Hi RS1,

This is a really good question! "So" is actually a coordinating conjunction, often used with adjectives to show extremes, and with adverbs to show extreme actions. For example:

Breakfast was so good! <--- "so" is used with the adjective "good," which describes the breakfast.
Brent spoke so quickly that I could not understand him. <--- "so" is used with the adverb "quickly," which describes how fast Brent spoke.

Naturally, there are many other ways we use "so" in sentences. But in the context of your question, let's look at "such," which can be also be combined with an adjective and a noun to show extremes (often in exclamations). For example:

Brent has such a cute baby! <--- "such" is used with the adjective "cute," which describes the noun "baby."
"You have such beautiful features. <--- "such" is used with the adjective "beautiful," which describes the noun "features."

We often use "so" and "such" to show a fact (usually with a result or consequence, either directly using "that," or implying its use).

If both "so" and "such" can be used in conjunction with adjectives, which do you use? The way I use to tell which word to use is to look at whether or not a noun is present. Without the noun present, you need to use "so." The following is correct: "You are so beautiful." The following is INCORRECT: "You are such beautiful."

The coffee was so good that I ordered another cup.
It was such good coffee that I drank two cups. <--- noun present, next to its modifying adjective, "good"

David is so stupid that I won't talk to him anymore.
David is such a stupid man that I won't talk to him anymore. <--- noun present, next to its modifying adjective, "stupid"

In your example, the noun "features" is present in the sentence. Use "such" to pair with the adjective "beautiful."

You have such beautiful features.

I hope this helps!

Hi David,

Thank you for the thorough and clear response. Very useful indeed!

Quick question: If I were to have answer choices in which no choice has the "such+adj+noun" construction, and has only a "so+adj+noun" construction - would the latter be incorrect?

I guess what I am asking is whether "you have so beautiful features" is grammatically incorrect? I completely agree that "you have such beautiful features" is stylistically better.

Thanks!

RS

You're making me dig deep, RS1.

We usually use "so" with an adjective and "such" or "such a" with an adjective and noun.

I say "usually" just in case somebody really clever thinks up an example that counters the rule - there are always cases like that! However, on the GMAT I doubt you will ever come across a case where you don't have an obviously correct answer to choose from, one that has either "so" with an adjective, or "such" with an adjective and noun. They want to test your knowledge of the rules, not to plumb the depths of irregular "crazy-English."

I like that you are persistent about the rules. That will help you achieve success on the exam!