You should only compare things that can be logically compared. Faulty or nonsensical comparisons account for a significant number of the errors in GMAT Sentence Correction questions. Most of these errors derive from a very simple concept: you can't compare apples to oranges. You are entirely welcome, however, to compare apples to apples, or a long sweater to a long coat, or even the baking of apple turnovers to the baking of pineapple turnovers. That is, on the GMAT, you want to compare only those things that are grammatically or logically similar. For instance, you can't logically compare a person ("Joe") to a quality ("purple"), or an item ("a banana") to a group ("the NYPD"). You have to compare one individual to another individual, one quality to another quality, or one group to another group.

Often, a comparison will sound as though it's acceptable, but will be missing a few necessary words:

Incorrect: The view from this apartment is not nearly as spectacular as from that mountain lodge.

If you read it quickly, this sentence makes perfect sense: the view from the apartment is being compared to the view from the mountain lodge. But if you look more closely, you'll see that the sentence actually compares the view from the apartment to something about the lodge — but what about it?

The comparison needs to be clarified.

Just like misplaced modifier questions, comparison questions can't be judged by the ear alone: even though you might understand what the writer is trying to say, trying doesn't cut it on the GMAT. You have to make sure the sentence actually says what it means to say. Here's the correct version:

The insertion of two little words - "the one" - makes this sentence grammatically correct, because "the view from" now has a partner in comparison: "the one from." An alternative would be to repeat "the view (from)," instead of "the one (from)," in the latter portion.

Incorrect: The view from this apartment is not nearly as spectacular as from that mountain lodge.

Correct: The view from this apartment is not nearly as spectacular as the one from that mountain lodge.

Correct: The view from this apartment is not nearly as spectacular as the view from that mountain lodge.

Let's look at another example.

Shakespeare's plays are different from any other playwrights of his era because they exhibit an exceptional mastery of verse.

Once again, the sentence sounds ok, but it actually compares Shakespeare's plays to other playwrights. The comparison should be between his plays and the plays of other writers.

How can we fix it? We can make the sentence reasonable by inserting a few choice words that clarify the nature of the comparison:

Like the phrase "the one from" in the last example, the phrase "those of" in this example makes it very clear that Shakespeare's plays are being compared to other playwrights' plays – not other playwrights.

Incorrect: Shakespeare's plays are different from any other playwrights of his era because they exhibit an exceptional mastery of verse.

Correct: Shakespeare's plays are different from those of any other playwrights of his era because they exhibit an exceptional mastery of verse.

	You should look out for key comparison words, such as:
	like less than that of	as more than those of	compared to other

Comparison, as a concept, is closely related to parallelism. The basic idea theme is that you should always make perfectly clear to the reader the entities being compared.

Some common phrases used in comparisons are as much as, more than, less than, just like, as, and that of.

5. VERB TIME SEQUENCES

B. Comparisons as Parallelism