Does anyone have another word that can be used to describe the meaning of sufficient in the context of conditional reasoning? That part is really not sticking to me. Any tips would be greatly appreciated.
so just to be clear does something have to be sufficient for it to be necessary. because I understand that even is something is necessary that doesn't make it enough (sufficient) to be true. its always A - B it cant be B- A.
@Dean_Dyrmishi Yup, I like to think of the example "you can't have dessert until you finish dinner". To diagram that, you negate whatever comes after the "until" and make that the sufficient condition.
AKA if you don't finish dinner, you can't have dessert: Finish dinner --> Dessert
Or if you want dessert, you must finish dinner: Dessert --> Finish dinner
Sadly, I still don't understand how to distinguish sufficient from necessary conditions. In the abstract, I understand them when I use symbolic logic, but in practice they don't make sense.
I'm confused about "if not" indicators ("unless" and without"): group 3 and "then not" indicators ("no" and "none") : group 4, are these necessary conditions?
@EricPreneta well okay Q1 makes sense. I think the explanations are great but can add complexity to what intuition was providing. But still accept the required mechanical approach to be successful in the complex LSAT questions to come...
i had to watch this video twice to really understand sc and nc. during my second try i made sure to take notes, draw circles, and speak outloud - highly recommend!
According to the loophole. To create contraposatives: read backwards and negate as you go. So A to B is NOT B to NOT A. Regardless of how long the chain is.
It might be worthwhile to point out that taking the contrapositives of both A and B then testing those in place will provide a clear understanding of why the sufficient and necessary conditions are swapped in A.
The nasty trick here is that a billion dollar donation would be reasonable considered generous by any measure, so its a REAL LIFE generous act. However, the damn LSAT often messes with me by filling my mind with real life nonsense to mask understanding the real argument from me, which in this case is..
Not SelfInterest then Generous, which cannot be concluded from either of the valid forms of the first argument.
So perhaps the REAL TRICK (psychological) here, and elsewhere, is to cross out all real world meaning. So just ignore or cross out the sentence "This business owner donated a billion to a charity" and focus only on Not SelfInterest Thus Charity
@nr No. Your translation from words to symbols is not correct.
Try this....
Not X unless Y is equivalent to X only if Y.
The rule for that conversion is to negate the antecedent and substitute Only If for Unless.
Not Daytime Unless BirdsSing translates to
Not (Not Daytime) Only If BirdSing
Daytime Only If BirdSing
And you can substitute Then for Only If, so If X Then Y
If Daytime then Birdsing
SkyBlue Only If Datime is If SkyBlue then Daytime
You can see how they combine
If SkyBlue Then DayTime Then BirdsSing
If SkyBlue Then BirdSiing
For me, the key step is to never reason with Unless, but to always do the Unless/OnlyIf translation first. Then OnlyIf/Then synonym swap to put everything in standard language, which is easier to "think" about; keep in my head without a meltdown.
I know it'll take practice and time, but does anyone have a quick trick to find the contrapositive? I think I'm overthinking it. Very good video though!!
on Q2 with the ice on the sidewalk, why is it not invalid for being inverse of the relationship established? The diagramming led us to If there is ice -> sidewalk is not open to the public. This is a different necessary condition than If sidewalk open to the public -> it doesn't have ice. What am i missing here?
@DiyaOmkar219 probably, it's a lot. i wasn't planning on taking notes and then started the video and found taking notes is the only way i really grasped it.
@Kevin_Lin With the pay raise example, you say "In order to get a raise one of the things you must do is hit your target sales numbers, [...]." I was definitely tired/overthinking it but hearing "one of the things" in relation to the necessary condition made me think it was just sufficient.
@Aletariel "In order to bake a cake, one of things you must have is flour." "Must" is what tells us it's a necessary condition. I just said "one of the things" to emphasize that we don't know it's the only thing you need.
People might mistakenly think that "You'll get a raise only if you meet your sales target" means that meeting your sales target is the one and only thing you need to do to get a raise. But that's not what it means. It means meeting your sales target is necessary. We don't know whether there are other things that are also necessary.
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72 comments
Does anyone have another word that can be used to describe the meaning of sufficient in the context of conditional reasoning? That part is really not sticking to me. Any tips would be greatly appreciated.
I love the circle diagram! It really helped me understand the actual meaning of sufficient and necessary.
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so just to be clear does something have to be sufficient for it to be necessary. because I understand that even is something is necessary that doesn't make it enough (sufficient) to be true. its always A - B it cant be B- A.
@BlessingOyedele890 correct, that is how I understood it
great video! deep into lsat prep and needed a refresher. Was hesitant to scroll through all the modules and search for this.
Quick and niche question: Would we treat "until" the same way we would treat "unless"
@Dean_Dyrmishi Yup, I like to think of the example "you can't have dessert until you finish dinner". To diagram that, you negate whatever comes after the "until" and make that the sufficient condition.
AKA if you don't finish dinner, you can't have dessert:
Finish dinner-->DessertOr if you want dessert, you must finish dinner: Dessert --> Finish dinner
It's the same thing with "unless"
ooooh the way I got all the quiz questions wrong...
I’m dead @ the Kim k shade
Sadly, I still don't understand how to distinguish sufficient from necessary conditions. In the abstract, I understand them when I use symbolic logic, but in practice they don't make sense.
@dxyonna just try to memorize the the sufficient and necessary indicators. They're very helpful.
I'm confused about "if not" indicators ("unless" and without"): group 3 and "then not" indicators ("no" and "none") : group 4, are these necessary conditions?
@CayleeJoanMcDougall right there with you. can only replay so many times LOL. going to try once more and then come back at later time!
@EricPreneta well okay Q1 makes sense. I think the explanations are great but can add complexity to what intuition was providing. But still accept the required mechanical approach to be successful in the complex LSAT questions to come...
i had to watch this video twice to really understand sc and nc. during my second try i made sure to take notes, draw circles, and speak outloud - highly recommend!
did anyone else notice the lawer typo lol
in part 2 i don't understand group 3 with the indicator words "unless" and "without"
the video is not showing for me?
@Kmwalt025 How about this:
@Kevin_Lin Thanks, that worked. the video is now showing on the page as well. My computer may have been glitching?
According to the loophole. To create contraposatives: read backwards and negate as you go. So A to B is NOT B to NOT A. Regardless of how long the chain is.
It might be worthwhile to point out that taking the contrapositives of both A and B then testing those in place will provide a clear understanding of why the sufficient and necessary conditions are swapped in A.
Missing step?
Wait, wait wait...
Premise given:
If SelfInterst Then Not Generous
SI -> ~G
G -> -SI If Generous the Not SelfInterst
The nasty trick here is that a billion dollar donation would be reasonable considered generous by any measure, so its a REAL LIFE generous act. However, the damn LSAT often messes with me by filling my mind with real life nonsense to mask understanding the real argument from me, which in this case is..
Not SelfInterest then Generous, which cannot be concluded from either of the valid forms of the first argument.
So perhaps the REAL TRICK (psychological) here, and elsewhere, is to cross out all real world meaning. So just ignore or cross out the sentence "This business owner donated a billion to a charity" and focus only on Not SelfInterest Thus Charity
~SI -> G One of the invalid foms.
Teemo chuckle jumpscare 😭
I got confused on the following chaining conditional example.
The sky looks blue only if it's daytime. Unless you hear birds singing, it's not daytime. If the sky looks blue, then you'll hear the birds singing.
Below is how is I mapped it out - is this the correct mapping?
-Blue sky -> daytime
-daytime -> birds singing
-blue sky -> birds singing -> daytime
@nr No. Your translation from words to symbols is not correct.
Try this....
Not X unless Y is equivalent to X only if Y.
The rule for that conversion is to negate the antecedent and substitute Only If for Unless.
Not Daytime Unless BirdsSing translates to
Not (Not Daytime) Only If BirdSing
Daytime Only If BirdSing
And you can substitute Then for Only If, so If X Then Y
If Daytime then Birdsing
SkyBlue Only If Datime is If SkyBlue then Daytime
You can see how they combine
If SkyBlue Then DayTime Then BirdsSing
If SkyBlue Then BirdSiing
For me, the key step is to never reason with Unless, but to always do the Unless/OnlyIf translation first. Then OnlyIf/Then synonym swap to put everything in standard language, which is easier to "think" about; keep in my head without a meltdown.
I know it'll take practice and time, but does anyone have a quick trick to find the contrapositive? I think I'm overthinking it. Very good video though!!
@Bmariachi01 Flip the sufficient and necessary and Negate both!
For example: All people who eat leftover egg salad will get food poisoning.
Eat leftover egg salad---> will get food poisoning
flip and negate ( reverse and do the opposite, if positive then negative or if negative then positive)
Contrapositive: Will not get food poisoning---> No (doesn’t) eat leftover egg salad.
on Q2 with the ice on the sidewalk, why is it not invalid for being inverse of the relationship established? The diagramming led us to If there is ice -> sidewalk is not open to the public. This is a different necessary condition than If sidewalk open to the public -> it doesn't have ice. What am i missing here?
@ElizabethSacco If ice --> side not open
Doesn't that prove if the sidewalk IS open, then there is NO ice? (This is the contrapositive)
A --> B
means the same thing as
Not B --> Not A
The most understanding I've had in any lesson! Thanks Kev
Does "only if" always signal the necessary?
@LaneyWilliams Yes, it does.
@Kevin_Lin Awesome, thank you!
should we be taking notes on this??
@DiyaOmkar219 probably, it's a lot. i wasn't planning on taking notes and then started the video and found taking notes is the only way i really grasped it.
I was doing really good understanding it but then halfway through he said something and it just "uncliked" everything for me.
@timwes21 Same it was his examples in "Only If" for some reason
@Aletariel What about the "only if" examples don't make sense to you? If it that you keep wanting to read "X only if Y" as "If Y, then X"?
@Kevin_Lin With the pay raise example, you say "In order to get a raise one of the things you must do is hit your target sales numbers, [...]." I was definitely tired/overthinking it but hearing "one of the things" in relation to the necessary condition made me think it was just sufficient.
@Aletariel "In order to bake a cake, one of things you must have is flour." "Must" is what tells us it's a necessary condition. I just said "one of the things" to emphasize that we don't know it's the only thing you need.
People might mistakenly think that "You'll get a raise only if you meet your sales target" means that meeting your sales target is the one and only thing you need to do to get a raise. But that's not what it means. It means meeting your sales target is necessary. We don't know whether there are other things that are also necessary.