Inflation has made many Americans reevaluate their assumptions about

ELLIPSIS and SUBSTITUTION


NCRanjan , I cannot promise enlightenment, but perhaps I can shed a little light.
I can see why anyone would think that both A and B were correct.
In spoken English, the error in (A) is common.

The answer is indeed an official GMAC answer.

I agree; Americans could be comparing their present living status with that of their parents until now. (In the correct answer, though, did = lived = simple past tense.)
In the "have lived so far" case we would write almost exactly what you wrote, with one change.
The word lived has to be included. "Americans still expect to live better than their parents have lived."
That sentence is correct. We must write both words, "have lived."

When verb tenses change the word "have" cannot stand alone to represent the changed tense. In this sentence we have "live" and "lived."

Have on its own would refer to "live" and would mean "have live."

This sentence that uses have all by itself is not correct: Americans still expect to live better than their parents have.

Unfortunately, we can't create the correct sentence with our options.
lived is not available for omission, and so it cannot be "implied," either—except by the word did.

Further, it's true that past perfect can connote "from the past until now."
We still conjugate past perfect, though, as have lived and present as live. We do not have a lived that we can "imply" by writing have.

When verbs shift in a sentence, only some form of "to do" (almost always do, does, or did) will allow us to imply the verb in a tense that is different from the one explicitly mentioned. We cannot use to do verbs for to be or for have as auxiliary.**

At the same time that we think about using a to do verb, forget about the auxiliary verb "have." We either write "have lived" or use "did."
-- Have does not work the same way as a "to do" word does.
-- Have cannot stand in for a verb whose tense has changed.

• This question involves ellipsis and substitution.
-- In ellipsis, words that are present in the sentence are not repeated.
-- Stated differently, in elliptical construction we omit some words.
Those words are then implied in the places in which they have been omitted.
Often those omitted words will be shortened with substitution—short words that can substitute for the omitted words.

Pure ellipsis, no verb tense shift: He will be a world-class dancer, and she will, too. [Omitted verb phrase: be a world-class dancer]

Ellipsis and substitution (verb tense shift): Electric cars were made to save gas, and they do. [they = electric cars, do = save gas]

• In order to be omitted, however, the exact words first have to be present someplace in the sentence.

On the GMAT, we must be able to insert the omitted words, exactly as they were,
and maintain correct grammar. We cannot change the words that have been omitted. We cannot change "live" to "lived."
Instead, we use the word "did" for "lived."

In other words, because the first verb is live, we cannot insert lived in order to use have lived.
Lived is not present in the original clause.

We could write:
-- They still expect to live better than their parents have lived. (write out the second verb)
-- They still expect to live better than their parents lived. (write out the second verb)
-- They still expect to live better than their parents did. (did = lived)

• Takeaway: the verb that is present "controls" what we may use in elliptical construction. The only verb that can express changed tenses is do (does, did).

Correct: She has not lived better than her parents have [lived].

Incorrect: She does not expect to live better than her parents have.
Problem: LIVED, verbatim, cannot be "implied by omission."
There is no "lived" to omit. In this situation, we use "did."

Live is present and coupled with the first subject, "they."
The second subject, "their parents," is coupled with an "elided" verb (part of the verb is supposed to be implied).

We can attach "live" to the auxiliary verb have that is coupled with "their parents"
to see that the verb tense "have" will not work.
We have only present tense to work with unless we use do, does, or did. With those three, we can change the tense, no problem.

She does not expect to live better than her parents have live.
Present tense "live" does not work with the auxiliary have.
Have does not function in the same way as do. Have cannot stand in for other verbs.

The words do, does, and did often stand in or substitute for verb phrases.
Marisol works harder to finish her college projects than her older sister did.
(Marisol's older sister did not work as hard in college as Marisol works now.)
Andreas liked horror movies as a teenager more than 15-year-old Ricardo does.
(When Andreas was a teenager, he liked horror movies. Ricardo is a teenager who does not like horror movies as much as Andreas liked horror movies at the same age.)

Have and will cannot stand in for verb phrases and shifted verb tenses in the same way that the words do, does, and did can stand in.

Thus in A and B we have

A) . . . they still expect to live better than their parents have [live]

B) . . . they still expect to live better than their parents did [= lived].

Takeaways:
• if elliptical construction is an issue, be sure that the omitted words appear someplace else in the sentence.
If a word was not in the sentence to begin with, we can't "imply" it by omission because there is nothing to omit, but we can use do, does, or did
• if a verb tense shift exists and ellipsis is involved, find the option that both makes the shift clear and does so grammatically. That sentence almost certainly will use do, does, or did.
• do, does, and did are auxiliary verbs that can stand in for entire verb phrases even if the verb tense must shift. Those words often help keep the comparison parallel.

I hope that helps.


*Finally, there are two big exceptions to the "do can stand in for almost any verb" guideline.

A TO DO verb cannot substitute for
-- TO BE verbs, or
-- HAVE, if HAVE is an auxiliary verb.
If have means own, possess, or experience, then have is a "main" verb and can be replaced with do, does, or did.

• TO DO verbs cannot substitute for TO BE verbs
Wrong: She was hungry and he did, too.
Correct: She was hungry and he was [hungry], too.

• TO DO verbs cannot substitute for HAVE when HAVE is a helping/auxiliary verb
Wrong: He had finished his wine and I did, too.
Correct: He had finished his wine and I had, too.

• TO DO verbs can substitute for HAVE when HAVE is a main verb that means own, possess, or experience.
Correct: Artem has ten pennies and Misha has ten pennies.
Correct: Artem has ten pennies and Misha does, too.
Correct: Artem has ten pennies just as Misha does.
does = has [ten pennies]

Correct (did can substitute for main verb had (meaning "to possess")):
Artem had ten pennies and Misha had ten pennies.
Artem had ten pennies and Misha did, too.
Artem had ten pennies just as Misha did.
did = had [ten pennies]