p. 392, question 2 — typo, or I'm missing something in the answer

    • June 10, 2017 at 8:31 am #3116

      Hey Mike/all,

      In working through Lesson 27, I came upon a question for which I can’t reason the correct answer. Page 392, question 2, asks for (essentially) a rephrasing of a rule for the game.
      The rule for the game is: “If F is not played, L will be.”
      The question asks what rephrasing would have the same effect on the order of songs. The correct answer, according to the solutions, is: “Either F or L is played.”

      However, I can’t see why the band can’t play both. I get that [not F = L] and [not L = F], but couldn’t both of these be played with no problem? There are no overarching game restrictions I can see that prohibit both from potentially being played.

      The answer I had chosen is (B): “They will play F only if they don’t play L.” Am I wrong that this phrasing means [not L = F]? If so, I really can’t figure out what I’m missing with this question.

      Thank you so much for the help!

    • June 10, 2017 at 1:09 pm #3117
      LSAT Dan

      Ariana –

      The word “or” can be either “inclusive” or “exclusive.” That is to say, sometimes, it includes the possibility of both:

      “It would be nice to have a Ferrari or a Porsche” doesn’t mean that wouldn’t be nice to have a Ferrari AND a Porsche. That’s the “inclusive” or – it means “At least one.”

      On the other hand, contrast this with:

      “Please put two packets of Sweet & Low or sugar in my coffee.” We can safely infer that I don’t want two packets of Sweet & Low AND two packets of sugar in my coffee. Unlike the Ferrari/Porsche example, in this case, it means “Exactly one.”

      On the LSAT (which is to say, when dealing strictly with the logical context), “or” is always inclusive *unless you’re told otherwise, or the context makes the inclusive “or” impossible.* That’s why you’ll see, in certain logic games, rules like “The blue team includes Rob or Jeff, BUT NOT BOTH.” (emphasis added). If it didn’t say “but not both,” then it would be fine to put Rob AND Jeff on the blue team. In other words, “or” really means “and/or.”

      I said that sometimes context makes that impossible. Let’s say we have a sequencing game involving a race, and there’s a rule that says, “Kim finishes in first place or third place.” Obviously, she can’t finish in both 1st place AND 3rd place, so by context, we have an instance of the exclusive “or.”

      SO, getting back to your question, the answer “either F or L is played” is correct; however, you’re also correct in noting that they could BOTH be played. When Mike says either F or L is played, that doesn’t preclude the possibility of both. It’s the inclusive “or,” which it always is, unless it can’t be, or you’re told otherwise. So it’s one, or the other, or both being played. All of which is covered by the statement “F or L is played.”

      Going back to your other question, yes…you’ve mistranslated (B). You’ve symbolized it exactly is if the word “only” were not in the sentence. The first thing I tell any LSAT class is that the most important word on the LSAT is “only.” Perhaps the simplest way to look at its effect is that “only” negates both sides of a conditional relationship. So the fact that the word “only” is there means that (B) isn’t:

      NOT L –> F


      L –> NOT F

      One way to see this a little more clearly is to keep the structure of the statement while substituting content that you’re familiar with. For instance, passing the bar exam is a requirement of practicing law. So let’s use “practice law” instead of F, and “fail the bar exam” instead of L. Now, (B) would read:

      “(She) will practice law only if she doesn’t fail the bar exam.” That’s a true statement. But now let’s look at the way you translated it:

      “If she doesn’t fail the bar exam, she will practice law.” (Not L –> F). That’s no longer a true statement. She might pass the bar exam and go on to medical school. Or pass the bar exam but then fail the background check. Or fail to pay her bar dues. Passing the bar exam isn’t a guarantee of lawyerdom. But look what happens when you negate both sides:

      “If she DOES fail the bar exam, she will NOT practice law.” Yup. That’s the one we want.

      So basically, you got it half right – you translated the original statement correct; you just have to realize that the given correct answer agrees with you – “Or” is inclusive (except when…)

      But watch out for the word “only”; if it weren’t there, (B) would, indeed, be a correct answer. But the fact that it is there makes a world of difference.

      Hope this helps.


    • June 11, 2017 at 7:47 am #3118

      Dan –

      That makes total sense and is extremely helpful. Thank you so much for the quick reply (especially on a Saturday). I have now written your ‘only’ advice (above) on my short list of rules to remember (that I usually forget)… so here’s to hoping it stops tripping me up.

      Thank you again!


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