Just kidding, obviously.
Yes, you do need to be able to diagram ---
But you SHOULDN'T diagram for all question-types!!!
Quick sidenote on that:
Some people are big on diagramming. I think it's useless for informal logic questions, which are MOST of the Logical Reasoning section!
When I DO diagram, it's for *some* Must Be Trues/Most Strongly Supporteds, *some* Sufficient Assumptions, and *some* Parallel Reasonings.
******
Today, I'll focus on Sufficient Assumptions, since that's what the 1st - more significant - question was about.
Like I said, these are one of the few question-types often worth diagramming.
I think of Sufficient Assumption Qs as providing information that, if true, would be sufficient to guarantee the argument's validity.
In other words, this information, if true, will guarantee the conclusion's validity.
In a general sense, the most common formats for these questions, are (in order of complexity):
1. restatement of conclusion / argument
2. contrapositive of conclusion / argument
3. the format I'm about to share with you (called linking conditions)
I've found this 3rd format to be the most common. (Click here for a big list of Sufficient Assumption questions in each of these formats.)
I'm going over the most common format with formal logic, then with a few examples from real PT questions:
Evidence: D ---> E
Conclusion: D ---> F
Sufficient Assumption #1: E ---> F
Sufficient Assumption #2: NOT F ---> NOT E
Why does this work? Because if we take our evidence, "D ----> E" and combine it with our Sufficient Assumption "E ---> F", we get a longer chain D ---> E ---> F that fully guarantees our conclusion, "D ---> F."
Cool, huh?
When I first discovered this, it completely blew my mind!
The contrapositive's a bit tougher to understand, so let's take a look at it:
Evidence: A ---> B
Conclusion: C ---> B
Sufficient Assumption #1: C ---> A
Sufficient Assumption #2: NOT A ---> NOT C
Why does this work? Because if we take our evidence, "A ----> B" and combine it with our Sufficient Assumption "C ---> A", we get a longer chain "C ---> A ---> B" that fully guarantees our conclusion, "C ---> B."
Now, why doesn't A ---> C work?
Well, let's try it:
If we take the evidence A ---> B and add the Sufficient Assumption A ---> C, all we get is that A requires both B and C. It does nothing to tell us that B and C are conditionally or directly related to each other.
Here are the steps to take to use these formulas:
Make either the:
sufficient conditions of the evidence and conclusion identical (as with the example involving D, E, and F)
or
necessary conditions of the evidence and conclusion identical (as with the example involving A, B, and C)
Then, imagine each of those evidence-conclusion diagrams as a big circle and link the parts that are different going CLOCKWISE.
For the first example (with D, E, and F), you get: |
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| Cool, huh?
Very truly yours,
Sufficient Assumin' Steve
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2. Logical Reasoning Explanations
The explanations that should have come with the LSAT. These don't just fall back on "out of scope," but actually tell you why the wrong answers are wrong, why the right answers are right, and the easiest way to get the correct answer.
3. Logical Reasoning Cheat Sheet
Based on what I'd typically do in college: read what the professor emphasized and condense it all onto a single piece of paper. It gave me a quick reference, making things a lot less threatening and a lot more manageable.
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