Q. Hello, Chicago. Thanks for your time. I’d like you to confirm the optional comma after a one-word adverb of time (tonight, yesterday, today) starting a sentence. One of my fiction authors is upset because Word is showing blue lines under those words. I told her a comma is optional and Word doesn’t get the nuances. Would you please confirm this so I can calm my jittery author? Thanks again.
A. It can be hard to ignore Microsoft Word’s blue underlines, especially when they’re worded in a way that suggests you’d be wrong to keep the text as is: “After an introductory word or phrase, a comma is best.”
But you can tell your author that we agree with you. In the words of CMOS 6.34, “Although an introductory adverbial phrase can usually be followed by a comma, it need not be unless misreading is likely. Shorter adverbial phrases are less likely to merit a comma than longer ones.”
The adverbs yesterday, tonight, and today aren’t phrases, but each of them derives from one (yesterday comes from Old English giestran dæg), and it’s clear that each is grammatically equivalent to a phrase like next week or in 1965. Plus, any one of these words would qualify as short in the context of introductory adverbial phrases.
To be fair to Word, tonight is the only one among the words and phrases mentioned above (from yesterday through in 1965) that Word’s grammar checker flagged in our tests when it wasn’t followed by a comma (as of July 1, 2025). Conversely, Word didn’t stop on any of them when they were followed by a comma. So it’s not that far out of line with CMOS.
Tip: To avoid falling under the influence of Word’s blue underlines, some writers prefer to toggle them off as they draft. A convenient way of doing this is to add a button to the ribbon. In Word for Windows (the desktop version), go to File > Options > Customize Ribbon. Then select All Commands under “Choose commands from” and scroll down until you find Hide Grammar Errors. You can then add that command to a new group under the Home tab (or wherever you want it to appear). Steps for Word for Mac will be similar.
If you use the option under Customize Ribbon to assign a keyboard shortcut to the equivalent command (look for ToolsGrammarHide under the All Commands category in the separate dialog box for keyboard shortcuts), keep the button, which has the important advantage of showing whether it’s on or off (via shading/outline).