I'm really confused about adding a comma before an introductory phrase. Here's my original sentence:

"Yesterday I found Susan's missing cat."

I wanted to add the introductory phrase, "While I was getting the mail," after "yesterday," but I didn't know if the sentence should be written like this,

"Yesterday while I was getting the mail, I found Susan's missing cat."


"Yesterday, while I was getting the mail, I found Susan's missing cat."

Is a comma required after "yesterday" when an introductory phrase, such as "While I was getting the mail," or is it preference, just like how it's preference to have a comma after words such as "today," "yesterday," "now"?

  • Or you could write Yesterday—while I was getting the mail—I found Susan's missing cat. with no commas at all. Nov 8 '16 at 21:11
  • Or you could write I found Susan's missing cat yesterday while I was getting the mail with no punctuation at all :-)
    – Frank H.
    Nov 9 '16 at 0:56

All punctuation is a matter of style (and thus preference). There are some rules agreed-upon by style manuals, and two are in play here:

  1. Place a comma after an introductory adverbial clause of suitable length.
  2. Precede non-restrictive elements with a comma; omit the comma for restrictive elements.

Thus, if you mean that you found the cat yesterday, and oh, by the way you happened to be getting the mail, then write

Yesterday, while I was getting the mail, I found Susan's missing cat.

Your getting the mail is an aside, merely additional and less important information, and thus it's nonrestrictive, and the comma goes before while.

If, on the other hand, you mean that you found the cat yesterday while you were getting the mail as opposed to yesterday say, while you were weeding the garden, then write

Yesterday while I was getting the mail, I found Susan's missing cat.

Now, you found the cat at a particular time yesterday, making the the mail retrieval definitional (i.e., restrictive) and no comma goes before while.

Notice in both cases, a comma follows mail to set off the introductory clause from the rest of the sentence.

  • Would you say the same to setting off "hopefully" with commas in a sentence like this: "I want to go to college and hopefully get good grades"?
    – Tim
    Nov 8 '16 at 21:13
  • 1
    @Tim Hopefully is just verbal static. It certainly doesn't mean that you want to obtain your grades in a hopeful manner. It's sort of a substitute for "... and I hope to get good grades." So I'm reluctant to treat it as an adverb like effortlessly (which wouldn't take a comma) or as an aside like as I'm expecting (which would). In my view, punctuation should aid your readers in parsing your sentences (and in particular help them avoid erroneous parsing). A comma or its absence after hopefully neither helps nor hurts, so it's up to you as a matter of style.
    – deadrat
    Nov 8 '16 at 21:54

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