Commas after introductory words containing a verb form

from Ruge Rules

The Rule: Place a comma after any purely introductory group of words containing a verb form.

As in: Instead of forgetting about the incident, he sought out the culprits.

Or: After working the problem, he sat down.

Or (with an understood, or elliptical, "I am"): Once in bed, I go right to sleep.

BUT: be careful about words at the start of a sentence with a verb among them that are actually the subject of the sentence.

As in: To expect every student to do his or her reasonable best is not to expect too much. (No comma.)


This is in the Harbrace College Handbook, under 12b (1).


Rule 12b(2) pertains to Introductory phrases before independent clauses.
It says, "Omit the comma after introductory prepositional phrases when no misreading would result:

As in: In a crisis we chose Lincoln and FDR. In between we choose what's-his-name.

Compare: Because of this, beauty differs radically from truth and goodness in one very important aspect.