Hi imskpwr - I'm not seeing a non-restrictive clause in your example sentence. The "that" in this sentence is explaining what the linguists theorize, not expanding on the type of linguists that they are.

Wikipedia has examples of how a simple sentence would be re-written with a restrictive vs non-restrictive clause and the comma: https://en.wikipedia.org/wiki/Non-restrictive_clause

essaysnark wrote:Hi imskpwr - I'm not seeing a non-restrictive clause in your example sentence. The "that" in this sentence is explaining what the linguists theorize, not expanding on the type of linguists that they are.

Wikipedia has examples of how a simple sentence would be re-written with a restrictive vs non-restrictive clause and the comma: https://en.wikipedia.org/wiki/Non-restrictive_clause

Certain linguists theorize that although there exist large variations in the thousands of languages, dialects, pidgins, and creoles spoken today by the world's six and a half billion people, the tongues all descended from a common root language.

So, can you tell me what is the role of "coma" that i have underlined?

So, disclaimer here: We're no GMAT experts. But this is what we think you've got going with that sentence:

The main thought is, "Certain linguists theorize that the tongues all descended from a common root language."

The "although" phrase is a subordinate clause; "although" is a subordinate conjunction.

Here's an explanation for this: https://www.beatthegmat.com/comma-rule-f ... 75511.html

You could rephrase this sentence like this: "Although there exist large variations in the thousands of languages, dialects, pidgins, and creoles spoken today by the world's six and a half billion people, certain linguists theorize that the tongues all descended from a common root language."

Does that help?