Q18 - If there are sentient beings

[smiller]

What does the Question Stem tell us?
This is a Sufficient Assumption question. The correct answer choice, if added to the premises, will completely guarantee the truth of the conclusion.

Break down the Stimulus:
Let’s be honest. This is potentially a tough question. Some people might arrive at the correct answer using general, intuitive reasoning, but to fully explain why the correct answer is correct we need to look at the underlying conditional logic.

On the other hand, this isn’t a standard Sufficient Assumption question based on conditional logic, where we predict the correct answer by linking the conditional statements and spotting the missing link in the chain of logic. This “sentient beings” argument contains a few twists.

To have any success at all with this question we first have to identify the argument core—the basic structure of the argument. The first sentence is the conclusion. The second sentence contains two premises, separated by “and.” There aren’t any specific keywords like "because" or "thus" pointing to premises or the conclusion, so we have to determine this through context, by seeing which of the statements appears to support the other.

Once we understand the basic structure of the argument, we can examine the reasoning.

There is an approach to this question that we might call the “Krav Maga” approach (a term I’m borrowing from my esteemed colleague, Gerald McMillan). Two concepts, “beings on other planets” and “at least as intelligent as humans,” are mentioned in the conclusion as well as the premises. “Determining if there are sentient beings on other planets” is unique to the conclusion, while “sending spacecraft to other planets” and “communicating with us” are unique to the premises. To take the Krav Maga approach, I’ll focus on these three unique concepts. I’ll eliminate any answer choices that fail to connect them, look for one that does, and hope for a knockout.

For those wanting a more thorough explanation, here it is:

The conclusion is a conditional statement. Both “if” and “unless” can indicate conditional logic, but in this case, “unless” is the conditional operator. The conclusion is about whether or not we can determine something, and “if there are sentient beings on other planets outside our solar system” is the thing that we are trying to determine. If we recognize “unless” as the conditional indicator, we can express the conclusion as a simple “if-then” statement:

C: able to determine if there are beings —> beings at least as intelligent as humans

(The entire argument is about the near future, and beings on planets outside of our solar system, so we’ll leave those details out for the moment.)

Now let’s look at the premises:

P1: cannot send spacecraft to other planets

P2: beings able to communicate with us —> beings at least as intelligent as humans

For the second premise to support the conclusion, we have to assume:

able to determine if there are beings —> beings able to communicate with us

This missing link would normally be the correct answer to this type of question. But what about the first premise? How does that fit in? As mattsherman pointed out in his explanation, it’s difficult to predict an answer using a strictly formulaic conditional logic approach. This is where we need to step back and take a more general look at the reasoning.

For the first premise to support the conclusion, we have to assume:

cannot send spacecraft to other planets —> not able to determine if there are beings

The contrapositive of this is:

able to determine if there are beings —> can send spacecraft to other planets

For the conclusion to follow logically, we have to consider the assumptions implicit in both of the premises:

able to determine if there are beings —> beings able to communicate with us OR can send spacecraft to other planets

Any prephrase?
If we’ve identified the exact assumption, we’re looking for:

able to determine if there are beings —> beings able to communicate with us OR can send spacecraft to other planets

With the Krav Maga approach, we’re hoping for a knockout by eliminating any answers that fail to connect “able to determine if there are beings” with “communicating” and “spacecraft.”

Correct answer:
The correct answer is (D).

Answer choice analysis:
A) Neither our premises nor our conclusion is about planets other than Earth in our own solar system. This answer choice is irrelevant.

B) Our second premise, and the related assumption, deal strictly with others being capable of communicating with us. Whether they want to or not is irrelevant.

C) This answer choice tells us: beings at least as intelligent as humans —> cannot send spacecraft. It doesn’t connect either premise with the ability to determine if there are sentient beings on other planets, so it’s also irrelevant.

D) This is a rewording of the exact assumption we need. If you’re practicing Krav Maga, this is the only answer choice that contains all three concepts we want.

E) This is a reversal of the second premise. It doesn’t connect either premise with the ability to determine if there are sentient beings on other planets, so it’s irrelevant.

Takeaway/Pattern: There are several ways to choose the correct answer for this question. The best method for you will depend on your strengths and overall goals. The Krav Maga approach isn't always guaranteed to work, but if you're stuck it allows you to at least make an educated guess without spending an excessive amount of time on the question.

#officialexplanation

[bfleisch123]

Tony, I'm going to attempt to give you a helpful reply... hopefully to be added to by one of the teachers...

Look at this conclusion:

"If there are sentient being on planets outside our solar system, we will not be able to determine this anytime in the near future UNLESS some of these beings are at least as intelligent as humans"

Now, this "unless" actually introduces a conditional into the conditional in the conclusion:

If there are sentient beings on planets outside our solar system, we will be able to determine this ONLY IF these beings are at least as intelligent as humans.

So, the argument concludes that the intelligence of these beings is a necessary condition for our knowledge of their existence.

given the fact that this is a necessary condition, in order to properly draw this conclusion, look for the answer that eliminates other alternative methods by which we could obtain knowledge of their existence (because if there are other methods, then we don't truly have a necessary condition)

Look what (d) says: What if we COULD detect a sentient being who cannot communicate with us (i.e. who is not at least as intelligent as we are) by some means OTHER than sending a spacecraft to its planet?

If so, then we cannot reach our conclusion because we'd have determined the presence of sentient beings on planets outside our solar system WITHOUT their being as intelligent as us, and thus their intelligence is not a necessary condition for our knowlege of their existence

Thus, we need assumption (d) to properly draw the conclusion.

Note that answers (a) and (b) are irrelevant, and answers (c) and (e) don't adequately address this problem with the necessary conditon I raised.

I hope this is (a) informative, and (b) correct. If not, somebody please fix it as soon as possible

[ManhattanPrepLSAT1]

Great work Elizabeth! This one is tough... But it definitely is testing conditional logic.

Here's how I see it. My take is slightly different but that's mostly just because sentences do have some interpretation involved. The first sentence is the conclusion - as you've identified, and everything else is evidence. I too see two pieces of evidence for why it's true; first we will not be able to send a spacecraft, and second, that if sentient beings are capable of communicating, then they're at least as intelligent as humans.

~SSC
C --> IH
----------
DE ---> IH

Notation Key: SSC = send spacecraft, C = capable of communicating, IH = intelligent as humans, DE = determine they exist

The beauty with this argument is that it's nearly impossible to predict the correct answer when trying to find the gap.

Here's what answer choice (D) says:

if sentient beings are not capable of communicating then the only way to determine whether or not they exist is to send a spacecraft. Put into notation:

~C ---> (DE ---> SSC)

If I add the premise that we're not going to send a spacecraft

~SSC

we can infer:

~C ---> ~DE

Take the contrapositive

DE ---> C

add the evidence

C ---> IH

and we can infer

DE ---> IH (wow, that's the conclusion of the argument!)

I'd love to hear what others think, and if they see it differently!

[gotomedschool]

Man I had a lot of problems reaching this conclusion by diagramming, I guess I got lucky recognizing because my instincts were telling me that we needed to make some kind of connection between sending a spacecraft and communication.

My question is with this: ~C ---> (DE ---> SSC)



How do you reach this as a diagram and then what effect does ~SSC have on the statement?


I thought i had my formal logic down but I've never seen a statement diagrammed like that before...




The way that I diagrammed is as follows:

D --> (C v S) (D = Detect/Determine; C = Communicate; S = Spacecraft)

Since ~S is given:
D --> C

C --> I (I = Intelligent) (Given)
So:
D --> C --> I
D --> I

[ManhattanPrepLSAT1]

I agree that you're logic works, but where in the stimulus do you get D --> (C v S)?

I've never seen this logic before either. There's been a rash of fairly nasty conditional logic questions lately - think along the lines of "there is a difference between beauty and truth." PT49, S4, Q16"

Here's an analogy: if the rain is falling, then if you have an umbrella, you'll be wet. And suppose I can see that you just came through the door and you're not wet. Then if it's raining outside, you had an umbrella.

Expressing that more formally without getting lost in jargon is pretty tough though. Essentially it's using contrapositive argument structure on the conditional relationship. Maybe the best way to go is to visualize it. And we'll be using substitution here:

The assumption is

~C ---> (DE ---> SSC)

Substituting out the conditional relationship DE --> SSC, given that we know ~SSC, we can infer ~DE. Just substitute this back in to get

~C ---> ~DE.

[ManhattanPrepLSAT1]

I am confused by the last step: how come the parenthesis disappears? it reminds me of the math equation with parenthesis: reverse the plus and minus signs before taking off the parenthesis. Is it a likewise principle?

The reason it disappears is that we're incorporating the information ~SSC into the conditional relationship

~C ---> (DE ---> SSC)

Since we know ~SSC, we can state the portion DE ---> SSC as the inference of that claim and ~SSC

DE ---> SSC
~SSC

therefore

~DE

So substituting ~DE back in for DE ---> SSC, we get

~C ---> ~DE

So what does this say in English? If a sentient being cannot communicate with us, then we're not going to detect their existence. How do we know that? Because if a sentient being cannot communicate with us, then if we're going detect their existence, then we'll have to send a spacecraft. But we're not capable of sending a spacecraft anytime in the near future.

Does that answer your question irene122?

[sumukh09]

Here's how I saw it

Premise 1: ~ send spacecraft
Premise 2: Sentient being CC ---> as intelligent as humans

Conclusion: Determine ---> as intelligent as humans

Sentient being CC = Sentient being capable of communicating

the gap would be: ~send spacecraft ---> Sentient being CC

D gives us the contrapositive

ie) ~Sentient being CC ---> Send Spacecraft

Is this reasoning correct? I don't think it is because "determine" isn't accounted for at all in the assumption/gap.

[hyewonkim89]

Great work Elizabeth! This one is tough... But it definitely is testing conditional logic.

Here's how I see it. My take is slightly different but that's mostly just because sentences do have some interpretation involved. The first sentence is the conclusion - as you've identified, and everything else is evidence. I too see two pieces of evidence for why it's true; first we will not be able to send a spacecraft, and second, that if sentient beings are capable of communicating, then they're at least as intelligent as humans.

~SSC
C --> IH
----------
DE ---> IH

Notation Key: SSC = send spacecraft, C = capable of communicating, IH = intelligent as humans, DE = determine they exist

The beauty with this argument is that it's nearly impossible to predict the correct answer when trying to find the gap.

Here's what answer choice (D) says:

if sentient beings are not capable of communicating then the only way to determine whether or not they exist is to send a spacecraft. Put into notation:

~C ---> (DE ---> SSC)

If I add the premise that we're not going to send a spacecraft

~SSC

we can infer:

~C ---> ~DE

Take the contrapositive

DE ---> C

add the evidence

C ---> IH

and we can infer

DE ---> IH (wow, that's the conclusion of the argument!)

I'd love to hear what others think, and if they see it differently!

This was extremely helpful for me to see why (D) is the correct answer.

But I still can't get over (C) completely.

While I was writing this post, I think I realized why (C) is the wrong answer.

(C) never states sentient beings or planets "outside our solar system" as the stimulus does. So what if there is a sentient being on another planet INSIDE OUR SOLAR SYSTEM? We CAN'T infer anything about our ability/inability to send spacecraft to that planet that's not specified as being outside our solar system.

Am I understanding this correctly?

Any help would be appreciated!

[ptewarie]

All these explanations work but, frankly, overcomplicate the question WAY more than is warranted. Whenever I see long, complex formal logic statements I cringe because they take unnecessarily long and unless you have a lot of time left, they will hold you back from finishing other problems.

This is how I solved it:

Evidence:
1. We cannot send spacecrafts outside solar system
2. Sentient beings could only directly communicate with us by being at least as intelligent

Thus,

We can find out if there are sentient beings only if some them are as intelligent as us.

So basically the author says that there are only two ways of finding out if there are sentient beings
1) by direct communication
2) by sending a spacecraft
Since he thinks its going to be unlikely that we can send an spacecraft, he says the only way of finding out is through communication

So he is assuming, there are ONLY THOSE TWO options available.
( this would also make a classic "flaw" question).

D nails this perfectly by noting that if they dont communicate with us , then there the only one way of finding out about them: send the spacecraft.

That's it, move on.

if you didn't see this, you could have used the "denial test".
If you deny answer choice D, you get :

"if a SB on another planet cannot communicate with us, then there ARE other ways to detect is existence instead of sending a spacecraft"


Well this would invalidate the argument completely because it would mean that the conclusion that :
" determine SB on planets ONLY if as intelligent" would no longer hold.

It would mean that we could determine SB on planets despite NOT as intelligent as us and not being able to send spaceship.


For LSAT geeks, remember this:

Whenever you see formal logic in the conclusion of an assumption question, you have to prove that the sufficient cannot occur without the necessary occurring

For everyone else,
when you see two sufficient conditions proven by the author and the author claims that one does not occur so the other sufficient one must occur for the necessary to occur- note the "assumption" is that ONLY THOSE TWO factors are sufficient in allowing the necessary to occur.

[timsportschuetz]

I would like to add my two cents regarding the above explanations since they all seem to miss a crucial test-taking strategy that lends itself well on tough questions such as these!

This is a SUFFICIENT ASSUMPTION question! Firstly, the question is extremely convoluted and complicated (and, I can almost bet that the vast majority have NO idea what they read after the initial read-through). Whenever I see a question such as this, I do the following: Find the UNIQUE phrase and/or word in the argument!!!

Notice how the only unique terms are: Communicating and Sending a spacecraft! Look for an answer choice that has these elements present and immediately and confidently cross out the ones that do not! That leaves us with (B), (C), (D), and (E). I know... pretty disheartening at this point! However, keep in mind that you only spent roughly 20 seconds thus far and you have already eliminated one wrong answer choice. Then, analyse the details of each answer choice:
(B) "Want to communicate" - who the hell cares? Eliminate!
(C) Firstly, where is the unique term "communicate". Secondly, where is the key discussion of "existence" in this answer choice? I wasn't confident at this point and kept it for now. Move on.
(D) OK! This one is a great match! It has both the unique terms present AND is categorical in its language (which is a good indicator in sufficient assumption question answers). Definitely keep!
(E) Again, this is missing the key unique phrase "spacecraft"! Keep for now.

I am down to (C), (D), and (E) at this point. Furthermore, I am already super confident that ONLY (D) has BOTH unique terms present. At this point, I chose not to waste more precious time on an extremely tough question (you have to weigh your odds! You are likely to miss an extremely tough/unusual question... so, spending 3 minutes on such a question AND earning NO points for the time spent is simply ludicrous this late in the section!) and chose (D). This question took me roughly 50 seconds to solve...

I would like to stress that this method is key to a lot of the questions on the LSAT! Always identify scope shifts and/or unique terms or phrases. It is EXTREMELY LIKELY that these terms need to be somehow related! Also, diagramming such a question will waste tons of precious time and energy... especially when you have spent considerable effort on attempting to solve this question and realize that you are not confident at all in choosing the correct answer choice. There are usually one or two questions per test for which I utilize the above... Use the convoluted and extremely tough question stimuli to your advantage! You HAVE to realize that test-writers will know that the vast majority of test takers will have a tough time understanding the argument... therefore, tough questions usually lend themselves well to spotting wrong answer choices.

[royamotazedi]

Can someone please expand on why exactly C is incorrect?

Is C restating a premise? We're already told that "we won't be able to send spacecraft to planets outside our solar systems anytime in the near future" so is C just saying the same thing? When I negate it, "Even if there is a sentient being on another planet that is as intelligent as humans are, it's not necessarily the case that we won't be able to send spacecraft to the being's planet in the near future" it seems to me to hurt the argument but maybe not so much because the argument has already eliminated the possibility of sending spacecraft there.

Many thanks in advance for any assistance! These forums have been essential in my studying prep.

[einuoa]

Can someone please expand on why exactly C is incorrect?

Is C restating a premise? We're already told that "we won't be able to send spacecraft to planets outside our solar systems anytime in the near future" so is C just saying the same thing? When I negate it, "Even if there is a sentient being on another planet that is as intelligent as humans are, it's not necessarily the case that we won't be able to send spacecraft to the being's planet in the near future" it seems to me to hurt the argument but maybe not so much because the argument has already eliminated the possibility of sending spacecraft there.

Many thanks in advance for any assistance! These forums have been essential in my studying prep.

I don't think C is necessarily restating the premise, but linking together the two options for determining the existence of sentient beings. The stimulus says that there are only these two options, communicating or send a space craft, if not one then the other.

But C is saying that if it's one, then it's not the other. But couldn't you have both? Sentient beings on another planet as intelligent as humans are could communicate with us, and we can send a space craft there in the future as well.
Consider this analogy.

To get an A in English this semester, I have to get an A on either the paper or the test. (The stimulus in the question is saying, if I don't get the A on the paper then I have to get the A on the test to get an A in English.)

Choice C is saying that If I get an A on the paper then I probably didn't get an A on the test. What if I got an A on both? The stimulus doesn't discount that, but just states that the two options can't both be false for the conclusion to be true, but both options can be true for the conclusion to be true.

Hope that helps!

[Youngstar2028]

Okay let me add my 2 cents even though a lot has been said already

Question 18 has 2 premises and 1 conclusion

premise 1: we will not be able to send spacecraft to planets outside our solar system anytime in the near future

premise 2: any sentient being outside of our solar system capable of communicating with us would have to be at least as intelligent as we are

conclusion: (rephrased for simplicity) we are able to determine sentient beings in the near future ONLY IF these beings are at least as intelligent as humans.

Notice that the argument has precluded any other way of detecting sentient beings except the two ways (premise 1 and premise 2) stated. In fact, the author has eliminated one way already (premise 1) leaving only premise 2.

For the conclusion to follow, we have to in fact know that the two ways are the only ways.

Answer choice (D) says these are the only two ways.

Remember that when practicing with questions like this, always actively look for the answer that protects the conclusion otherwise unnecessary time will be spent on inconsequential answers, that's if you don't get confused first.

[adam.j.brown1]

QUICK SOLUTION PROPOSAL

There seem to be some pretty technical responses to this question, which are great for brute force, but not for saving time in answering the question quickly. I took a more general approach that skipped the conditional logic untangling and focused more on the justify/assumption task. Maybe this alternate method helps some folks out.

As long as we can identify what's different between the conclusion and the premises, this question becomes quick work:

CONCLUSION
"If there are sentient beings on planets outside our solar system, we will not be able to determine this anytime in the near future unless some of those beings are at least as intelligent as humans."

re-written: If we're to determine if there is sentient life out there, some of those beings need to be as intelligent as us.

PREMISE 1
"We will not be able to send spacecraft outside our solar system anytime in the near future, "

PREMISE 2
"and any sentient being on another planet capable of communicating with us anytime in the near future would have to be at least as intelligent as we are."

Because this is an assumption question - we're looking to fix a disconnect between the conclusion and the premises. With this in mind, I eliminated any answer choices that already had shared elements in the stimulus. In this case: "as intelligent as humans / us." This immediately eliminates answer choices B, C and E. Answer choice A seemed like an absolute assertion to me, and as such, out of scope. This leaves us with D.

D connects the non-shared ideas in the stimulus perfectly (which is why this could be classified as a Justify question).
P1: communication
C: detection of existence
P2: send spacecraft

[AnnaC659]

Hi, I read the official explanation above but I am now even more confused then before.

I originally chose E but upon review chose B.. sadly, none of which are correct answers.

Can anyone please go through this one more time, perhaps in a different/simpler approach than the official explanation above?

Thank you!

[ohthatpatrick]

Sufficient Assumption is question that asks us,
"Which answer choice, if we add it to the evidence we already have, will allow us to mathematically derive the conclusion?"

So, naturally our first job is find the conclusion.

There are usually structural words that help you find the conclusion on Sufficient Assumption. Here, the only one they provided was "and".

How does "and" work? It connects two premises (or two ideas that function in a similar way). Given that this is the structure of this paragraph ....
CLAIM 1. CLAIM 2 and CLAIM 3.
... the conclusion has to be claim 1.

So we're trying to prove the first sentence. The first sentence is a nested conditional:
If X, then Y, unless Z.

If you don't already know how to handle that, grab a flashcard so that you can quiz yourself on this later.
X and ~Z --> Y.

CONCLUSION:
If there are sentient beings outside the solar system and none of them are as intelligent as humans, then we won't have any way soon of knowing that they exist.

Okay, so our job is essentially to prove that we'll have no way of knowing whether certain aliens exist. Do we get any conditional rules that say
"if such and such is true, then there's no way to determine whether they exist" ?

We don't.

Thus, the correct answer will have to supply us with a rule that says
"if such and such is true, there's no way to determine whether ___ exists"

If we scanned the answers looking for that, we would only really have (D) to consider. It's the only answer choice giving us a rule about determining whether something exists (it speaks of whether we could "detect existence", which is equivalent to "determine whether something exists").

Knowing the NEW GUY IN THE CONCLUSION shortcut for Sufficient Assumption could pay some big dividends here, since we'd be led straight to (D).

However, typically the NEW GUY shortcut eliminates SOME wrong answers, but not all of them. So let's practice going farther with our stimulus thinking so that we can know better what we want our correct answer to say / do.

We're trying to prove that humans won't have any way soon of detecting whether certain aliens (less intelligent than us / out of our solar system) exist.

We didn't get any rule for proving whether we could / couldn't soon detect whether something exists. But maybe we were provided with some information about these certain aliens?

YES - we know two things about these certain aliens ...
1. aren't as intelligent as us? That means they can't communicate with us soon.
2. outside our solar system? That means we can't send spacecraft soon.

So we could prephrase the correct answer by thinking,
"If aliens can't communicate with us and can't be reached by spacecraft, then we can't determine whether they exist".

(D) isn't worded exactly that way, but it accomplishes the same meaning.
If they can't communicate with us (they can't) ... then the only hope of detecting their existence is spacecraft (which is not an option).

So detecting their existence is hopeless. We did it! We proved the conclusion.

[nanl32]

Hi Patrick,

Thank you for your explanation!

But I am still a little confused. The conclusion is a conditional. How to deal with the " If part" of the conclusion? You said "we are provided with some information about these certain aliens". But " the two thins"(less intelligent than as/ out of our solar system) you mentioned are present in conclusion rather than in premises.

Or can it be interpreted that the "truly conclusion" is that humans won't have any way soon of detecting whether certain aliens exist, just ignoring the "if part"?

[ohthatpatrick]

"out of solar system" and "less intelligent" show up in the premises as well as in the conclusion.

Maybe it would help for you to just think about the argument, including the correct answer, that leads us to being able to derive the conclusion:

Prem: Aliens less intelligent than us wouldn't be capable of communicating with us.
(D): If an alien can't communicate with us, then we can only detect its existence by sending a spacecraft there.
Prem: We can't send a spacecraft beyond the solar system any time soon.

CONC: so if there are aliens beyond the solar system that are less intelligent than us, then we won't be able to detect their existence any time soon.