## Sufficient vs. Necessary Assumptions

FK00144
LSAT Apprentice

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pg. 5-1 in the course book

is sufficient and necessary assumption related to the sufficient and necessary in conditional reasoning or is it just referring to the answer choice being sufficient/ necessary for the conclusion to be drawn?
Dave Killoran
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FK00144 wrote:pg. 5-1 in the course book

is sufficient and necessary assumption related to the sufficient and necessary in conditional reasoning or is it just referring to the answer choice being sufficient/ necessary for the conclusion to be drawn?

It's both actually! The nature of the answer choice (in relation to the conclusion) is reflective of those conditions. Does that make sense? It should after the lesson, but if not, let us know!
Dave Killoran
PowerScore Test Preparation
My LSAT Articles: http://blog.powerscore.com/lsat/author/dave-killoran
James Finch
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Hi FK,

Absolutely! The difference is that Sufficient Assumptions (Justify Questions) can act as sufficient conditions to the conclusion's necessary condition: if the sufficient assumption is true, then the conclusion must be true. This makes them a bit easier to deal with than Necessary Assumptions (Assumption Questions).

Necessary assumptions act differently, in that they are necessary to the argument in the stimulus, but not sufficient to make it true. This means that the conclusion is the sufficient condition, while the assumption would be the necessary condition. This requires us to use the Assumption Negation technique (essentially the contrapositive) to test whether an answer choice is really necessary to an argument or not.

To recap, the logic behind a Sufficient Assumption looks like:

Assumptiontrue Conclusiontrue

while a Necessary Assumption would diagram to:

Conclusiontrue Assumptiontrue

requiring us to use the Assumption Negation technique (the contrapositive) to test for the correct answer choice:

Assumptiontrue Conclusiontrue

Hope this clears things up!