Q21 - Although the geological record

[sarahhaque]

Could you please explain why answer choice A is correct and answer choice B is wrong?

I chose B, but A looks very similar except that it uses the term "all" (instead of "many" in B)

How important is it to understand the LSAT usage of ALL, MANY, ANY, MOST etc? Or, am I being thrown off by paying too much attention to detail?

Merci!

[ManhattanPrepLSAT1]

Those words are the key to doing well on the LSAT. In fact it's the difference between "all" and "many" that makes answer choice (A) right and (B) wrong.

Let's evaluate the following two arguments...

#1
If Sandy' soccer team was going to win, then all of the players must have played well today. Not all of the players on Sandy's team played well though. Therefore, Sandy's soccer team did not win.

vs.

#2
If Sandy's soccer team was going to win, then some of the players must have played well today. Not all of the players on Sandy's team played well though. Therefore, Sandy's soccer team did not win.

The second argument is not valid, because the argument leaves room for a superstar to carry the team to victory. The first argument, however, is valid. Because in order to win, everyone has to play well - but they didn't.

(A) fills the gap between the evidence and the conclusion.
(B) strengthens the argument, but isn't enough to prove the conclusion.
(C) doesn't bridge the gap to the conclusion about a consistent causal link.
(D) relates the two terms we want connected. But the relationship is backwards. It's similar to the difference between the following.

Suppose the gap is A --> B
The assumption ~A --> ~B wouldn't work out well.

(E) undermines the conclusion. It says that there is no causal link period!

[ManhattanPrepLSAT1]

Let's look at the argument more specifically...

Evidence

Some mass extinctions are not preceded by major meteor impacts. Some major meteor impacts are not followed by mass extinctions.

Conclusion

There is no consistent causal link.

Assumption

1. If some mass extinctions are not preceded by major meteor impacts, then there is no causal link.
2. If some major meteor impacts are not followed by mass extinctions, then there is no causal link.

Contrapositives of each Assumption

1. If there is a consistent causal link, then all mass extinctions would be preceded by major meteor impacts.
2. If there is a consistent causal link, then all major meteor impacts would be followed by mass extinctions.

The correct answer could be either of the stated assumptions or the contrapositives. Answer choice (A) is the contrapositive of the second assumtpion.

[danielalfino]

I guess I confused as to how you've determined the contrapositive of "some" to mean "all." I thought that the opposite of "no[t]" was "all" and "some" and "no[t]" I believe are different.

I'll give an example of my issue.

If some of Sally's friends go to the store, then they will have apples for the picnic."

According to what you're saying the contrapositive would be:
If they don't have any apples for the picnic, then none of Sally's friends went to the store.

However, I figured that the contrapositive would be:
If they don't have any apples for the picnic, then those friends [but not excluding her other friends] went to the store.

I don't mean to keep bothering you with this question, but I guess it gets at the core of the conditional logic. I couldn't find any examples in the strategy guide that dealt with non-absolutes in language. Can you explain why you can rule out Sally's other friends, and thus arrive an an absolute "all" contrapositive for this question?

Thanks...

[ManhattanPrepLSAT1]

It's never a bother to work on the LSAT!

I'll give an example of my issue.

If some of Sally's friends go to the store, then they will have apples for the picnic."

According to what you're saying the contrapositive would be:
If they don't have any apples for the picnic, then none of Sally's friends went to the store.

This is actually correct!

The logical opposite of

All = Not All
Not All = All
Some = None
None = Some

So the contrapostive of

If every child is beautiful, then the world is wonderful.

would be

If the world is not wonderful, then not every child is beautiful.


Here's another example

The contrapositive of

If wealth is a good thing, then good things never cause harm.

would be

If good things sometimes cause harm, then wealth is not a good thing.

(this is actually taken from a real LSAT question)

===========================

Many = some, it does not equal most.

Here are some words that imply "some" statements:

some, many, several, a few, a significant amount, frequently, often, occasionally, sometimes, and not all

Here are some words that imply "most" statements:

most, more than half, a majority, nearly all, usually, typically, and generally

Hope that helps!

[ManhattanPrepLSAT1]

Sorry, I wasn't implying that either...

You should definitely distinguish "some" statements, "most" statements, and "all" statements on the LSAT.

It's just that many = some, it does not equal most.

Here are some words that imply "some" statements:

some, many, several, a few, a significant amount, frequently, often, occasionally, sometimes, and not all

Here are some words that imply "most" statements:

most, more than half, a majority, nearly all, usually, typically, and generally

Hope that helps!

[ManhattanPrepLSAT1]

So since most are not B, can we infer that the remainder is B? (I’m guessing no?)

So while we're at it...

Some A's are B's
Opposite: Some A's are not B's

Same question, Since some A's are not B's can we infer the remainder is B?

Remember that "some" and "most" statements have a floor but no ceiling.

So if you know that most A's are B's, that does not imply that some are not.

Likewise, if you know that some A's are B's, that does not imply that some are not.

Though these are two common mistakes that folks make when working with conditional/quantified logic.

Hope that helps!

[Raiderblue17]

If I may throw in 2 cents to this:

So the author is conceding that some impacts didn't cause extinctions and that some extinctions didn't follow any impacts.

Because of this he/she says that there is not a link involved. So clearly the only way to get the author to accept a link would be that if EVERY impact caused extinction and that every extinction would be preceded by an impact.

I know were going deep into things, but honestly the easy way is to see that the author's assumption is that if its not 100% connected it's not a causal connection.

Thoughts????

[ManhattanPrepLSAT1]

Nice work Raiderblue17!

I'd like to follow up that idea with the possibility that what you just did intuitively, is not so easily done by everyone. I know that conditional logic is also not easy, but it's a tool for some who can't make those connections like you just did so easily.

Additionally, answer choices (A), (B), and (D) might also be tempting for those who see that there's a relationship between having less than a 100% correlation between major meteor impacts and mass extinctions, but who are not certain what exactly that relationship should look like.

Finally, whenever your intuition is sufficient to arrive at the correct answer, take it! No need to convert into massive notational structures, if it's not needed.

[ManhattanPrepLSAT1]

Exactly right Timmy! Just because "many major meteor impacts were not followed by mass extinctions" does not allow us to say that it's not true that "many major meteor impacts were followed by mass extinctions."

Since we cannot say the necessary condition of answer choice (B) is false, we cannot use the contrapositive of it to establish the conclusion.

Nice work Timmy!

[monicajamaluddin]

So I picked D because I saw it like this:

~consistent causal link ---> ~all mass extinctions could have followed major meteor impacts

the contrapositive of that was:

if all mass extinctions followed major meteor impacts ---> consistent causal link

Two questions:

1. what is the logical opposite of not all?
2. is this a mistaken reversal of the answer that we need? (i.e. the sufficient is "consistent causal link" and "mass extinctions following meteor impacts" is the necessary? - whereas I thought mass extinctions was the sufficient and causal link was the necessary)

[timmydoeslsat]

So I picked D because I saw it like this:

~consistent causal link ---> ~all mass extinctions could have followed major meteor impacts

the contrapositive of that was:

if all mass extinctions followed major meteor impacts ---> consistent causal link

Two questions:

1. what is the logical opposite of not all?
2. is this a mistaken reversal of the answer that we need? (i.e. the sufficient is "consistent causal link" and "mass extinctions following meteor impacts" is the necessary? - whereas I thought mass extinctions was the sufficient and causal link was the necessary)

1. The logical opposite of not all = all.

Some = not some (none)
Most = not most (half or less)
All = not all

Each side of the equals indicates the logical opposite. In the logic world, we want the world to be divided in half, where any variable can be placed into 1 of those two groups.

Some people may believe the logical opposite of hot is cold. But it is not, as where would you place lukewarm? The logical opposite of hot is simply not hot. You would place lukewarm in the not hot category.

So the logical opposite of not all is simply all.

As to your second point and your selection of D, we need to look at your framing of the conditional.

You are picking an answer choice that has a sufficient condition of "~causal link"

We want to conclude in the argument "~causal link."

We would want "~causal link" to be a necessary condition.

Which would be the same idea (contrapositive) as having "causal link" as the sufficient condition.

We will never be able to conclude "~causal" from "~causal ---> X"

You are simply stating a requirement of "~causal"....which does not mean we have "~causal."

Notice what A does. It gives us [causal ---> all impacts would be followed by extinctions]

And we know we can negate that necessary condition. We are told in the stimulus the some impacts are not followed by extinctions. This would lead us to the idea of "~causal", which is what we want as our conclusion.

[alana.canfield]

I am a little confused about (A) being correct, because even if (A) were true, it does not guarantee that the geological record would suggest that there is a consistent causal link. It only guarantees that in reality there is a causal link. But the conclusion is about the geological record suggesting a link (which isn't guaranteed in the case of (A) since the geological record can be changed/altered by later events).

Please help! THanks!

[ymcho2013]

so when negating these types of quantifying statements, do you negate the verb, the quantifier, or both??

Which is the correct logical opposition????
1. [quantifier change] All A's are B's <--> NOT ALL A's are B's = some A's are not B's
2. [verb change] All A's are B's <--> All A's are NOT B's = A's can never be B's
3. [both change] All A's are B's <--> NOT ALL A's are NOT B's = some A's are B's

Is it #1?

[timmydoeslsat]

so when negating these types of quantifying statements, do you negate the verb, the quantifier, or both??

Which is the correct logical opposition????
1. [quantifier change] All A's are B's <--> NOT ALL A's are B's = some A's are not B's
2. [verb change] All A's are B's <--> All A's are NOT B's = A's can never be B's
3. [both change] All A's are B's <--> NOT ALL A's are NOT B's = some A's are B's

Is it #1?

It depends on the type of statement you are given.

For instance:

#1: Timmy walks to the store where most neighborhood dogs play.

The modifier in this case is simply used to describe a store. To negate that would not be a logical negation. We would want to negate the action verb of walks.

#2: All people go to the store on Wednesday.

If you negate the verb in this case, you will lose the ability to have a logical negation. To have a logical negation, you want to have a true split in the logical world (2 sides). For instance the logical opposite of black is not black. If you were to say that the logical opposite of black is white, then where would you put gray? Blue, etc.? To have a logical negation, you must be able to put any variable into one of two sides of logic.

So, in the #2 example, we can simply say not all people go to the store on Wedneday.

If you were to negate "All people go to the store on Wednesday" as..."All people do not go to the store on Wednesday"...you will then not have a true logical split.

So you want to always think how can I achieve a true logical split. You will not achieve this by negating an action verb AND a quantifier. That is not correct.

[timmydoeslsat]

I am a little confused about (A) being correct, because even if (A) were true, it does not guarantee that the geological record would suggest that there is a consistent causal link. It only guarantees that in reality there is a causal link. But the conclusion is about the geological record suggesting a link (which isn't guaranteed in the case of (A) since the geological record can be changed/altered by later events).

Please help! THanks!

Answer choice A would guarantee our conclusion of there not being a consistent causal link. The future will not matter in our case.

Answer choice A says:

Consistent Causal link ---> All MI are followed by ME

We know that the necessary condition has been disproven in our evidence.

Thus, there is no way that consistent causal link could take place (contrapositive).

The future will not change the facts of what the past has shown, which is that not all MIs are followed by MEs. This conditional statement in (A) will not be able to affected by future events.

[Athomas87]

I know that this question has been discussed extensively but I'm still really confused.

I have:

(Some) extinctions --> ~ follow known major meteor impacts
(Some) major meteor impacts --> ~ followed by extinctions

Therefore, ~ consistent causal link

I don't know what to do from there and I also don't know how A and B are different.

[ohthatpatrick]

It looks like you're eager to diagram stuff (knowing that Sufficient Assumption DOES want Idea Math), but I would suggest that you only make something conditional if it's conditional.

Are wishy-washy words like "some, many, most, etc." words of CERTAINTY?

They're not conditional triggers.
They're not CONDITIONS / UNIVERSALS / GUARANTEES / REQUIREMENTS

They're just ... facts.


How do you test an answer choice on Sufficient Assumption to know whether it's right?



(got your answer?)


You add it to the premises and see if it PROVES (mathematically) the conclusion.

What does a mathematically airtight logical argument look like?
A is B
B is C
thus, A is C

The important feature here is that the two ideas in the conclusion (A and C) are DEFINED in the evidence.

You CANNOT have an airtight conclusion if there's anything new in the conclusion.

The conclusion here is
"[The Geological Record] suggests [no causal link between meteor / extinction]"

You want to ask yourself, "What, if anything, did the Evidence tell me about each of those symbols?"

[The Geological Record] -
sometimes extinctions happened, even though no meteor had struck the earth
sometimes meteors struck the earth, but no extinction happened.

[no causal link between meteor / extinction] -
Nothing was said about this in the Evidence! This is a totally new idea in the Conclusion.

ANY answer that fails to define this term is completely useless. It would never allow us to create a complete circuit, in which every term in the conclusion has been separately defined and linked to each other.

Specifically, we need an answer to take us
FROM the Evidence, TO the conclusion

It will have to give us a rule that says
IF [stuff from the Evidence is true], THEN [no consistent causal link]

Contrapositives, of course, are fine, since they are identical to the original conditional.
IF [consistent causal link], THEN [stuff from the Evidence is NOT true] is totally cool.

But any time an answer choice on LSAT says "IF [conclusion], ..." it will be wrong.

(A) IF [consistent causal link], THEN [every time a meteor struck, an extinction happened]

Okay, from the Evidence do we know whether [every time a meteor struck, an extinction happened]?

We do. We know that this is a false statement. It is not true that every time a meteor struck, an extinction happened. We were told in the Evidence that sometimes a meteor struck, but there was no extinction.

So (A) works! The Evidence triggers the contrapositive of this rule. Since it's NOT the case that "every meteor strike led to an extinction", there is NOT a consistent causal link.

Conclusion derived.

(B) IF [can be consistently causally linked], THEN [many meteor strikes caused extinctions]

Do we know from the Evidence whether [many meteor strikes caused extinctions]?

We don't. We know that many meteor strikes DIDN'T cause extinctions. That's not the same thing.

For example, we know that MANY U.S. Presidents were not female. Does that tell us that MANY U.S. Presidents were female?

Nope. Eliminate (B), because we can't the Evidence-half of this conditional. (Also, proving two things CAN/CAN'T be causally linked doesn't sound like a match for proving that two things ARE/AREN'T causally linked)

(C) Nothing about "consistent causal link", so completely useless.

(D) This says "IF conclusion", so useless.

(E) This actually weakens the argument.

[ohthatpatrick]

It looks like you're eager to diagram stuff (knowing that Sufficient Assumption DOES want Idea Math), but I would suggest that you only make something conditional if it's conditional.

Are wishy-washy words like "some, many, most, etc." words of CERTAINTY?

They're not conditional triggers.
They're not CONDITIONS / UNIVERSALS / GUARANTEES / REQUIREMENTS

They're just ... facts.


How do you test an answer choice on Sufficient Assumption to know whether it's right?



(got your answer?)


You add it to the premises and see if it PROVES (mathematically) the conclusion.

What does a mathematically airtight logical argument look like?
A is B
B is C
thus, A is C

The important feature here is that the two ideas in the conclusion (A and C) are DEFINED in the evidence.

You CANNOT have an airtight conclusion if there's anything new in the conclusion.

The conclusion here is
"[The Geological Record] suggests [no causal link between meteor / extinction]"

You want to ask yourself, "What, if anything, did the Evidence tell me about each of those symbols?"

[The Geological Record] -
sometimes extinctions happened, even though no meteor had struck the earth
sometimes meteors struck the earth, but no extinction happened.

[no causal link between meteor / extinction] -
Nothing was said about this in the Evidence! This is a totally new idea in the Conclusion.

ANY answer that fails to define this term is completely useless. It would never allow us to create a complete circuit, in which every term in the conclusion has been separately defined and linked to each other.

Specifically, we need an answer to take us
FROM the Evidence, TO the conclusion

IF [stuff in the Evidence we heard is true], THEN [no consistent causal link]

Contrapositives, of course, are fine, since they are identical to the original conditional.
IF [consistent causal link], THEN [stuff in the Evidence we heard is NOT true]

But any time an answer choice on LSAT says "IF [conclusion], ..." it will be wrong.

(A) IF [consistent causal link], THEN [every time a meteor struck, an extinction happened]

Okay, from the Evidence do we know whether [every time a meteor struck, an extinction happened]?

We do. We know that this is a false statement. It is not true that every time a meteor struck, an extinction happened. We were told in the Evidence that sometimes a meteor struck, but there was no extinction.

So (A) works! The Evidence triggers the contrapositive of this rule. Since it's NOT the case that "every meteor strike led to an extinction", there is NOT a consistent causal link.

Conclusion derived.

(B) IF [can be consistently causally linked], THEN [many meteor strikes caused extinctions]

Do we know from the Evidence whether [many meteor strikes caused extinctions]?

We don't. We know that many meteor strikes DIDN'T cause extinctions. That's not the same thing.

For example, we know that MANY U.S. Presidents were not female. Does that tell us that MANY U.S. Presidents were female?

Nope. Eliminate (B), because we can't the Evidence-half of this conditional. (Also, proving two things CAN/CAN'T be causally linked doesn't sound like a match for proving that two things ARE/AREN'T causally linked)

(C) Nothing about "consistent causal link", so completely useless.

(D) This says "IF conclusion", so useless.

(E) This actually weakens the argument.

[SeyoungK790]

Let's look at the argument more specifically...

Evidence

Some mass extinctions are not preceded by major meteor impacts. Some major meteor impacts are not followed by mass extinctions.

Conclusion

There is no consistent causal link.

Assumption

1. If some mass extinctions are not preceded by major meteor impacts, then there is no causal link.
2. If some major meteor impacts are not followed by mass extinctions, then there is no causal link.

Contrapositives of each Assumption

1. If there is a consistent causal link, then all mass extinctions would be preceded by major meteor impacts.
2. If there is a consistent causal link, then all major meteor impacts would be followed by mass extinctions.

The correct answer could be either of the stated assumptions or the contrapositives. Answer choice (A) is the contrapositive of the second assumtpion.

Simple paraphrasing questions.!
While reading your version of “Evidence” (quoted above), I could find the difference of understanding on the stimulus between yours and mine.

I understood the stimulus as below
: many extinctions not following any known mjr. Mt impacts
: Likewise, many “records” of mjr impact seemingly not followed by mass extinction

And I thought the second sentence starting with Likewise is just for confusing readers using the word “record” (As the fact that “record” is different from “actual fact” is one of the commonly used concept in LSAT)
And had a further guess that the answer choice (C) is made within that context.

So my question is...
Why did you simply paraphrase the second sentence merely as a reversed(S and O reversed) but with the same meaning with the prior one without considering the concept of “record” on the sentence?

Did you just overlook or is it intentional?
Thanks in advance,
Seyoung