Flaw in the Reasoning, presupposition

[obs23]

I am an ESL student and I guess my questions make it look like...I do not know what Since LSAT is so nitpicky, so it looks like I am becoming one.

In the chapter of Flaw in the Reasoning, p.380, example of internal contradiction is cited:

"Everyone should join our country club. After all, it's an exclusive
group that links many of the influential members of the community."

and then one of possible ways to address the flaw is described as (I understand that it is used in general form, not necessarily pertaining to this question so pls do not hold me liable for it):

"the author makes irreconcilable presuppositions"

From the clarification standpoint, what, if any, presuppositions the argument above makes? If none are made, please provide an example (preferably from LSAT, I could look up the question) that draws on the notion of presupposition.

When I look at the dictionary I seem to understand what the word means, but it is truly difficult to reconcile my understanding of a word and the way LSAT views it. Is presupposition implied or explicitly stated? if it is implied, then is it any different from assumption?

Thanks for your efforts.
Obs

[Ron Gore]

Hi obs23,

A presupposition is a fact taken as true without support and then used in support of a conclusion. Since the LSAT is not a knowledge-based test, and we don't attack the truth of the premises given us in stimuli, you could say that all premises on the LSAT are presuppositions. There also may be facts an argument assumes, but are not written expressly in the stimulus, which are also presuppositions.

In the country club example, there's an express presupposition, that the club is "an exclusive group," and a presupposition that was not stated directly, but provides the rule applied to reach the conclusion that "everyone should join our country club." The rule would be something similar to "everyone should join an exclusive group..." That rule and the fact of exclusivity are irreconcilable, because the application of the rule destroys the exclusivity.

A example of this type of error from a released LSAT is Prep Test #20, October 1996 LR1 Section I, Question 22.

Thanks,

Ron

[obs23]

Really appreciate your view, very helpful Ron.

Obs

[Ron Gore]

You're welcome!