Necessary Assumption

  • Necessary Assumption Questions, Negation Test, and Must be True Qs from “LSAT Blog: Ace the LSAT”
    • Discusses a “common and effective strategy” for attacking these questions
    • The “Negation”/”Denial” Test
    • “As the name implies, this “test” requires you to negate each of the answer choices. The correct answer choice, when negated, renders the argument invalid. The argument cannot be valid if the necessary assumption is not true. After all, the necessary assumption is, in fact, necessary for the argument to work” [emphasis mine]
    • “Ask yourself as you read each answer choice, does this *need* to be true for the evidence to require the conclusion?” [emphasis mine]
    • Negate the answer to the logical opposite, not polar opposite (“All people are standing” –> “Not all people are standing”)
    • Necessary Assumption questions are in the Must be True category
    • Correct answer does not bring in any new information
  • What is a Necessary Assumption? from Manhattan Prep Forums
    • “A necessary assumption is something that is REQUIRED for the argument to be true, meaning if this assumption is false, then the argument CANNOT be valid. The conclusion WILL not follow given the evidence.”
    • “Necessary assumptions, when negated, will destroy the argument (meaning, you can’t definitively draw the conclusion given the premises).” [emphasis mine]
    • “You negate the answer choice, and then add it into the argument. If it’s truly a necessary assumption, you should find yourself saying “Well, how can we draw that conclusion then?!”” [emphasis mine]
    • “If it’s not a necessary assumption, the negated form should be irrelevant to whether we can draw the conclusion or not.” [emphasis mine]
  • How to Master LSAT Logical Reasoning Necessary Assumption Questions by Lawschooli.
    • “When you hear the word ‘assumption’, I want you to just think ‘premise’. In an LSAT LR question, a necessary assumption is just another premise that supports the conclusion, only it goes unsaid. Commit this to memory: a necessary assumption is really just an unstated premise.”
    • Look for leaps and assumptions
    • Watch for leaps between cause and effect. Does the stated cause necessarily or only cause the effect?
    • “Spotting assumptions can be tough. The truth is that your brain is probably so good at understanding unstated assumptions that you don’t often even notice them.”
    • “…you are trying to identify the passage author’s assumptions, not make your own. Remember that.” [emphasis mine]
    • “You simply see what would happen to the argument if the assumption you are testing is not true. If the argument gets blown all to bits by negating an answer choice, then bam, you know that assumption was necessary. It’s the right answer.” [emphasis mine]
    • Excellent demonstration of negation!
    • “If you can imagine any reason why the argument can survive without a premise, it’s not that right answer.”
  • How to Approach Necessary Assumption Questions by 7sage
    • “Necessary assumptions can wreck an argument.” [emphasis mine]
    • “Argument (valid) –> Necessary Assumption (true)
      /Necessary Assumption –> /Argument” [emphasis mine]
    • There are two types of Necessary Assumptions: Shield & Bridge
      • “Answers to shield type necessary assumption questions protect your argument from being wrecked.” [emphasis mine]
      • Bridge: “these answer choices point out gaps in the logic of the argument.” [emphasis mine]; “Bridge questions trade on your inclination to conflate two different ideas“; you must make the connection, and that connection must be vital to the conclusion; “It’s your job to find this bridge in the answer choice that takes you from the premise to the conclusion.
  • What Necessary Assumption Means by Foxlsat.com
    • “Your task is to identify an answer that must be true, in order for the argument to even conceivably be true. In other words, it’s asking you to identify an answer that, if untrue, would cause the argument to fail. In other words, it’s asking for a necessary condition.” [bolding mine, italics and link theirs]
  • Necessary Assumption Questions Suck Ass by thedreadedlsat.tumblr.com
    • “I think of Necessary Assumption questions as Weaken questions. I look for ways to weaken the argument and then search the negated answer choices that weakens the argument.” [emphasis mine]
    • Pay attention to the scope of the stimulus and the answer choices, gives a good explanation of negation
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