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If the question stem is "The argument's conclusion is properly drawn if which one of the following is assumed?"

I'm pretty sure i should pick a sufficient condition, am i correct? or the correct answer can be a necessary condition sometimes?

Sufficient.

yea, but i feel that in PT 60, Question 22. The right answer is a necessary, but not sufficient.

mz253 wrote:yea, but i feel that in PT 60, Question 22. The right answer is a necessary, but not sufficient.

The right answer is sufficient. The argument concludes that the invention of money occurred independently in more than one society. It provides evidence that money is in every society and that it must be invented to exist. The right answer says that some societies are isolated enough not to be influenced by others. If they're isolated (as the right answer says), and if they have money (as one of the premises says that they do), and if money must be invented to exist (as one of the premises says), then money must have been invented independently there (as the conclusion says).

On the other hand, the right answer is not truly necessary. Even if all societies are influenced somewhat by each other, they may not have been influenced in this particular way, and may have invented money independently, or they may have been influenced only in the recent past, after their inventions of money. Even if that answer weren't true, the argument could still stand, so it's not necessary to the argument.

Part of the confusion may come (in other questions) from the fact that some conditions are both necessary and sufficient. Filling in all the right bubbles on the LSAT scantron is both necessary and sufficient for getting a perfect score, for example.

Thanks! You are a great teacher!