Whooaaaaa! DavidG from Veritas is ON FIRE today!!!!

What a great discussion.

David, I said that I had made all the comments about this matter that I would make, and that remains the case, so I am leaving all the subsequent posts on it unanswered. I do have to say, though, that I like your two wry references to my remark about infallibility. It's good to to correspond, and disagree, with someone who has a sense of humour: it's rather a rare quality. Regards, Fabio.

iongmat wrote:

GMATGuruNY wrote: SC61:
E: Demographers would have to know a great deal more than now.
Implied comparison:
Demographers would have to know a great deal more than [demographers know] now.
Here, the second clause is NOT in the same tense as the first.
Thus, the verb in brackets -- know -- may NOT be omitted in the second clause.
Eliminate E.

GMATGuruNY, can you please explain this a bit more. Not very clear.

Please revisit my post above, in which I've expanded upon the reasoning.

Thanks for explaining this Mitch.

Among other things, the OG explanation says: the comparison made by the sentence must be between current and conditional knowledge, not between knowledge and time of knowing (now).

Hence I thought that on one side of "than", there is a "time of knowing (now)" while on the other side of "than", there is no "chronological parameter" present. Hence, this is incorrect.

Also, GMAT seems to be slightly flexible in the sense that the verb is not exactly the same in many cases (for example, it seems that simple past can be implied in the second half, when the first clause is simple present). Hence, this is slightly confusing.

iongmat wrote:Thanks for explaining this Mitch.

Among other things, the OG explanation says: the comparison made by the sentence must be between current and conditional knowledge, not between knowledge and time of knowing (now).

Hence I thought that on one side of "than", there is a "time of knowing (now)" while on the other side of "than", there is no "chronological parameter" present. Hence, this is incorrect.

Also, GMAT seems to be slightly flexible in the sense that the verb is not exactly the same in many cases (for example, it seems that simple past can be implied in the second half, when the first clause is simple present). Hence, this is slightly confusing.

The phrase in red seems an overstatement.

One case is SC93 in the OG12:
Heating-oil prices are expected to be higher this year than last because refiners are paying about $5 a barrel more for crude oil than they were last year.
Here, because serves as an adverb modifying are expected to be higher, explaining WHY prices are expected to be higher this year:
Heating-oil prices are expected to be higher this year because refiners are paying about $5 a barrel more for crude oil than they were last year.

If we include the implied words after the first than, we get:
Heating-oil prices are expected to be higher this year than [they were high] last [year] because refiners are paying about $5 a barrel more for crude oil than they were last year.
Here, a reader might construe that because serves to modify were high -- the nearest preceding verb structure -- explaining WHY prices WERE HIGH LAST YEAR.
The result would be a nonsensical meaning:
Heating-oil prices were high last year because refiners are paying about $5 a barrel more for crude oil than they were last year.

In the OA, there is a clear justification for the omission of the verb in brackets, even though the implied tense of this verb differs from that of the preceding verb:
The omission of the bracketed verb makes the sentence CLEARER.

In your post above, the proposed revision of E:
Demographers would have to know a great deal more tomorrow than today.
Here, the two clauses are not only in different tenses but also in different MOODS.
As a result, the omission of the implied verb after than is problematic.
The intended comparison is as follows:
Demographers would have to know a great deal more tomorrow than [they know] today.
Whereas the first verb (would have to know) is in the SUBJUNCTIVE MOOD and serves to express a HYPOTHETICAL action, the second verb (know) is in the INDICATIVE MOOD and serves to express a FACTUAL action.
The differences between the two verbs are far too great to allow for the omission of the second verb.
Thus, this proposed revision of E is not viable.

Hi GMATGuruNY, thanks for your detailed reply.

GMATGuruNY wrote:The phrase in red seems an overstatement.

I believe the following also has a similar issue:

The gyrfalcon, an Arctic bird of prey, has survived a close brush with extinction; its numbers are now five times greater than when the use of DDT was sharply restricted in the early 1970's.

The implied meaning is:

The gyrfalcon, an Arctic bird of prey, has survived a close brush with extinction; its numbers are now five times greater than (its numbers were) when the use of DDT was sharply restricted in the early 1970's.

So, it looks like the tense is again changing from present to past.

GMATGuruNY wrote:One case is SC93 in the OG12:
Heating-oil prices are expected to be higher this year than last because refiners are paying about $5 a barrel more for crude oil than they were last year.
Here, because serves as an adverb modifying are expected to be higher, explaining WHY prices are expected to be higher this year:
Heating-oil prices are expected to be higher this year because refiners are paying about $5 a barrel more for crude oil than they were last year.

If we include the implied words after the first than, we get:
Heating-oil prices are expected to be higher this year than [they were high] last [year] because refiners are paying about $5 a barrel more for crude oil than they were last year.
Here, a reader might construe that because serves to modify were high -- the nearest preceding verb structure -- explaining WHY prices WERE HIGH LAST YEAR.
The result would be a nonsensical meaning:
Heating-oil prices were high last year because refiners are paying about $5 a barrel more for crude oil than they were last year.

In the OA, there is a clear justification for the omission of the verb in brackets, even though the implied tense of this verb differs from that of the preceding verb:
The omission of the bracketed verb makes the sentence CLEARER.

If GMAT really thought that this ambiguity was an issue and if GMAT was really serious about the tense change issue, then the sentence could have been articulated as:

Because refiners are paying about S5 a barrel more for crude oil than they were last year, heating-oil prices are expected to be higher this year than they were last year.

Obviously GMAT writers call the shots, but what I am wondering is that perhaps this tense change is not that big an issue, after all!

GMATGuruNY wrote: Whereas the first verb (would have to know) is in the SUBJUNCTIVE MOOD and serves to express a HYPOTHETICAL action, the second verb (know) is in the INDICATIVE MOOD and serves to express a FACTUAL action.
The differences between the two verbs are far too great to allow for the omission of the second verb.

This is exactly what I am trying to understand: What change in tense/mood is "too great" to allow omission.

iongmat wrote:
This is exactly what I am trying to understand: What change in tense/mood is "too great" to allow omission.

Forms of to be include the following:
infinitive = to be.
simple past singular = was.
simple past plural = were.

Notice what the two OAs below have in common:

Its numbers are now five times greater than [its numbers were] when the use of DDT was sharply restricted.
Heating-oil prices are expected to be higher this year than [heating-oil prices were] last [year].

In each case, the words in brackets are omitted, but their presence is implied.

As indicated by the verbs in red:
Both the antecedent verb in the first clause and the omitted verb in brackets are forms of to be.
The omitted verb in brackets is in the simple past tense.

As indicated by the modifiers in blue:
In each sentence, both clauses conclude with an adverb that refers to time.

The OAs above could imply that an omitted verb in the second clause may be in a different tense from the antecedent verb in the first clause if:
Both verbs are forms of to be.
The omitted verb is in the simple past tense.
Both clauses conclude with an adverb that refers to time.