Tag Archive: But not both

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LSAT Logic Games: How to Use ‘But Not Both’

In Logic Games, cute and cuddly “A must come before B” rules are often treated as cherished instructions. It makes sense; they’re simple, absolute, and easily diagrammed. They’re also more intuitively digestible than some of our more complex Logic Games rules.

But digesting complex carbs gives you fuel, while simple carbs give you a beer belly. Similarly, complex LG rules often unlock the game and propel you through the questions, whereas “A before B” rules… make you fat… (shush, no analogy is perfect).

One of the most useful complex relationships comes in the form of an exclusive disjunction. You remember these from Logical Reasoning: “Bubba buys either laundry detergent or a whole new wardrobe, but not both.”

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Logic Games: Scary “But Not Both” Rules

In early 2007, the Law School Admissions Council (LSAC) introduced a type of rule to Logic Games that had legions of test-takers running home to mommy. It was particularly egregious because of the way in which it was introduced. Students initially thought that it was an easy, 1:1 correspondence game. But then everything went horribly wrong with three little words: but not both.

Whereas most students can readily cope with diagramming “A comes before B”, or “C comes before D”, what do you do when the rule states “A comes before B, or B comes before C, but not both”? (Other than cry and reach for a binkie, that is).