Ozone reaches high concentrations twelve miles

[tim]

You're welcome..

[violetwind]

Ozone reaches high concentrations twelve miles above Earth, where it has long appeared that it was immune from human influence; we have now realized, though, that emissions of industrial chlorofluorocarbons deplete the ozone layer.

A) has long appeared that it was immune from

B) has long appeared to have been immune from

C) has long appeared as being immune to

D) had long appeared immune to

E) had long appeared that it was immune to

I could figure out that "immune to" is better than "immune from". C lost out because of "being". But I could not choose between D and E.
Could you please explain.

Thanks

Hi Ron, I kinda get what you explained about "had appeared", but still need a little clarification. Is it because there's a "have realized"(means past), then we must use "had appeared" to imply "past of the past"? In other words, if I put the verbs in this sentence in a time order, it should be :appear immune--->realize-->reach , right?

but why the clause following realize(past) is a simple present tense(deplete), which means it happens at present?

[tim]

Your analysis of the past perfect in this case is correct. As for the present tense being used with "deplete", this is because the depletion actually does occur in the present. We realized that at some point in the past, but it is something that does occur in the present..

[NYCFox]

Ozone reaches high concentrations twelve miles above Earth, where it has long appeared that it was immune from human influence; we have now realized, though, that emissions of industrial chlorofluorocarbons deplete the ozone layer.

had long appeared immune to
has long appeared immune to

I ignored had, thinking that there is no past event. I was under an impression that the past event and an earlier past must be parts of the same independent clause AND must be related. Guess I was wrong.

Here, the past event is taken from the second sentence;
"we have realized"-- Event is realized

Past perfect from first:
"it had long appeared"-- Appeared

I believe, the sentence is conveying this

Before we realized that Ozone layer was actually vulnerable to human influence, it had appeared immune.
Sounds awkward.

Before we realized that Ozone layer was actually vulnerable to human influence, we had thought it was immune.
Looks better and more related.

Is my interpretation correct? Any comment?

[RonPurewal]

I believe, the sentence is conveying this

Before we realized that Ozone layer was actually vulnerable to human influence, it had appeared immune.
Sounds awkward.

Before we realized that Ozone layer was actually vulnerable to human influence, we had thought it was immune.
Looks better and more related.

Is my interpretation correct? Any comment?

it appears that you're trying to posit some sort of difference between these two -- but i don't see exactly what that difference is. in terms of meaning, these two sentences are more or less the same; "it had appeared immune..." and "we had thought it immune..." have the same meaning.
for another illustration of why this is so, imagine that i look at a friend and say one of the following two things:
you appear to be sick.
i think you are sick.
these two are not appreciably different. both refer to my perception that my friend is sick.

in any case, the simplest way to knock out the choices starting with "has appeared" is to realize that this is not a state persisting all the way up to the present.
from the context of the sentence, we can figure out that this state persisted only until the discovery that the ozone layer was being depleted (a past point).

note also that if you can eliminate the other incorrect constructions in the first three choices, then you don't have to bother with the verb tenses. this situation is very common, actually: on this exam, verb tenses are VERY RARELY tested alone. you should make them a lower priority than more important topics, such as parallelism, pronouns, etc.

[namnam123]

Is there any difference between immune from and immune to?

the former is unidiomatic (wrong).
the latter is idiomatic (correct).
that's the difference.

remember, idioms don't follow rules; you just have to memorize them, one at a time, if you don't know them.

Ron, I agree with you that "immune to " is idiomatic. But in the dictionary, "immune from " is good. I wish you, Ron, to comment on this.

[RonPurewal]

Ron, I agree with you that "immune to " is idiomatic. But in the dictionary, "immune from " is good. I wish you, Ron, to comment on this.

yes, "immune from" exists, but it doesn't have the right meaning here.
"immune from" means, essentially, that someone/something will never have to deal with some problem in the first place. ("immune to", on the other hand, means that someone/something may well have to deal with the problem, but will be successful in defending itself from the problem.)
for instance:
Corporation X is immune from legal action would mean that it's impossible to take legal action against Corporation X in the first place.
Corporation X is immune to legal action would mean that Corporation X's lawyers are so good that it will never lose a legal case, even though many such cases may be brought against it.

--

regarding these idioms, the good news is that you don't really have to care anymore!
see here:
http://www.manhattangmat.com/blog/index ... -the-gmac/

[agarwalmanoj2000]

Hi Ron,

We use Past perfect "had" for older event among two events in the past. Past perfect "had" is used here in correct choice D, but I do not see two past event.

Ozone reaches high concentrations twelve miles above Earth, where it had long appeared immune to human influence;

Please advise what I am missing here.

In addition, kindly also advise, can we use "had" in simple past tense such as "I had a car" or "had" is used only in past perfect with two events in past.

[RonPurewal]

Hi Ron,

We use Past perfect "had" for older event among two events in the past. Past perfect "had" is used here in correct choice D, but I do not see two past event.

Ozone reaches high concentrations twelve miles above Earth, where it had long appeared immune to human influence;

Please advise what I am missing here.

In addition, kindly also advise, can we use "had" in simple past tense such as "I had a car" or "had" is used only in past perfect with two events in past.

NOTE:
verb tenses are much more difficult and subtle than any other types of sentence errors. if you have not fully mastered the most important types of sentence errors -- parallelism, pronouns, subject-verb agreement, and modifier errors -- then do not yet concern yourself with the finer points of verb tense.

--

now that we've gotten that warning out of the way:

yes, if you use the simplistic interpretation of "the past perfect refers to the first of two events in the past", then you aren't going to be able to figure this one out.
more accurately, the past perfect is used to refer to (a) a past event that was completed by some definite past point in time, (b) or had some sort of tangible impact on a definite past situation, or (c) persisted up until some definite point in the past.
in many sentences, that definite point in the past will be signaled by another action written in the past tense. this is probably the easiest form of the past perfect to understand -- hence the simplistic "rule" above.

however, the definite point in the past does not have to be represented by a past-tense verb; as long as it is clearly implied in the context of the sentence, you are good to go.
in this sentence, the last clause implies the discovery (at some time in the probably-the recent past) that fluorocarbons deplete the ozone layer. that discovery serves adequately as your past-time reference upon which to build the past perfect.

[thanghnvn]

I still don't get the usuage of "HAD" over "HAS", since it says "we have now realized" - That is present, so why can't we say "has appeared" (which means continue till present and now we realized it wasn't the case), whereas "had" would mean it appeared in PAST's PAST....I always get confused in this usage...help?
Thanks.

yeah, i can see how this is tough.

when you say "we have realized", though, this actually means that the realization took place in the PAST. (probably the recent past, but in the past nonetheless.)

here's the fuller deal with the present perfect ("has/have VERBed"):
if you use the present perfect with a POINT EVENT - i.e., an event that OCCURS AT A SINGLE INSTANCE IN TIME (realized, graduated, paid, given birth, scored, etc.) - then the event must have taken place IN THE PAST.
normally this is the quite recent past, but that's not always the case.
think about these:
my brother has obtained three business degrees.
the team has scored 32 points in this quarter.
Russia and the U.S. have sent expeditions to the moon.
these are all point events, and they are all PAST events.
the second is obviously in the very recent past, but the third is an event that happened over forty years ago (but to which we can still refer in the present perfect if it's relevant to the current topic of discussion). the first could be anywhere from a few minutes ago to 60-70 years ago, depending on my brother's age.

notice that, since these are "point" events, it's actually IMPOSSIBLE to refer to them in the present - unless you're narrating them, in the style of a sports announcer ("Demps scores a touchdown!")
so if you see them in the present perfect, they've already happened.

--

verb tenses are easily the toughest aspect of learning any language. hang in there.

GREAT, thank you Ron for this point.
if "have done" show point event, it refers to past event and can go with "had done"
if "have done" shows non point event, if refers to action begin in the past and continue into present and can not go with "had done"

is that right?

can you give an example of "non point event" in which "have done" can not be used with "had done" ??

ton of thank , ron.

[RonPurewal]

GREAT, thank you Ron for this point.
if "have done" show point event, it refers to past event and can go with "had done"
if "have done" shows non point event, if refers to action begin in the past and continue into present and can not go with "had done"

i can't do much better than the examples above.

in general, there's no reason to make the issue this complex -- when you consider verb tenses, just consider them individually.
if you start trying to make formulas for which tenses can go with which other ones, you're going to have issues, because lots of sentences involve more than one point of view.

e.g.
Ray has learned to sew clothes in less time than he had thought it would take before he became good at it.
--> make sure you understand how this sentence works. there are two timeframes. "has learned" is seen from the standpoint of the present, but "had thought" and "became" are presented in the context of the past.

[thanghnvn]

[quote="Anirudh"]Ozone reaches high concentrations twelve miles above Earth, where it// has long appeared that it was immune from// human influence; we have now realized, though, that emissions of industrial chlorofluorocarbons deplete the ozone layer.

A) has long appeared that it was immune from

B) has long appeared to have been immune from

C) has long appeared as being immune to

D) had long appeared immune to

E) had long appeared that it was immune to

from OA D, we learn that "had done" can go with "have done". this is reasonable because past perfect is used to shown an action happening before a point in the past. the past point can be a past action (did) or an action which begin in the past and continue to present or which finish in the past but whose effect connects with present ( have done)

it is seldom explained in grammar books that "had done" can go with "have done" . but this going together is logic and is the acceptable in this question.

do you think so?

[RonPurewal]

those tenses aren't really "going together". they're used for totally separate ideas in separate timeframes; each should be examined individually.

[RAHULS852]

Hi Sage/ Manhattan expert,

I am getting confused with "had" & "has" in same sentence.
As Ron stated that when you say "we have realized", though, this actually means that the realization took place in the PAST. (probably the recent past, but in the past nonetheless.)

Then use of "had" is OK because "has +ed" represents a past event after "had+ed"
D) Ozone reaches high concentrations twelve miles above Earth, where it had long appeared immune to human influence; we have now realized, though, that emissions of industrial chlorofluorocarbons deplete the ozone layer.

in above choice both highlighted portion represent 2 past events.
I put same rule in a MGCAT SC question but got wrong.

Art historians have suggested that Impressionism, with its emphasis on color and form at the expense of exact duplication of detail, had evolved in response to the advent of black-and-white photography, which allowed precise, albeit monochromatic, pictorial reproduction of a landscape

Here "have suggested" also seems to be a point event. Then why use of "had" is wrong in above example ?
Am I missing something ?

Regards,
Rahul Singh

[Sage Pearce-Higgins]

A few notes about present perfect and past perfect may help here.
1. Think of present perfect as a tense that connects the present and the past. It may be that the event is still true 'I've lived in NYC for 2 years.', or that it's recent 'I've just won the competition!', or that we can see the results 'What have you been doing?'. There are several kinds of relationship going on here.
2. Think of past perfect as the past before the past. It's a really useful tense for making the order of past events clear. Compare 'When I arrived, they had eaten dinner.' with 'When I arrived, they ate dinner.' However, if the order is already clear, then we don't need to use it. For example, 'He was crying because he lost his toy.' is totally fine, although 'He was crying because he had lost his toy.' is also fine.
3. Note that the deciding factor is the meaning of the sentence: tenses, like all grammar, exist so that we can communicate effectively. Rules can help us out here, but don't be a slave to a rule if it doesn't fit the situation.

Applying these thoughts to those problems, note that the ozone problem doesn't give you a choice between 'had appeared' and simply 'appeared'. Here, the 'had' emphasizes that the appearing took place before the realization, but I think 'appeared' would be fine also. It's not that common to use past perfect for an event before present perfect. The more common pairing is past perfect and past simple.

As for the second one, the phrase 'Art historians have suggested that Impressionism...' means that some suggested in the past, but the suggestion is still going on. I can't find any other logical relationship between the past and the present for this context. It might as well say, 'Some art historians suggest that Impressionism...'. Consequently, we don't have a second past event to use with the past perfect.

Here "have suggested" also seems to be a point event.

Not sure exactly what you mean by 'point event', but if you mean 'action that took place in the past and is now finished' then we'd need to use the past simple. If we wanted to state that the suggesting took place in the past and is finished now, we'd need to say 'Some art historians once suggested that Impressionism...'.