comma + ing verb (RULES)

[JackC922]

I know that a comma + ing verb needs to describe the actions/result of the entire prior phrase. However, what happens if a comma + ing word follows a non-essential modifier (which itself follows the main clause). If correct, should the comma + ing word be describing the actions (modifying) the immediate prior phrase, the non-essential phrase? Or does the rule state that comma + ing words need to describe the actions/results of the entire prior MAIN phrase?

Example
• Independent main phrase, modifying non-essential clause, ing word phrase

If correct should the last phrase be modifying the middle clause that it follows, or the first main phrase?

[StaceyKoprince]

Good question! This is actually the source of a common trap on the GMAT.

Officially, the comma –ing modifier modifies the main action, even when there's something in between the comma –ing and the main action.

But when you have a setup like you describe:
Independent main phrase, modifying non-essential clause, ing word phrase

If that middle part, the modifying clause, itself contains a different action, then this structure can introduce ambiguity. Which action is the comma –ing mod actually modifying? I've seen multiple OG explanations that call this out as ambiguous / a reason to eliminate an answer choice.

That's not to say that you can never have a middle modifier separating the main action from the comma –ing modifier. But you'd have to make sure that the meaning was clear. That comma –ing has to unambiguously refer to the main action.

On the GMAT, if they are actually testing this structure (ie, it's part of the underline and there are some answers that avoid this structure), then this structure is usually wrong.