{"id":12156,"date":"2019-09-06T00:38:48","date_gmt":"2019-09-06T05:38:48","guid":{"rendered":"http:\/\/www.kaptest.com\/blog\/prep\/?p=12156"},"modified":"2020-09-11T20:40:51","modified_gmt":"2020-09-11T20:40:51","slug":"lsat-logical-reasoning-inference-vs-assumption","status":"publish","type":"post","link":"https:\/\/wpapp.kaptest.com\/study\/lsat\/lsat-logical-reasoning-inference-vs-assumption\/","title":{"rendered":"LSAT Logical Reasoning: Inference vs. Assumption"},"content":{"rendered":"

You\u2019re having lunch with your friend Bob, and you suggest splitting an order of onion rings. Bob says that he doesn\u2019t eat onion rings. In real life, you could draw several valid inferences from this: maybe Bob doesn\u2019t like onions, maybe he\u2019s watching his weight so he\u2019s avoiding fried foods, maybe he doesn\u2019t like crunchy appetizers. In real life,<\/i> those would all be acceptable inferences, because the real-world definition of infer is to do any of the following:
\n1. to derive by reasoning; conclude or judge from premises or evidence: e.g., They inferred his anger from his heated denial.<\/i>
\n2. (of facts, circumstances, statements, etc.) to indicate or involve as a conclusion; lead to.
\n3. to guess; speculate; surmise.
\n4. to hint; imply; suggest.
\n\u201cInfer\u201d is, as you can see, a word with fairly flexible meaning. We most often use it in day-to-day life to mean \u201cmake an educated guess.\u201d If your friend Bob says he doesn\u2019t eat onion rings, you apply your existing knowledge about the possible reasons someone could have for not enjoying a tasty breaded and deep-fried ring of onion, and you make an educated guess as to what his reasons could be. On the LSAT, however, \u201cinference\u201d has a different meaning. Think of inferring as the process of deriving the strict logical consequences of assumed premises.
\nOn the LSAT, therefore, if you are told that Bob doesn\u2019t eat onion rings, you can derive two logical consequences from that premise:<\/p>\n

    \n
  1. If Bob is eating, has eaten, or will eat something, it isn\u2019t an onion ring, and<\/li>\n
  2. If someone is eating, has eaten, or will eat an onion ring, that person is not Bob.<\/li>\n<\/ol>\n

    The correct answer to an inference question<\/a> on the LSAT will follow directly from the evidence provided; it is NOT merely an educated guess, but is instead the logical consequence of the assumed premises.
    \nNotice that just based on five words\u2014\u201cBob doesn\u2019t eat onion rings\u201d\u2014we can draw two possible inferences. Now think of how many words you might see in the average LSAT question, and you\u2019ll understand that inference questions, unlike other types of questions, don\u2019t lend themselves well to prediction. Trying to guess the correct inference being drawn from several sentences worth of statements is generally a waste of time. Your best bet in approaching LSAT questions that ask for inferences is to use process of elimination, just as you would in sentence correction. Eliminate answers that are just \u201ceducated guesses,\u201d answers that aren\u2019t necessarily true, answers that are too extreme, and of course, anything irrelevant. Your answer will be the one choice that follows strictly from the statements in the question.
    \n 
    \n

    Sample Inference Question<\/h3>
    <\/div><\/div><\/div>
    \n\t
    \t\t

    \nSix Feet Under Corporation has two divisions, both of which performed consistently over the last five years. The Cremation Services Division accounted for approximately 30% of the corporation\u2019s transactions and 50% of the corporation\u2019s profits; the Poisonous Cleaning Supplies Division accounts for the balance.
    \nThe statements above support which of the following inferences about Six Feet Under Corporation over the last five years?<\/p>\n

      \n
    1. Measured in dollars, the total profits for Six Feet Under Corporation have remained stable over the last five years.<\/li>\n
    2. Cremation Services is an increasingly competitive field, while Poisonous Cleaning Supplies are a largely untapped market.<\/li>\n
    3. The Poisonous Cleaning Supplies Division yields a lower average profit per transaction than does the Cremation Services Division.<\/li>\n
    4. Six Feet Under Corporation\u2019s Poisonous Cleaning Supplies line has remained consistent over the past five years.<\/li>\n
    5. Most families will, over a given five-year period, spend more money on Cremation Services than on Poisonous Cleaning Supplies.<\/li>\n<\/ol>\n

      \n<\/div><\/div>
      \nOnly one of these answer choices MUST be true; let\u2019s take a look at the options:<\/p>\n

        \n
      1. We only know about percentages, or proportions, so we can\u2019t draw inferences about dollar amounts.<\/li>\n
      2. No information is provided about competition for either Cremation Services or Poisonous Cleaning Supplies.<\/li>\n
      3. This is the correct choice; Cremation Services has a profit to transactions ratio of 50%:30%, or 5:3, while Poisonous Cleaning Supplies has a ratio of 50%:70%, or 5:7. Therefore, the Poisonous Cleaning Supplies Division is doing more than twice as many transactions as the Cremation Services Division, but yielding the same profits.<\/li>\n
      4. Product lines are not discussed, and therefore can\u2019t be the subject of an inference.<\/li>\n
      5. Per-family spending is never mentioned, so we can\u2019t infer anything about it.<\/li>\n<\/ol>\n

        There\u2019s a pattern here: if it\u2019s not mentioned, an inference can\u2019t be drawn about it. Inferences MUST be supported by the evidence provided; remembering this one concept will give you a solid start in conquering inference questions on the LSAT.
        \n

        Logical Reasoning Assumptions<\/h3>
        <\/div><\/div><\/div>
        \nLSAT logical reasoning questions often ask you to identify the assumption of an argument. The first step in doing that successfully is understanding what, exactly, they mean by \u201cassumption.\u201d An assumption in LSAT-speak is the unstated link somewhere in the chain of evidence and conclusion. Finding the assumption means, basically, finding that gap in the argument and filling it.
        \nAssumptions can be roughly divided into \u201cnecessary\u201d and \u201csufficient,\u201d<\/a> and your approach to tackling an assumption question depends in part on which kind of assumption you\u2019re dealing with. A necessary assumption MUST be true in order for the conclusion to follow logically based on the evidence presented.
        \n

        Sample Assumption Question<\/h3>
        <\/div><\/div><\/div>
        \n\t
        \t\t

        \nIsaac wears glasses. Isaac also gets A\u2019s in algebra. Therefore, Isaac must be intelligent.
        \nWhich of the following assumptions is necessary to support the conclusion above?
        \na) Isaac gets good grades in all of his math classes.
        \nb) All boys named Isaac are smart.
        \nc) Isaac wouldn\u2019t wear glasses if he wasn\u2019t smart.
        \nd) Some people who get A\u2019s in algebra are smart.
        \ne) Everyone who gets an A in algebra is smart.<\/p>\n<\/div><\/div>
        \n

        Evaluating the Answer Choices<\/h4>
        <\/div><\/div><\/div>
        \nHere, you\u2019re looking at finding the unstated idea that MUST BE TRUE in order for the argument to work logically. Now, a few of these choices support the argument\u2019s conclusion. But only one of them is actually necessary to the argument. Let\u2019s looks at them one at a time.
        \na) Isaac gets good grades in all of his math classes.<\/i>
        \nThis isn\u2019t an assumption of this argument at all. Isaac\u2019s other math classes are outside the scope of the argument, since they are addressed in neither the evidence nor the conclusion.
        \nb) All boys named Isaac are smart.<\/i>
        \nThis choice would certainly support the conclusion; if this were true, then the conclusion would HAVE to be true. But is this statement NECESSARY to the conclusion? No. Other boys named Isaac don\u2019t have any necessary significance to this argument. So this is not a good choice.
        \nc) Isaac wouldn\u2019t wear glasses if he wasn\u2019t smart.<\/i>
        \nAgain, this choice would be SUFFICIENT to make the argument\u2019s conclusion follow from the evidence. \u00a0But is it necessary? No. So we\u2019ll bypass this one.
        \nd) Some people who get A\u2019s in algebra are smart.<\/i>
        \nThis is the correct choice, because it MUST be true in order for the evidence to follow logically from the conclusion. What if this wasn\u2019t true, and no one who got an A in algebra was smart? If that were the case, then the conclusion would not be true, based on the evidence that Isaac gets A\u2019s in algebra.
        \ne) Everyone who gets an A in algebra is smart.<\/i>
        \nOnce more, this choice is sufficient to support the conclusion, but it\u2019s not necessary. \u00a0So it\u2019s not the correct answer to the question that is being posed.
        \nNow, hopefully you noticed that the correct answer here is the least extreme relevant statement. That doesn\u2019t always have to be the case, but for questions that ask for necessary assumptions, it\u2019s a good general guideline. Be wary of answer choices that are extreme; they will often be sufficient, but not necessary, and will therefore trick test-takers who aren\u2019t careful in evaluating what exactly the question has asked them to find.
        \nBut what if the question paired with that argument looked more like this?
        \nWhich of the following assumptions, if true, best supports the conclusion above?<\/i>
        \nWell, in that case, the answer choices would look more like these:
        \na) Isaac gets good grades in all of his math classes.<\/i>
        \nb) All boys named Isaac are smart.<\/i>
        \nc) Isaac gets A\u2019s in his geometry class.<\/i>
        \nd) Some people who get A\u2019s in algebra are smart.<\/i>
        \ne) Some people who don\u2019t wear glasses are smart.<\/i>
        \nJust as in the last example, choice a) is not relevant to the argument as an assumption. But here, choice b) is the correct answer, because if that statement is true, then the conclusion is absolutely true. Choices c) and e) are irrelevant in the same way that choice a) is, since physics and people who don\u2019t wear glasses aren\u2019t at issue here. Now, choice d) is NECESSARY to the argument, but it is not the BEST support to the conclusion. Even if it IS true that some people who get A\u2019s in algebra are smart, that\u00a0doesn\u2019t guarantee that Isaac is.
        \n
        <\/span><\/span><\/div>
        \n