Sentence correction problem

[markebest]

If which is used without a comma in sentence correction would this always be wrong since which introduces a non-essential modifier and a non-essential modifier is indicated by a comma? Would the reverse always be true with that?

Thanks

[ayang]

It is in fact the case that 'which', which generally introduces a non-essential modifier (as in this sentence), is correctly introduced by a comma. For example, in the Verbal Official Guide (the purple guide) Sentence Correction #73, the correct answer reads:

Analysts blamed May's sluggish retail sales on unexciting merchandise as well as the weather, which was colder and wetter than usual in some regions, slowing sales of barbecue grills and lawn furniture.

Also, the phrase 'to which' can be used correctly in many different contexts. For example, in Official Guide (the orange guide) Sentence Correction #131:

their language is basically seventeenth-century French to which English, Spanish, and Italian words have been added.

However, one should not apply a blanket rule that 'which' demands a comma to accompany it in all cases when introducing a modifier, though this will generally be the case. This falls into a category of a rule that will generally apply, but it is possible that a gramatically correct sentence on the GMAT will use this construction, and that other answer choices will have more serious problems.

The reverse is not always true (i.e. it is not the case that every non-essential modifier set off by commas is introduced by 'which').

I hope that this is helpful. - Andrew

[liu1993918]

Can I ask about this sentence mentioned above?
Analysts blamed May's sluggish retail sales on unexciting merchandise as well as the weather, which was colder and wetter than usual in some regions, slowing sales of barbecue grills and lawn furniture.

My question is that “slowing" seems have no relationship with the main sentence but modifies weather. However, according to my previous studies, I learned a rule about "the S V O, ING" that slowing must apply to the Subject. Thus, This rule doesn't apply to this sentence, right? So, the rule is wrong?

[RonPurewal]

It applies to the closest action. In this case, that action is "...which was colder and wetter than usual". The relationship to the slowdown in sales is clear.

(The subject of that action is "which", which in turn refers to the weather-- so that makes sense, too.)