Conditional mantras

  • April 13, 2017 at 2:50 pm #3055
    Alexandra
    Participant

    I dont understand how to diagram unless, it gives us examples on page 256 but im still confused. thank you

  • April 17, 2017 at 4:01 pm #3057
    Mike Kim
    Keymaster

    Hi Alexandra —

    “Unless” is a tough phrase to understand intuitively, and even those who practice for the LSAT for a long time often need to pause to carefully consider and understand unless statements correctly —

    Whenever you run into a conditional statement, you want to think about what it actually means, consider the guarantees it presents, and then notate those guarantees —

    To get what the word “unless” means on a conceptual level, it’s easiest to use a statement that’s true in life and easy to remember, such as

    “Unless you are in California, you can’t be in San Francisco” —

    Two natural ways that people tend to understand the conditional guarantees inherent in the above statement are that the phrase above means —

    “If you are not in California, you can’t be in San Francisco” [/C -> /SF]

    And

    “If you in San Francisco, you must be in California.” [SF -> C]

    Either is great and both are correct ways of understanding the consequences of unless statement (notice they are contrapositives of one another) —

    So, when you run into an unless statement on the exam, ideally,

    a) you want to try and handle it the way would any other conditional, which is to try your best to understand it and the guarantees it offers, then notate those guarantees.

    And then, if you can’t see that clearly using the default methods,

    b) you want to be practiced at, and, able to refer to, certain analogous relationships (what I call mantras in the book) that can help you understand the situation at hand correctly.

    So, for example, if you run into the statement

    “X can’t be selected unless Y is selected”

    — and maybe you don’t feel confident making the call as to whether this means X guarantees Y or Y guarantees X, etc. —

    You can say to yourself an analogous mantra that has a very similar unless phrasing structure, something such as,

    “You can’t be in SF unless you are in California.”

    This gives us SF -> C, /C -> /SF

    and so, going back to the initial statement, we know

    “X can’t be selected unless Y is selected” must mean the equivalent of

    X -> Y & /Y -> /X

    (if x was selected, y must have been selected, just like if you are in SF you are in California & If y was not selected, x must not have been selected, just like if you are not in California you cannot be in SF.)

    It can take some practice to get used to using these methods, but they can be remarkably effective once you get comfortable with them.

    HTH — Mike

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