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General questions relating to LSAT Logical Reasoning.
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 sadjasmine
  • Posts: 6
  • Joined: Aug 06, 2022
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#98165
Is the supporter necessary assumption, the one that acts as a bridge, not the same thing as a sufficient assumption?
 Robert Carroll
PowerScore Staff
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#98208
sadjasmine,

Sometimes, but not always. Not all "bridges" between premises and conclusions will be identical. An argument both wants and needs a bridge between its premises and its conclusion, but that doesn't mean that every bridge is needed, nor does it mean that every bridge fully closes the gap and makes the argument perfect. A bridge between premises and conclusion that's needed by the argument would be a good necessary assumption. If it ALSO makes the argument perfect, then it's a good sufficient assumption. However, not everything necessary for the argument will suffice to make the argument perfect. So a bridge may be necessary but not sufficient.

Things can work the other way around, also. A particular bridge between premises and conclusion may make the argument perfect, and thus be a good sufficient assumption, but be stronger than necessary or include extraneous information, and thus go beyond what's necessary. Such a bridge would suffice for the argument, but wouldn't be needed.

It is possible that some bridges do both, and in these cases, it doesn't make much difference what the question type is. In the other cases I went over, however, it makes a big deal which question type we're dealing with, because a bridge necessary for the argument but not sufficient is a good answer for an Assumption question but not a Justify question, and a bridge sufficient to prove the conclusion of the argument but not necessary for it would be a good answer for a Justify question but not an Assumption question.

Robert Carroll

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