Q. I’ve gone through your section on commas numerous times, yet I can’t seem to find whether a comma would be used in the following instance: “You can be very helpful to your mother or father, or to a person you think of as a parent.”
A. Strictly speaking, the comma in your example is unnecessary. But such a comma may be added if the information that follows the conjunction needs emphasis or is intended as an afterthought—or, as in your example, to help readers navigate a hierarchy of alternatives by providing a sort of shorthand for “on the one hand . . . on the other.”
Even in the simplest of sentences, however, a bit of extra punctuation relative to an “or” or an “and” may be appropriate sometimes. Note how punctuation (or its absence) changes the emphasis in the following examples:
I’ll take an apple or a pear.
I’ll take an apple, or a pear.
I’ll take an apple—or a pear.
I’ll take an apple (or a pear).
I’ll take an apple. Or a pear.
All of these are correct. The conjunction “or” separates the alternatives; adding a comma, a dash, parentheses, or a period emphasizes that break in subtly different ways. But don’t go overboard. In general, it’s best to take a light hand with any punctuation that might be considered optional. When in doubt, leave it out.