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#25 - Marianne is a professional chess player who hums

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Could someone clarify why C is incorrect? Also, how would we diagram this answer choice for more clarity? I always have trouble diagramming 'Not all' statements, because it implies none or some. Thank you!
PowerScore Staff
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Hi kcho,

"Not all" is really a term reserved for formal logic which is tested very little on the modern LSAT. Formal logic includes less-than-certain terms, such as "some," "most," "usually," "not all," etc...

Everything that you know about diagramming conditional logic can be applied to formal logic, but make sure to take a lot of care with making connections between terms in chain relationships and taking the contrapositives of formal logic statements (there is no contrapositive when a formal logic statement uses the term "not all" or "some" or "most".0

With that not, let's look at the stimulus. Marianne's argument goes:

unaware :arrow: involuntary :arrow: responsibility

Answer Option (C) pulls this bs Shell Game with it's logic by saying involuntary (not all) :arrow: unaware.

See the difference? If it had been the other way around, that would attack the first sufficient in Marianne's argument and that would effectively weaken her argument, but instead it's reversing the logic which does not effect the conditional argument she's making. That's why it's wrong.

Thanks for the great question and let us know if this helped!
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Unaware → Involuntary → Not Responsible

So Answer (D) is taking the conditional statement above and showing that the necessary condition (involuntary) is not met, thus weakening the statement?

To clarify for Answer (C), do I read this as conditional or formal logic? I always get confused on these!
Involuntary → Aware or
Involuntary (Not All) → Unaware (Mistaken Reversal)
Francis O'Rourke
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Answer choice (D) tells us Marianne can, with some amount of effort, become aware of her humming and can control it. I understand a "controllable" action as the opposite of an involuntary one, so this answer choice tells me that Marianne could get rid of both the sufficient conditions that led her to believe that she should not be held responsible for her action.

Answer choice (C) tells us that it is not true that ALL involuntary actions are ones which you are unaware of.
That is, involuntary :arrow: unaware is not always true.

We can also diagram that statement as involuntary :longline: some :arrow: aware .