is like

Trust me, you don’t want to do that.

whereas

Yes, I’ve edited the whole document.

is like

Believe me, I’ve edited the whole document.

and

I swear, I’ve edited the whole document.

You could use a stronger mark of punctuation for extra emphasis:

I swear! It’s not a comma splice!

or

I swear—it’s not a comma splice.

among other possibilities

But a simple comma will be the best choice in most contexts (and won’t get you in trouble for using a comma splice—at least not with us).

A. If you happen to know that the object of your gratitude is a stickler for vocative commas, then write “Thank you, John.” Otherwise (and unless the context is formal), feel free to leave the comma out, a choice that suggests a certain degree of spontaneity and a friendly disregard for the rules. But if you’re an editor of any kind, use the comma regardless of what anyone might think; you have your reputation to maintain. For more on these commas, see CMOS 6.53.

A. Anything intended as an afterthought should be preceded by a comma, or by some other mark of punctuation—a dash, for example (or parentheses). A period could also work. In your example, the comma before “if” is the only thing that tells readers that “if necessary” is an afterthought. So keep it, assuming that’s what you intended.

A. Most style guides published in North America (where the “Month Day, Year” format is preferred) will tell you to use that second comma (the one after the year). This includes not only CMOS (see paragraph 6.38) but also the guides from the Modern Language Association (MLA), the Associated Press (AP), the American Psychological Association (APA), the American Medical Association (AMA), and the US Government Publishing Office (GPO). The guides from Microsoft and Apple also support this rule.*

The idea is that the year is parenthetical—November 3 (2021)—and in your example this usage is relatively straightforward. But when the date is used as a modifier before a noun, the result can seem awkward, and some guides—​including CMOS (in paragraph 5.83)—recommend rephrasing if possible:

The January 10, 2023, decision was unexpected.

or, less awkwardly,

The decision of January 10, 2023, was unexpected.

As for legal contexts, The Bluebook (the legal citation guide published by the Harvard Law Review Association) doesn’t seem to specify how to punctuate dates outside of citations (where a comma might follow a year but for other reasons). But we’d be surprised if The Bluebook’s editors didn’t support the additional comma in a sentence like yours. (A look at the Harvard Law Review’s website suggests a preference for the second comma.)

Verdict: Your law clerks aren’t wrong in this case.

* MLA Handbook (9th ed., 2021), 2.13; AP Stylebook (56th ed, 2022), under “comma”; Publication Manual of the American Psychological Association (7th ed., 2020), 6.3; AMA Manual of Style (11th ed., 2020), 8.2.1.9; GPO Style Manual (2016 ed.), 8.53; Microsoft Style Guide, “Commas” (June 24, 2022); Apple Style Guide (October 2022 ed.), under “dates.”

A. Commas are correct unless an author’s name is being used restrictively, as it is in both instances in the second of the following two examples:

Great Expectations, by Charles Dickens, has gone through many printings.

but

Now that I’ve finally managed to read Great Expectations by Charles Dickens, I’m ready to tackle Great Expectations by Kathy Acker.

In the first example, the phrase “by Charles Dickens” is nonrestrictive; omitting it wouldn’t change the meaning of the sentence (though not all readers will know who wrote Great Expectations). In the second example, omitting the authors’ names would obscure the intended meaning.

For more on the use of commas relative to restrictive and nonrestrictive phrases and clauses, see CMOS 6.27–29.

A. The conjunction “so” can normally begin a sentence without the help of a comma—as can an introductory “and” or “but.” But that doesn’t rule out a comma in every case. Compare these two sentences:

“So where do you want to go next?”
“So, where do you want to go next?”

The comma after “so” in the second example puts the emphasis on that word, making it read as a sort of interjection. In fiction and related genres—particularly in dialogue—this distinction can be important. (See “ ‘Erg, no kidding?’ Interjections in Creative Writing” at CMOS Shop Talk.) In more ordinary prose, however (including your example), such a comma can usually be omitted.

Note that a comma is always omitted when the initial “so” is used as an ordinary conjunction in the sense of “with the result that” or “in order that” rather than as a purely introductory word:

So I wouldn’t miss my stop, I closed my book.

A. Yes, an introductory “also” would normally be followed by a comma. The relevant rule is the one that applies to an introductory adverb like the word yes in the previous sentence (see CMOS 6.34). Note, however, that after an introductory adverbial phrase rather than a single word, the comma can often be omitted, particularly if the phrase is short (see CMOS 6.31). So,

As of late 1999 our Y2K fears still seemed warranted.

but

Also, many of us were new to computers back then.

A. We admire the economy of such a habit, but we can’t endorse it. Not that there isn’t a precedent for such usage. As recently as the nineteenth century, spaces before commas were common, at least in French. Guide pratique du compositeur d’imprimerie, a manual on typesetting by the printer Théotiste Lefèvre that was first published in 1855, reveals as much in a footnote that appears in a section on English composition:

That first line of text (in a detail from page 182) says that in English practice there’s no space between a comma (“virgule” in French) and the word that it’s next to (i.e., the word that it follows). Footnote number 3 steps in to allow M. Lefèvre to observe that not only is this unfortunate (“vicieux” is as bad as it sounds), but worse, it’s happening more and more in French works.

In Lefèvre’s book, space appears before commas, with two exceptions: (a) where the line of type is too crowded to allow for any and (b) next to r’s, v’s, and y’s. The latter were exempt, “parce que ces trois lettres portent un blanc suffisamment fort par en bas” (i.e., those three letters already leave enough space along the baseline; see Lefèvre, p. 30).

Go back even earlier in time, and the practice was to remove the space after the comma also—à la your academic friend—but only to accommodate very tight lines of justified text. In English, such commas with no space before or after can be seen in the earliest printings of the King James Bible (1611). This same usage could be seen at about the same time in Spanish in the novel Don Quixote (1605 for the first volume).

Back to the present: nobody puts spaces before commas in published prose anymore, and there are only two common scenarios in which the space after the comma is customarily omitted: next to a closing quotation mark, “like this,” and between digits in numbers like 1,132.

A. Though the serial comma has officially been Chicago style since 1906 (when the first edition of the Manual was published), we prefer to omit it before an ampersand (see CMOS 6.21). The serial comma—the one before the conjunction in a series of three or more (it’s also known as the Oxford comma)—suggests thoroughness (some consider it to be unnecessary); the ampersand, by contrast, is an abbreviation (derived from the Latin word et, or “and”). The two together, then, make for an odd pairing of the thorough and the minimal. Either remove the comma or spell out the word “and.”

A. Not usually. For example, both of the following would be correct:

But I don’t want to meddle.

And to avoid getting my feet wet, I wore boots.

The rule is the same as when the conjunction introduces an independent clause within a sentence (usually following a comma; see CMOS 6.22):

I’d tell you how to punctuate this sentence, but I don’t want to meddle.

I carried an umbrella, and to avoid getting my feet wet, I wore boots.

but

I carried an umbrella and, to avoid getting my feet wet, wore boots.

It wouldn’t be strictly wrong to add a comma after the conjunction in the second and fourth examples (see CMOS 6.26), but Chicago usually prefers to omit it unless the conjunction joins a compound predicate (as in the fifth example; see CMOS 6.32). The same logic could be extended to similar constructions that might otherwise call for two commas. For example,

But Jerome, we haven’t yet discussed commas.

Some editors would add a comma before “Jerome” (see CMOS 6.53), but unless you’re applying or enforcing a comma-heavy style, you can omit it.