Ch. 15 Diagramming Review Exercise Coahces picking Varsity and JV Players

    • November 6, 2017 at 7:02 pm #3338

      I’m working on the exercise in Ch. 15 about the coach choosing players for the varsity and junior varsity team, and I’m stuck on how to properly infer the last rule which reads, “If Tim is selected for junior varsity, then Wilma will be selected for varsity.” When I diagram this rule, and create the contrapositives, it seems to me that this rule should logically deduce to Tim and Wilma not being allowed to be on the same team. Here’s how I figured this:

      If TJV -> WV
      If W not V -> T not JV
      Since these players can only be either V or JV, I know that if a player is not on varsity, then the player will be on JV, and vise versa. So, then I continue to deduce this rule as such:

      If WJV -> TV, which essentially means they are never on the same team together.

      How is this inference incorrect?

      When trying to answer question number one on this exercise, upon realizing that W would end up on varsity, I also believed that that would mean T has to be on junior varsity. But, apparently this was not a possible conclusion, as the correct answer for this question says that T being on JV is not definite, and indeed, “could be false.” Please tell me what I’m missing.

    • November 7, 2017 at 11:02 am #3339
      LSAT Dan

      Hi, Emily (not Emily from Reddit, are you?). What you’re missing is that although it’s true they can’t both be on the JUNIOR varsity, nothing about the rule says that they can’t both be on varsity. Imagine this partial layout:

      Varsity: Tim, Wilma.

      Now consider the rule: “If Tim is selected for junior varsity, then…”

      Well, Tim ISN’T selected for junior varsity; therefore, the rule doesn’t apply to this situation.

      A good general rule is that a single conditional rule (not an “if and only if” rule” cannot control all possible outcomes. In other words, by itself, one conditional can’t force two variables to the same side, or keep them separated.

      Hope this helps.

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