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LSAT Preptest 154, Section 1, Question 26

"Philosopher: A person is morally responsible for…"

Explanation

This is a formal logic question. We are given some rules and asked to follow them.

Morally responsible >> Action performed freely
Action performed freely >> Alternate action genuinely open
Alternate action genuinely open >> Alternate action is not morally wrong

We are generally going to have to link these up, looking for a statement that a person is morally responsible only if the alternate action is morally wrong. Or the contrapositive thereof. The "must-be-true" questions almost always go for the most distant possible inference.

A.  Not morally responsible >> No alternate action genuinely open

  • Remember, unless means “if not.” It negates the clause and indicates a sufficient condition. This is not a valid inference, the sufficient condition is that something is morally responsible, not that it isn’t. No inference comes from an action not being morally responsible. The contrapositive yields, if an action is genuinely open the action is morally responsible. This cannot be inferred, it goes the wrong way up the arrows and makes a converse error.



B. This is not really a conditional that is derived from the prompt. It basically says that any person who performs any action, genuinely open, performed freely, or otherwise, is mostly not morally responsible. This is not an inference of the type that we can make with our information.


C. Alternate action genuinely open >> Morally responsible

  • This is a converse error, going the wrong way up the arrows.


D. Alternate action is morally wrong >> Alternate action genuinely open

  • We’re getting a little weird with it, this is the negative of a negative term. But, this misses the mark, it fails to negate the sufficient condition “alternate action genuinely open” as required to find a contrapositive.


E. (Correct Response) Alternate action morally wrong >> Action is not performed freely

  • This is the contrapositive of the second and third rules. It is therefore a valid inference. To demonstrate, we reverse and negate. Action is performed freelyàAlternate action is not morally wrong. We just skip over alternate action is genuinely open. This is legal because of the transitive property. A >> B >> C means A >> C.

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