"The only" as a sufficient conditional indicator

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• 6 Likes

  CFC152436 Alum Member

  June 2014 284 karma

  1. The only students with brown hair are students with brown eyes
  BH ---> BE
  
  2. Students with brown hair always have brown eyes.
  BH ---> BE
  
  Have you done the worksheets at the end of the lesson group? They should have plenty of examples of these (and other) logical indicators.
• 11 Likes

  anne2hoang Free Trial Member

  June 2014 edited June 2014 226 karma

  "If someone got an A on the test, then they must have studied."
  Sufficient condition: “to get an A.”
  Necessary condition: “must have studied.”
  A -> S
  
  Different variations of A -> S:
  
  1. “The only” people who got an A, must have studied.
  “The only” is a sufficient condition indicator.
  
  2. “Only” someone who studied can get an A on the test.
  “Only” is a necessary condition indicator.
  
  3. You will get an A “only if” you study.
  “Only if” is necessary condition indicator.
  
  
• 12 Likes

  anne2hoang Free Trial Member

  June 2014 edited June 2014 226 karma

  Does anyone know if there is a lesson on 7sage on how to distinguish the different only's? I don't mean a drill worksheet, but an actual video lesson. Thanks!
  
  Note to Powerscore users:
  Powerscore did not include "the only" on their list of sufficient condition indicators. But they did include "only" and "only if" as necessary condition indicators. So if you are relying on Powerscore, avoid the mistake of treating all the "only's" as necessary condition indicators. Since it is possible to have a sufficient condition indicator containing the word "only." And that would be "the only."
  
  Note to MLSAT users:
  They don’t distinguish between the only’s either. It is funny because they love to distinguish all sorts of things. But there is no mention of the different only’s. They have a section on “if” verses “only if,” another section on “except perhaps and unless.” Heck, one of their lessons start even starting out by saying how important the word “only” is. “The word only could be the single most important word on the LSAT. It shows up all over the place” (p. 365). Seriously?
• kraft.phillip Free Trial Member Inactive Sage

  June 2014 444 karma

  Thanks for posting this. I've had some trouble with this differentiation as well. I don't think MLSAT's LR text deals with it at all. It's certainly an awkward sentence construction.
• 1 Like

  kraft.phillip Free Trial Member Inactive Sage

  June 2014 444 karma

  Examine these constructions:
  
  Kids with brown hair are the only kids with brown eyes.
  VS
  The only kids with brown hair are the kids with brown eyes.
  
  Which is which condition?
• 1 Like

  anne2hoang Free Trial Member

  June 2014 226 karma

  If someone has brown hair, then they have brown eyes.
  BH -> BE
  
  I am going to rephrase your question:
  
  Only the kids with brown eyes have brown hair.
  VS
  The only kids with brown hair are the kids with brown eyes.
  
  Now you tell me which only is which!
  
• 1 Like

  kraft.phillip Free Trial Member Inactive Sage

  June 2014 444 karma

  anne,
  
  The first uses "only" as a necessary condition indicator:
  BH->BE
  
  The second uses "the only" as a sufficient condition indicator:
  BH->BE
  
  They are both the same, then, logically. No?
  
  My question, more specifically, is whether the phrase "the only" changes to a necessary condition indicator when it is located in the middle of the sentence.
  
  The kids with brown hair are the only kids with brown eyes.
  Is it still:
  The only=suff, so
  BE->BH.
  If Brown eyes, then Brown hair.
  
  
• 11 Likes

  J.Y. Ping Administrator Instructor

  June 2014 edited June 2014 14225 karma

  Hey guys, this is a great discussion and I want to offer some clarity.
  
  The short answer is: just follow the rule. "The only" introduces sufficient conditions.
  
  There are only two usages of "the only" to form grammatical sentences.
  
  The first grammatically correct usage:
  The only X's (insert modifiers) are the Y's (insert modifiers).
  
  In this form, the Y's must call back, point back, refer back to the X's.
  
  The translation is X-->Y
  
  For example:
  The only kids with messy hair are the kids with brown eyes.
  
  The only kids (X) with messy hair (modifier) are the kids (Y) with brown eyes (modifier).
  
  Notice that Y refers back to X. You could have just as easily said:
  The only kids with messy hair are the ones with brown eyes.
  
  Translated: If you're a kid with messy hair, then you have brown eyes. If you don't have brown eyes, you don't have messy hair.
  
  Another example:
  The only students who got an A, are the ones who studied. (The original sentence as written - see way above - was not grammatical, so I amended it.)
  
  The only students (X) who got an A (modifier), are the ones (Y) who studied (modifier).
  
  Translated: If you got an A, then you studied. If you didn't study, then you didn't get an A.
  
  One more example:
  The only philosophical works that continue to be studied with diligence and high scrutiny by generations upon generations of scholars and sages are those that offer deep insight into the nihilistic nature of man's existence.
  
  The only philosophical works (X) that continue to be studied with diligence and high scrutiny by generations upon generations of scholars and sages (modifier) are those (Y) that offer deep insight into the nihilistic nature of man's existence (modifier).
  
  Translated: If you're a philosophical work that blah blah blah, then you offer deep insight blah blah blah. If you don't offer deep insight, then you're not a philosophical work.
  
  The second grammatically correct usage:
  Y's (insert modifier) are the only X's (insert modifier).
  
  In this form, the X's must call back, point back, refer back to the Y's.
  
  The translation is X-->Y
  
  For example:
  Kids with brown eyes are the only kids with messy hair.
  
  Kids (Y) with brown eyes (modifier) are the only kids (X) with messy hair (modifier).
  
  Notice that X refers back to Y. You could have just as easily said:
  Kids with brown eyes are the only ones with messy hair.
  
  Translated: If you have messy hair, then you have brown eyes. If you don't have brown eyes, then you don't have messy hair.
  
  Another example:
  Horses are the only animals that are strong.
  
  Horses (Y) are the only animals (X) that are strong (modifier).
  
  Notice "animals" (X) points back to "horses" (Y). You can't say "Horses are the only dogs that are strong" because wtf.
  
  Translated: If you're a strong animal, then you are a horse. If you are not a horse, then you are not a strong animal.
  
  One more example:
  Maniacal and over the top performances are the only effective ones.
  
  Maniacal and over the top (modifier) performances (Y) are the only effective (modifier) ones (X).
  
  Notice the modifiers appear first.
  
  Translated: If it's an effective performance, then it was maniacal and over the top. If it was not maniacal or not over the top, then it was not effective.
  
  
• anne2hoang Free Trial Member

  June 2014 226 karma

  
  Hi J.Y. Ping,
  
  It is nice to finally meet you.
  
  The only thing I would like to add to your post is that indicators do not switch teams. A sufficient condition indicator will always introduce a sufficient condition. It does not matter where the indicator is placed within the sentence.
  
  This same rule applies to conclusion indicators. “Therefore” will always be a conclusion indicator. It does not matter if “therefore” is placed at the beginning or middle of the sentence.
  
• 1 Like

  J.Y. Ping Administrator Instructor

  June 2014 14225 karma

  Hi Anne, it's nice to meet you too!
  
  I take it you're not enrolled in our course? You should definitely check it out. I promise you it's better than the curriculum you're currently using.
  http://7sage.com/lsat-course-reviews/
  
  (The reason I say this is because I gathered from your comment that you weren't exposed to the prior lessons in our course that contextualize this discussion.)
  
  
  
• anne2hoang Free Trial Member

  June 2014 226 karma

  I just got called out for not being enrolled. Just kidding! You are correct in that I do not have access to the lessons. I am still trying to decide between a few LSAT courses. There are pros and cons to every single one of them.
• annkang1005 Alum Member

  June 2014 63 karma

  Wow thanks so much for the posts guys! Had difficulty gaining access to wifi in my area for hours after the post and look at this This was very VERY helpful.
• 1 Like

  annkang1005 Alum Member

  June 2014 63 karma

  + I just want to say a huge thanks to JY for providing many examples and especially breaking down "the only" into two grammatical usages!
• Mister-eeee Alum Member

  August 2015 20 karma

  @anne2hoang said:
  Powerscore did not include "the only" on their list of sufficient condition indicators. But they did include "only" and "only if" as necessary condition indicators.
  

  @anne2hoang,
  
  I didn't notice Powerscore failed to distinguish the difference between the various "only's"!
  
  I appreciate you pointing that out
• 2 Likes

  Pacifico Alum Inactive ⭐

  August 2015 8021 karma

  Whoa blast from the past... How did you even find this thread?
• tanes256 Alum Member

  August 2015 2573 karma

  ^^^^^ I said the same thing! LOL
• notwilliamwallace Alum Member

  April 2016 1049 karma

  Sorry for reviving an old thread, but I had a quick question about this topic...In the LSAT Trainer, one the drill statements is "In order to build a desk, the only materials needed are wood, a saw, nails, and a hammer. I have all of those things, so I should be able to build a desk".
  
  From what I learnt, "the only" introduces a sufficient condition. So this becomes: WSNH --> BD (If I have woods, saw, nails, and a hammer, I will be able to to build a desk). Meaning, if we satisfy the WSNH condition, we will guarantee that we will be able to build a desk. However, per the Trainer, this is a flawed statement because it fails to consider that there might be other requirements to build a desk (like knowing how to use a hammer). Going from that logic, shouldn't the lawgic statement for this be: BD --> WSNH. Here, it is necessary that you have WSNH but on their own, they don't guarantee that you will be able to build a desk. Am I missing something? Is my lawgic totally wrong? Is today a good day to eat pizza (okay, you can ignore this last one)?
• dcdcdcdcdc Alum Member

  April 2016 382 karma

  I believe that your example would be interpreted as "if it is a material needed to build a desk, then it is wood, a saw, nails and a hammer."
  
  This doesn't lead to the outcome of having built a desk.
  
  I often rely on an example that you might hear often: " the only way to...is..." and another way to reinforce the understanding that I use is to attempt to repeat the first element (in an abstract sense) in regards to the second element. That is the use of "materials" for this example.
• 2 Likes

  quinnxzhang Member

  April 2016 edited April 2016 611 karma

  @notwilliamwallace, In the first sentence, "the only" is modifying "materials needed", not "in order to build a desk". The expression "in order to build a desk" is an additional modifier for "materials needed". Bracket this latter modifier for a moment. The first sentence reads "the only materials needed are WNSH". The rule above correctly gives you "materials needed → WNSH". Once you see that "in order to build a desk" is modifying "materials", you see that that expression is just a longer part of the antecedent, namely "materials needed to build a desk → WNSH".

  @notwilliamwallace said:
  Going from that logic, shouldn't the lawgic statement for this be: BD --> WSNH.
  

  This is a correct inference to draw, but not because of "the only", nor because this is what the first sentence is saying. Rather, this is a correct inference because the "needed" in the first sentence indicates necessity, from which you can infer that WNSH are necessary for building a desk. That is, "the only materials needed to build a desk are WNSH" implies "WNSH are needed to build a desk", the latter of which can be represented by your "BD → WNSH" diagram.
• notwilliamwallace Alum Member

  April 2016 1049 karma

  Good point. Also, I was eyeballing the statement again and it clearly says, "...the only materials a person needs are wood, a saw, nails, and a hammer..." So, if you ask what's needed, it tells you that wood, a saw, nails, a hammer are needed, making these the necessary condition. I guess this question proves the point to not be so mechanistic but also to use intuition to figure out the lawgic behind statements. Thanks for your help @dcdcdcdcdc
• notwilliamwallace Alum Member

  April 2016 1049 karma

  Awesome explanation as always @quinnxzhang ... your help is always much appreciated. As you mentioned to me before, it is to my demise to be always using mechanistic ways when approaching lawgic. Thanks again
• 1 Like

  hlsat180 Free Trial Member

  April 2016 edited April 2016 362 karma

  @notwilliamwallace to tag on the detailed explanation by @quinnxzhang (his comments provide invaluable mini-lessons in logic!) the word "only" ALWAYS modifies the necessary condition, but "the only" works as sufficient condition indicator because of its typical placement in a sentence.
  
  For example: The only way to become rich is to work hard.
  
  Diagrammed: Become Rich --> Work Hard
  
  The common interpretation is mechanistic (i.e., "The only" is a sufficient condition indicator for "become rich"). But the (actual) technical explanation is "The only" modifies "way" - and "way" refers to "work hard" (the consequent/necessary condition). The confusion is due to the physical separation of these terms in this type of sentence.
  
  For example: To become rich the only way is to work hard.
  
  This sentence says the same thing, yet mechanistically applying the sufficient indicator rule could lead you to diagram incorrectly. Similarly, this explains your example from The LSAT Trainer.
  
  I still apply mechanistic rules (saves time!) but found this deeper understanding of "the only" reinforced my confidence and retention. Plus, now there is "only" one universe.
• notwilliamwallace Alum Member

  April 2016 1049 karma

  Makes sense. Thanks for that explanation @hlsat180
• Efficiency Bill Member

  April 2020 97 karma

  @"kraft.phillip" said:
  anne,

  The first uses "only" as a necessary condition indicator:
  BH->BE

  The second uses "the only" as a sufficient condition indicator:
  BH->BE

  They are both the same, then, logically. No?

  My question, more specifically, is whether the phrase "the only" changes to a necessary condition indicator when it is located in the middle of the sentence.

  The kids with brown hair are the only kids with brown eyes.
  Is it still:
  The only=suff, so
  BE->BH.
  If Brown eyes, then Brown hair.

  I'd really like to emphasize this distinction between "the only" and "only the" - The former is a sufficient condition indicator, as taught, but the existence of the latter ("only the") confused me. Thanks for this 6 year old post for clarifying this!