Conditional Reasoning

[anamank]

I have purchased about 6 PowerScore books now and I think they are all great!

I have kind of a stupid question, and it refers to conditional reasoning. I know that when conditional reasoning is mixed with a must be true question, one must always search for a repeat form or contrapositive. Now, when it comes to justify the conclusion questions, strengthen, weaken, or anything for that matter that has conditional reasoning in the stimulus, I am wondering what the correct way to go about it is. Basically, if there is conditional reasoning in the stimulus of a justify the conclusion question, you only need to look for the answer choice that adds a piece of information to the stimulus that logically proves the conclusion... right? So one doesn't need to worry about contrapositives or anything like that (unless it is a must be true question) because it does not apply to these questions?

And for weaken ones, find one that weakens the conclusion? Contrapositive and repeat forms are irrelevant?

Does that make sense?

Thanks

[Nikki Siclunov]

When do you need the contrapositive? Potentially every time you encounter an argument containing conditional reasoning. The contrapositive is an inherent inference deducible from any conditional statement. As such, it is always relevant and potentially applicable to solving any question whose stimulus contains conditional reasoning.

When the stimulus contains a single conditional statement followed by a Must Be True question stem, the correct answer choice will usually be in the contrapositive form of that statement. However, if the stimulus contains multiple conditional statements, your job tends to involve creating conditional chains (which may use the contrapositives of some of these statements, if needed), based on which you can make additive inferences that prove the correct answer choice.

When it comes to Justify questions, indeed you are looking for an answer choice that adds a piece of information to the stimulus that logically proves the conclusion. However, such an answer choice may be given in the contrapositive form. The contrapositive can also be useful in connecting the conditional statements in the stimulus. For example:

You will get a high LSAT score only if you study hard. However, you will not study hard unless you are willing to ruin your social life. Therefore, getting into Harvard Law School requires the willingness to ruin your social life.

To justify this conclusion, you need to create the following chain:

Premises: High LSAT score --> Study Hard --> Ruin Social Life

Conclusion: HLS --> Ruin Social Life

To justify the conclusion, you need to establish that getting into HLS requires a high LSAT score (HLS --> high LSAT score). This idea can be presented in multiple ways:

If you don't get a high LSAT score, you will not get into HLS (contrapositive).
All HLS admits need a high LSAT score.
Unless you get a high LSAT score, you will not get into HLS.
Only those with high LSAT scores will be admitted into HLS.

As you can see, the contrapositive is relevant to any argument involving conditional reasoning, including those containing multiple conditional statements. It can also be the form in which the correct answer is given, whether or not you are dealing with a Must Be True question. Among the question types most likely to contain conditional reasoning are Must Be True, Justify, Parallel, Flaw, Assumption, though it is possible to encounter it in other question types as well. Of course, you need not diagram every stimulus in which you encounter conditional reasoning: make a diagram whenever you see the need for one (e.g. you are dealing with multiple conditional statements that form a conditional chain).

When it comes to Weaken questions with conditional reasoning stimuli, the approach is slightly different: look for an answer choice that undermines the necessary condition in the stimulus. If you can show that the necessary condition is not required for the sufficient condition to occur, you will effectively weaken the conditional relationship underlying the conclusion. Typically, however, Weaken and Strengthen questions contain causal (not conditional) reasoning.