June 2008 LSAT Section 2 Question 5

Byrne: One of our club's bylaws specifies that any officer who fails to appear on time for any one of the quarterly ...

Zacfisch on March 30, 2020

Could you explain why C is wrong in this example?

Is it with the wording of the question because it seems like the argument confused a necessary condition for being sufficient?

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Victoria on March 30, 2020

Hi @Zacfisch,

Happy to help!

Byrne concludes that Thibodeaux must have been late for a quarterly board meeting.

Why? Because Thibodeaux is an officer who was recently suspended and the club's bylaws state that any officer who misses two monthly general meetings or is late for a quarterly board meeting must be suspended.

Late QBM OR Miss 2MGM - > S
Not S - > Not Late QBM AND Not Miss 2MGM

Byrne notes that Thibodeaux has never missed a monthly general meeting and uses this information to draw the above conclusion.

What is the flaw in reasoning here?

Byrne assumes that there is no other reason for which Thibodeaux could have been suspended. This is directly restated by answer choice (B):

"[Byrne] presumes, without providing justification, that if certain events [Late QBM or Miss 2MGM] each produce a particular result [S], then no other event is sufficient to produce that result."

You are correct in that Byrne seems to be working backwards from the necessary condition to conclude that Thibodeaux must have been late to a quarterly board meeting. However, answer choice (C) talks about an assumption, not a condition.

In drawing the conclusion that Thibodeaux must have been late to a quarterly board meeting, Byrne assumes that there is not other reason that Thibodeaux could have been suspended. This is the flaw in reasoning, not that this assumption was actually sufficient instead of necessary.

A mistaken reversal would have said that Byrne takes for granted that a condition required to establish the conclusion is sufficient to establish that conclusion i.e. mistaking the necessary for the sufficient condition.

In short, (C) is incorrect because of the use of the word 'assumption.'

It's a bit of a tricky distinction and I hope I've explained it well enough for you.

Please don't hesitate to let us know if you need any further clarification.

Zacfisch on March 31, 2020

Perfect! Thank you!

Ravi on April 12, 2020

@Zacfisch, let us know if you have any other questions!