Hey William,

I'm not sure where you found this, because it may or may not have been described incorrectly. The FIRST phrase is non-essential, because the second half of the sentence can stand alone. Generally, commas are a good sign that you're dealing with a NON-ESSENTIAL clause. For example, take the most often cited comparison of essential versus non-essential:

The house that I love is on fire.

Notice there are no commas, and we're using the relative pronoun "that" (which you aren't allowed to use commas with). This is essential, because you want people to know which house is on fire, specifically, the one you love.

The house, which I love, is on fire.

This sentence HAS commas with the relative pronoun "which" (you have to use a comma before "which"). This is non-essential. You want people to know the house is on fire, but the fact that you love it is an aside (i.e. non-essential to the meaning of the sentence).

The same would go for your example. However, I'd warn you away from stressing overly about non-essential versus essential. It's a rare split, and I don't think I've ever seen it be the ONLY issue in an SC question.

Hope that helps!

Tommy Wallach
ManhattanGMAT

Hey William,

Well, if you were trying to create sentences from scratch, it'd be a bit more complicated to determine your own sense of essential versus non-essential, but it's pretty fair to assume that when you see commas, you are almost certainly looking at a non-essential relationship, and if you see no commas, you are almost certainly looking at an essential relationship (for grammatical purposes).

Here's where things get hairy. From a purely grammatical standpoint:

Non-essential: Because of the recent decline in enrollment, the admissions office...

Essential: The admissions office decided to reevaluate its recruitment strategies on account of the recent decline in enrollment.

Could you argue that these sentences say THE EXACT same thing? Yes. But the first would be considered non-essential, the second essential.

Thankfully, I don't know of any GMAT question that really tests this particular fact. In the example you gave, did the answer choices really revolve around your ability to differentiate?

Tommy Wallach
ManhattanGMAT