This is a simple question but is the only difference between necessary and sufficient assumption is that the sufficient is stronger than the necessary? While you're still identifying the gap in the argument, and then tailoring the answer to fill that gap, the sufficient guarantees the conclusion, whereas the necessary is just the baseline of what should be true to make the conclusion true?
@AnnaliseRamirez Kind of, but keep in mind that the same assumption can be both sufficient to make the argument valid but also necessary to make the argument valid. So it's not that sufficient assumptions are stronger; just that they can be stronger than necessary. Whereas necessary assumptions can't be stronger than the argument needs.
@AnnaliseRamirez Sufficient assumptions tend to be stronger because if they are true, then the claim must be true. There is no set intersection. Like I might claim:
This sundae is delicious because it includes Maraschino cherries.
The sufficient assumption can't be "Desserts including Maraschino cherries can be delicious" because that doesn't ensure that the sundae is delicious. It just opens up the possibility that it can be delicious, which is necessary but not sufficient to arrive at our conclusion. A sufficient assumption here would be "All desserts that include Maraschino cherries are delicious". This ensures that the sundae is delicious because it includes the cherries. That "all" statement is strong enough on its own (i.e., it is sufficient) to ensure that the claim is valid.
Going back to the less strong claim: Imagine if we negate that weaker claim. Desserts including Maraschino cherries cannot be delicious. Now it's clearer that the assumption that Maraschino cherries can be part of delicious desserts was necessary to the argument.
This is an artifact of how negation in argumentation works. The negation of "some" is "not some", or "none". If we're trying to claim that a member of one set (a sundae with Maraschino cherries) is also a member of a target set (delicious desserts), then there must be some intersection between the two sets. If there is no intersection between the two sets, then the claim is invalid. So a premise or assumption that the sets intersect (Desserts including Maraschino cherries can be delicious) is necessary in order to validly reach the conclusion.
The negation of "all" is "not all". If we're trying to claim that membership of a subset (desserts with Maraschino cherries) is sufficient for membership of a target set (delicious desserts), we need that subset to be fully subsumed by the target set (all desserts that include Maraschino cherries are delicious). If that subset is actually an intersecting set instead and some members of that subset lie outside of the superset (i.e., "not all" or "some" or even "most" desserts that include Maraschino cherries are delicious), then being a member of that subset is not sufficient to validly conclude membership of the target set.
This is not foolproof, however. Sometimes there are multiple different conditions we need to keep track of and that can be distracting or complicate the argument. But I try to hold on to these first principles to direct my reasoning.
@BriannaZuniga That's right. If the negation weakens the argument, that proves the author had to assume that statement. (Because if it weren't true, then the conclusion wouldn't make sense from the premise.)
Q6 and Q7 were so easy for me, but I struggled with a couple in the middle. Maybe the science questions just throw me off, even though the concepts are the same.
@DarcyOvalles I think I got this question wrong because I read the conclusion as a conditional conclusion (no major alterations --> no complex reasoning), rather than separating the premise and the actual and finding the missing link (NA).
@DouglasSmith I found the conditional statement to be complex reasoning sufficient for changes in behaviour. Ie changes in behaviour are necessary for complex reasoning. And that makes the most sense with our answer which is "if complex reasoning (sufficient) then behaviour changes possible (necessary)".
Like any other Fast Track lessons, thank you for this! Questions 1-6 were straightforward to me, but not 7. I try to answer them as though timed before Kevin goes through it, so the weakness in ACs in 7th made me think about and look at it more closely compared to the other questions.
Question 4 is problematic. Answer choice B may be the strongest answer, but E could also be viewed as necessary. We don't know how old Macaques are (the time period may only encapsulate one generation), so if the author is trying to prove that they can adopt and PASS ON new patterns of social behavior, this seems to heavily point towards passing the behavior to subsequent generations. If that is the case, it is necessary that the pattern will persist over several generations if the case is being used to prove the conclusion by the author. B is stronger due to ambiguity around what "pass on" and "several generations" means, but otherwise it is VERY close.
When answering these necessary assumption questions, would you suggest beginning with negating the answers to determine if it may be the answer, or only negating those which seem to be relevant or correct after eliminating incorrect answers?
@LindsayGeer Definitely the second. Most answers we should get rid of because we recognize that they're irrelevant. Then the ones that we're not sure about we can try negating.
Can somebody explain why answer A on #2 was wrong? I know Kevin said we could find more about that in a different video but I don't know where to find that video.
@charlenehansen I am also struggling as to how A was wrong, and how to be able to answer these questions quickly with not choosing the reverse of the correct answer.
@charlenehansen I think its because A is too broad with "animals" whereas the prompt specified "these animals" in relation to reptiles, which D specifies. A could be correct if the wording/implication of D was changed.
@Aletariel the stimulus states that since they can not make major alterations then they MUST be incapable of complex reasoning. This means that the capability of making major alterations is necessary for the capability of complex reasoning.
alterations -> reasoning
Answer A states that the only way they could be capable of major changes is if they were capable of complex reasoning.
reasoning -> alterations
And that is why Kevin said that A was backwards.
I think I struggled so much with this question because I needed to draw the subset/superset picture and didn't. I've also found myself to struggle with questions about topics related to my undergrad courses like this one.
@charlenehansen I thought that only if conditionals could be diagrammed like A <-> B. I interpreted Answer A to mean major changes <-> complex reasoning. I'm struggling to understand how the complex reasoning is the NC in Answer A and not in Answer D.
@AmyDoval I've run into the same problem, and for me, it has helped to try and differentiate between the language "if and only if" and just "only if." Annoyingly, "only if" is the same part as "then" in a one way conditional. So, "if A, then B" and "A only if B" are equivalent statements.
A good example might be:
if [one is in Texas] then [one is in the United States]
which would be functionally equivalent to:
[one is in Texas] only if [one is in the United States]
the above examples would not be equivalent to the statement
[one is in Texas] if and only if [one is in the United States]
Because biconditional statements, (<->) are always fully reversible while maintaining their meanings, to reverse this would be to say:
[one is in the United States] if and only if [one is in Texas]
which simply isn't true.
In applying this logic to question 2, we can see that the premise we are targeting says something along the lines of:
major changes --> complex reasoning
so when we take the contrapositive, we need an assumption that fits the structure:
complex reasoning --> major changes
Answer A (because it uses the language "only if") is still structured to say "major changes --> complex reasoning" but this functionally says "all animals that can make major changes are capable of complex reasoning" leaving room for other animals that are not capable of making major changes to still be capable of complex reasoning. The statement can only be negated if an animal is capable of making changes but NOT capable of complex thought, and because the author states the premise that reptiles are not capable of making changes, the statement ends up being irrelevant.
Hi Kevin! This was super super helpful. I've been so stuck with Necessary Assumptions lately. But some takeaways I took from your crash course were that:
Asking: would the author agree with this answer. I think this is a good approach than just the MBT test. MBT test is similar, but it's quite vague. Having a guiding question is easier for me to take and apply to the real test.
Negation test. After watching your crash course, I realised that I haven't been applying negation test in the best and simplest way. I learned from your video that negating Quantifiers and removing NOT is an easier approach than whatever the heck I was doing.
Language shouldn't be the deciding factor. I've been attending the live classes and a lot of people go through the answer choice and say "only", "always", etc is too strong. But as you say, language strength isn't a helpful way to approach analyzing the AC. We can see use language strength to see if Author supports the AC, but language strength alone shouldn't be a deciding factor.
This was super super helpful, and I'm hoping I can take these takeaways and use them to improve my accuracy on these!
This helped me really process what I was doing wrong. Correct me if I'm wrong but when doing Sufficient assumption questions, the new concept is in the conclusion and not in the premises. Meanwhile Necessary assumption questions have "new concepts" but here it's known as the "missing piece" and it's found in the premises not in the conclusion
Amazing lesson. I have struggled a lot with NA questions on recent prep tests, but I felt the Core Curriculum was not really what I needed to re-review. This high level summary was perfect. After reviewing this video and taking notes on the main lessons, I think I was able to identify the key areas I was struggling with. Thank you very much!
I ended up picking D because I knew A was reversed. But the word "sometimes" in D threw me off. If making major changes in their behavior is the necessary condition, doesn't the word sometimes make the answer wrong?
@praksesprepper The premise tells us that reptiles are "incapable" of making major changes in behavior. So the link the author assumes is:
incapable of major changes --> incapable of complex reasoning
contrapositive:
capable of complex reasoning --> capable of major changes
D says sometimes because it's matching up to "capable of major changes". In fact D would be wrong if it said "if reptiles were capable, they would always make major changes" because that's too extreme for the actual line of reasoning.
i always confuse sufficient and necessary. i can always narrow it down to 2 possible answers, yet i tend to choose the one that confuses necessary and sufficient. i dont know how to correct this ugh.
@Ssss Return to the Conditional and Set Logic module -- this is probably the source of a lot of your confusion with sufficient and necessary conditions. It can take a lot of practice to get fluent in these concepts.
@Ssss One thing that helped me when I was first starting with conditional logic is to map out every single question and answer that uses conditionals.
I would take a practice question under normal time control (ie try to answer efficiently), then on blind review, I would diagram the question, understand from that diagram what piece was missing that I should be looking for, then diagram all the answers, and understand why the wrong answers didn't fit/interact with the diagram of the question.
This will help you actively expose yourself to sufficiency/necessity, and you will soon be able to "diagram" mentally and see the missing pieces without having to put pen to paper.
for some reason I do better on necessary assumption question than sufficient assumption questions... I'm just so confused on why necessary assumption makes more sense to me than sufficient. I think I view them as the same? is there a specific difference between them that others have noticed?
Such a helpful explainer with great take-away tips; thank you Kevin!
One question: in Question 4 re: macaque monkeys, you mentioned that B is easy to negate because you can just take away the "not" in a sentence that is "Subject is not Predicate", ie negated AC becomes "Subject is Predicate".
Is it it always okay to do that, or are there some parameters around when we can do that? (for example, if the Subject is singular not plural)?
Or are there cases where just dropping the "not" may not work how we need it to for a negation test? Ie, where taking a way the "not" needs to be a "some" instead of "all" relationship? ie, "Subject is not Predicate" needs to be negated to "Subject is SOMETIMES Predicate" or "Some Subject(s) are Predicate" to properly evaluate whether it breaks the argument?
Is it wrong to assume in Q2 AC A is too broad as well because it says "Animals" As opposed to the reptile in question? It feels like a subtlety that the argument is not as broad as AC A makes it out to be?
@Danny_F I think this is debatable. The "reptile" aspect of the argument didn't seem to be play a role in the logic, so arguably the author's assumption isn't narrowed to reptiles alone.
@e.wimoine The second half of the Logic of Intersecting Sets module discusses this! But you bring up a good point; maybe there should be a Fast Track - Negation
@Kevin_Lin yes, a Fast Track - Negation video would be super helpful! Especially where negation leads to double negatives; how we can read them in a way that makes more sense.
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These fast track videos have been super helpful. Thank you Kevin.
Kevin, you are my Moses macaque of the LSAT.
@TBlack05 LOL I will follow him into the hot springs of this exam I sure will
This is a simple question but is the only difference between necessary and sufficient assumption is that the sufficient is stronger than the necessary? While you're still identifying the gap in the argument, and then tailoring the answer to fill that gap, the sufficient guarantees the conclusion, whereas the necessary is just the baseline of what should be true to make the conclusion true?
@AnnaliseRamirez Kind of, but keep in mind that the same assumption can be both sufficient to make the argument valid but also necessary to make the argument valid. So it's not that sufficient assumptions are stronger; just that they can be stronger than necessary. Whereas necessary assumptions can't be stronger than the argument needs.
@AnnaliseRamirez Sufficient assumptions tend to be stronger because if they are true, then the claim must be true. There is no set intersection. Like I might claim:
This sundae is delicious because it includes Maraschino cherries.
The sufficient assumption can't be "Desserts including Maraschino cherries can be delicious" because that doesn't ensure that the sundae is delicious. It just opens up the possibility that it can be delicious, which is necessary but not sufficient to arrive at our conclusion. A sufficient assumption here would be "All desserts that include Maraschino cherries are delicious". This ensures that the sundae is delicious because it includes the cherries. That "all" statement is strong enough on its own (i.e., it is sufficient) to ensure that the claim is valid.
Going back to the less strong claim: Imagine if we negate that weaker claim. Desserts including Maraschino cherries cannot be delicious. Now it's clearer that the assumption that Maraschino cherries can be part of delicious desserts was necessary to the argument.
This is an artifact of how negation in argumentation works. The negation of "some" is "not some", or "none". If we're trying to claim that a member of one set (a sundae with Maraschino cherries) is also a member of a target set (delicious desserts), then there must be some intersection between the two sets. If there is no intersection between the two sets, then the claim is invalid. So a premise or assumption that the sets intersect (Desserts including Maraschino cherries can be delicious) is necessary in order to validly reach the conclusion.
The negation of "all" is "not all". If we're trying to claim that membership of a subset (desserts with Maraschino cherries) is sufficient for membership of a target set (delicious desserts), we need that subset to be fully subsumed by the target set (all desserts that include Maraschino cherries are delicious). If that subset is actually an intersecting set instead and some members of that subset lie outside of the superset (i.e., "not all" or "some" or even "most" desserts that include Maraschino cherries are delicious), then being a member of that subset is not sufficient to validly conclude membership of the target set.
This is not foolproof, however. Sometimes there are multiple different conditions we need to keep track of and that can be distracting or complicate the argument. But I try to hold on to these first principles to direct my reasoning.
so if you negate the answer and it weakens the argument, then it is the correct answer?
@BriannaZuniga That's right. If the negation weakens the argument, that proves the author had to assume that statement. (Because if it weren't true, then the conclusion wouldn't make sense from the premise.)
Q6 and Q7 were so easy for me, but I struggled with a couple in the middle. Maybe the science questions just throw me off, even though the concepts are the same.
To me, it sounds like you are restating the argument in Q2, and then that is your answer. But I do not understand why.
The argument states: Incapable of making major alterations --> Incapable of complex reasoning
The answer is the contrapositive: Capable of complex reasoning --> capable of making major changes
That is the same statement.
@DarcyOvalles I think I got this question wrong because I read the conclusion as a conditional conclusion (no major alterations --> no complex reasoning), rather than separating the premise and the actual and finding the missing link (NA).
@DarcyOvalles Not an expert, but this is how I see it.
I think he wants to keep it conditional and the contra positive will be the correct answer.
Stim:
Incapable of making major alterations --> Incapable of complex reasoning
Contra:
Capable of Complex Reasoning --> Capable of Making major alterations.
If you negate the Contra, the conditional reasoning fails (hence the argument falls apart).
@DouglasSmith I got the Negation wrong and I removed that from the first response. the negation explanation starts at 18:55.
@DouglasSmith I found the conditional statement to be complex reasoning sufficient for changes in behaviour. Ie changes in behaviour are necessary for complex reasoning. And that makes the most sense with our answer which is "if complex reasoning (sufficient) then behaviour changes possible (necessary)".
Like any other Fast Track lessons, thank you for this! Questions 1-6 were straightforward to me, but not 7. I try to answer them as though timed before Kevin goes through it, so the weakness in ACs in 7th made me think about and look at it more closely compared to the other questions.
Question 4 is problematic. Answer choice B may be the strongest answer, but E could also be viewed as necessary. We don't know how old Macaques are (the time period may only encapsulate one generation), so if the author is trying to prove that they can adopt and PASS ON new patterns of social behavior, this seems to heavily point towards passing the behavior to subsequent generations. If that is the case, it is necessary that the pattern will persist over several generations if the case is being used to prove the conclusion by the author. B is stronger due to ambiguity around what "pass on" and "several generations" means, but otherwise it is VERY close.
question 6 really got me for some reason. i could have sworn it was d. super subtle
When answering these necessary assumption questions, would you suggest beginning with negating the answers to determine if it may be the answer, or only negating those which seem to be relevant or correct after eliminating incorrect answers?
@LindsayGeer Definitely the second. Most answers we should get rid of because we recognize that they're irrelevant. Then the ones that we're not sure about we can try negating.
Can somebody explain why answer A on #2 was wrong? I know Kevin said we could find more about that in a different video but I don't know where to find that video.
@charlenehansen I am also struggling as to how A was wrong, and how to be able to answer these questions quickly with not choosing the reverse of the correct answer.
@charlenehansen Have you reviewed the Conditional Logic Module in Foundations lessons?
@Kevin_Lin I recently reviewed "Conditional Logic in 30 Minutes".
@charlenehansen I think its because A is too broad with "animals" whereas the prompt specified "these animals" in relation to reptiles, which D specifies. A could be correct if the wording/implication of D was changed.
@Aletariel the stimulus states that since they can not make major alterations then they MUST be incapable of complex reasoning. This means that the capability of making major alterations is necessary for the capability of complex reasoning.
alterations -> reasoning
Answer A states that the only way they could be capable of major changes is if they were capable of complex reasoning.
reasoning -> alterations
And that is why Kevin said that A was backwards.
I think I struggled so much with this question because I needed to draw the subset/superset picture and didn't. I've also found myself to struggle with questions about topics related to my undergrad courses like this one.
@charlenehansen I thought that only if conditionals could be diagrammed like A <-> B. I interpreted Answer A to mean major changes <-> complex reasoning. I'm struggling to understand how the complex reasoning is the NC in Answer A and not in Answer D.
@AmyDoval I've run into the same problem, and for me, it has helped to try and differentiate between the language "if and only if" and just "only if." Annoyingly, "only if" is the same part as "then" in a one way conditional. So, "if A, then B" and "A only if B" are equivalent statements.
A good example might be:
if [one is in Texas] then [one is in the United States]
which would be functionally equivalent to:
[one is in Texas] only if [one is in the United States]
the above examples would not be equivalent to the statement
[one is in Texas] if and only if [one is in the United States]
Because biconditional statements, (<->) are always fully reversible while maintaining their meanings, to reverse this would be to say:
[one is in the United States] if and only if [one is in Texas]
which simply isn't true.
In applying this logic to question 2, we can see that the premise we are targeting says something along the lines of:
major changes-->complex reasoningso when we take the contrapositive, we need an assumption that fits the structure:
complex reasoning --> major changes
Answer A (because it uses the language "only if") is still structured to say "major changes --> complex reasoning" but this functionally says "all animals that can make major changes are capable of complex reasoning" leaving room for other animals that are not capable of making major changes to still be capable of complex reasoning. The statement can only be negated if an animal is capable of making changes but NOT capable of complex thought, and because the author states the premise that reptiles are not capable of making changes, the statement ends up being irrelevant.
@SierraSilversmith414 This just clicked. Thank you so much!!!!
Hi Kevin! This was super super helpful. I've been so stuck with Necessary Assumptions lately. But some takeaways I took from your crash course were that:
Asking: would the author agree with this answer. I think this is a good approach than just the MBT test. MBT test is similar, but it's quite vague. Having a guiding question is easier for me to take and apply to the real test.
Negation test. After watching your crash course, I realised that I haven't been applying negation test in the best and simplest way. I learned from your video that negating Quantifiers and removing NOT is an easier approach than whatever the heck I was doing.
Language shouldn't be the deciding factor. I've been attending the live classes and a lot of people go through the answer choice and say "only", "always", etc is too strong. But as you say, language strength isn't a helpful way to approach analyzing the AC. We can see use language strength to see if Author supports the AC, but language strength alone shouldn't be a deciding factor.
This was super super helpful, and I'm hoping I can take these takeaways and use them to improve my accuracy on these!
This helped me really process what I was doing wrong. Correct me if I'm wrong but when doing Sufficient assumption questions, the new concept is in the conclusion and not in the premises. Meanwhile Necessary assumption questions have "new concepts" but here it's known as the "missing piece" and it's found in the premises not in the conclusion
Amazing lesson. I have struggled a lot with NA questions on recent prep tests, but I felt the Core Curriculum was not really what I needed to re-review. This high level summary was perfect. After reviewing this video and taking notes on the main lessons, I think I was able to identify the key areas I was struggling with. Thank you very much!
I ended up picking D because I knew A was reversed. But the word "sometimes" in D threw me off. If making major changes in their behavior is the necessary condition, doesn't the word sometimes make the answer wrong?
@praksesprepper The premise tells us that reptiles are "incapable" of making major changes in behavior. So the link the author assumes is:
incapable of major changes --> incapable of complex reasoning
contrapositive:
capable of complex reasoning --> capable of major changes
D says sometimes because it's matching up to "capable of major changes". In fact D would be wrong if it said "if reptiles were capable, they would always make major changes" because that's too extreme for the actual line of reasoning.
@Kevin_Lin That makes sense- thank you so much!!
im scared
Ahhh yes my biggest weakness
i always confuse sufficient and necessary. i can always narrow it down to 2 possible answers, yet i tend to choose the one that confuses necessary and sufficient. i dont know how to correct this ugh.
@Ssss Return to the Conditional and Set Logic module -- this is probably the source of a lot of your confusion with sufficient and necessary conditions. It can take a lot of practice to get fluent in these concepts.
@Ssss One thing that helped me when I was first starting with conditional logic is to map out every single question and answer that uses conditionals.
I would take a practice question under normal time control (ie try to answer efficiently), then on blind review, I would diagram the question, understand from that diagram what piece was missing that I should be looking for, then diagram all the answers, and understand why the wrong answers didn't fit/interact with the diagram of the question.
This will help you actively expose yourself to sufficiency/necessity, and you will soon be able to "diagram" mentally and see the missing pieces without having to put pen to paper.
for some reason I do better on necessary assumption question than sufficient assumption questions... I'm just so confused on why necessary assumption makes more sense to me than sufficient. I think I view them as the same? is there a specific difference between them that others have noticed?
I feel that this is my weak suit lol
Such a helpful explainer with great take-away tips; thank you Kevin!
One question: in Question 4 re: macaque monkeys, you mentioned that B is easy to negate because you can just take away the "not" in a sentence that is "Subject is not Predicate", ie negated AC becomes "Subject is Predicate".
Is it it always okay to do that, or are there some parameters around when we can do that? (for example, if the Subject is singular not plural)?
Or are there cases where just dropping the "not" may not work how we need it to for a negation test? Ie, where taking a way the "not" needs to be a "some" instead of "all" relationship? ie, "Subject is not Predicate" needs to be negated to "Subject is SOMETIMES Predicate" or "Some Subject(s) are Predicate" to properly evaluate whether it breaks the argument?
Is it wrong to assume in Q2 AC A is too broad as well because it says "Animals" As opposed to the reptile in question? It feels like a subtlety that the argument is not as broad as AC A makes it out to be?
@Danny_F I think this is debatable. The "reptile" aspect of the argument didn't seem to be play a role in the logic, so arguably the author's assumption isn't narrowed to reptiles alone.
WOW 7 hit me luck a truck, Thank you Kevin, you have been so helpful.
HOLYYYY question 6 was not it man.
this is super helpful.
which lesson would you advise is best for becoming a pro at negation?
@e.wimoine The second half of the Logic of Intersecting Sets module discusses this! But you bring up a good point; maybe there should be a Fast Track - Negation
@Kevin_Lin yes, a Fast Track - Negation video would be super helpful! Especially where negation leads to double negatives; how we can read them in a way that makes more sense.
@Kevin_Lin Yes please!