Doubt in necessary assumption

Comments

• runiggyrun Alum Inactive Sage Inactive ⭐

  January 2016 2481 karma

  The example you are giving is a Sufficient Assumption. With the two premises, (one cup of coffee is not too much caffeine AND she only drinks one cup of coffee) and knowing "she doesn't drink anything else containing caffeine" you are guaranteed the conclusion. She does not consume too much caffeine.
  It's not a Necessary assumption because, while the negation does somewhat hurt the argument (so it would make for a valid answer for a weakening question) it doesn't destroy it. She could drink one cup of coffee AND a coke and still be under the "too much caffeine" limit.
  A necessary assumption always destroys the argument when negated, rather than just weakening it.
• Grey Warden Alum Member

  February 2016 edited February 2016 813 karma

  Thanks a lot @runiggyrun
• Alejandro Member Inactive ⭐

  February 2016 edited February 2016 2424 karma

  I would say "If she consumes any caffeine other than a cup of coffee on a given day, then that amount doesn't make her consume too much caffeine in a day" would be considered a necessary assumption.
• runiggyrun Alum Inactive Sage Inactive ⭐

  February 2016 2481 karma

  @Alejandro that sounds about right.
  @"Grey Warden" - the fact that a certain answer can be right or wrong depending on what the question stem is asking for, especially when applied to SA/NA/weaken and learning to discern the difference between the three requirements was one of the most useful "aha!" moments I've had studying for LR. For these question types I always write down NA or SA or W right next to the stem, just to remind myself what exactly it is that I'm looking for in the answer choices.
• Alejandro Member Inactive ⭐

  February 2016 2424 karma

  @runiggyrun agreed. And @"Grey Warden" just breath and take some time to internalize the concept. Don't sweat it. I think if a question like this appeared on the LSAT it would be one of the curve-breaker questions.
• MrSamIam Inactive ⭐

  February 2016 edited February 2016 2086 karma

  Negation: "Coffee is NOT the only substance she drinks, which contains caffeine."
  It could hurt the argument. Or, possibly not. So what if she consumes something else which contains caffeine? Without any other premises, we can fairly assume that daily, she uses a liquid dropper to drip 1/10 of a milliliter of tea on her tongue. Does that fulfill the negation? Yes, she has now consumed TWO caffeinated liquids. Does it hurt the argument? Probably not, unless you consider an additional 5-10 mg of caffeine a lot, even in spite of the fact that her coffee probably contains around 110+ mg - we're just making assumptions now, so I'll stop.
  
  If the above is a tad confusing, try this one:
  With the negation, she would have to consume at least one other caffeinated drink. Okay, so lets meet the minimum requirement. She now consumes two caffeinated drinks. To make this easier, lets throw in some arbitrary numbers.
  Her coffee: About 130 mg of caffeine per cup.
  Her second caffeinated drink (some rare tea that is incredibly low in caffeine, but does in fact contain caffeine): 5 mg per cup.
  Now ask yourself, does adding 5 additional mg of caffeine to the currently consumed 130 mg really weaken the argument that she isn't consuming too much caffeine? I don't think so. If 130 mg isn't "too much" then surely an additional 5 wouldn't make it "too much."
• 1 Like

  DumbHollywoodActor Alum Inactive ⭐

  February 2016 7468 karma

  Good work, @MrSamlam.
  
  @"Grey Warden" Here’s the relevant lesson for negation in the curriculum: https://7sage.com/lesson/how-to-negate-statements-in-english/

  @"Grey Warden" said:
  Coffee is the only substance she consumes that contains caffeine
  

  Before we negate this statement, it might help to translate it into a more logically understandable form. I like If-then.
  
  If she consumes a substance that contains caffeine, then it’s coffee.
  
  Why? Because “the only” is a group 1 indicator.
  
  To negate this statement, we make it an intersecting statement (or a SOME statement) with the necessary condition negated.
  
  She sometimes consumes substances that contain caffeine and they’re not coffee.
  
  If that were true, then she might consume too much caffeine, hence ruining the argument.
• Alejandro Member Inactive ⭐

  February 2016 2424 karma

  @DumbHollywoodActor if she consumes substances that contain caffeine that are not coffee doesn't necessarily ruin the argument. Think about it!
• 1 Like

  DumbHollywoodActor Alum Inactive ⭐

  February 2016 7468 karma

  Doh!

  @Alejandro said:
  Think about it!
  

  I was so focused on the task at hand, negating statements, that I really wasn’t paying to the conclusion. Yeah, the negation would only weaken the argument, not kill it outright. +1 to you @Alejandro
• 1 Like

  J.Y. Ping Administrator Instructor

  February 2016 14214 karma

  All of you guys are so on point!
• Grey Warden Alum Member

  February 2016 edited February 2016 813 karma

  Thank you so much guys, you are all so awesome!! This helped a lot in clarifying the nuances existing between SA, NA and weaken answer choices in NA questions.
  When we say that negation of the answer choice does not destroy the 'argument', it seems to me that the focus is more on the destruction of the 'conclusion' of the argument from the negation of the answer choice.
  In the example here, the conclusion was based on her drinking only one cup of coffee a day. When we apply the negation as @DumbHollywoodActor rightly pointed out it translates to 'She sometimes consumes substances that contain caffeine and they’re not coffee'
  In such a case the conclusion may still follow as you guys have rightly said, however, the support relationship between the premise and the conclusion is weakened as in the premise 'not consuming more than a cup of coffee' is not so much indicative of the conclusion that 'she does not consume too much caffeine.'
  I am now trying to understand the subtleties in how the negation of the necessary assumption destroys the relationship between the premise and conclusion and how it sometimes merely weakens without destroying in order to avoid falling for trap answer choices, hoping I will get there.
• runiggyrun Alum Inactive Sage Inactive ⭐

  February 2016 2481 karma

  @"Grey Warden" you've figured it out perfectly. Telling the difference "on the fly" will become second nature with a bit of practice, now that you know what to look for. Maybe you'll even find yourself smirking at the test makers thinking "aha, I see what you did there sneaking in an NA answer for a SA question. Nice trap. Not falling in it"