Normally, assumption is something that must be true in order for the conclusion to be true, which is a necessary condition.
But sometimes the stem says：the conclusion is properly drawn if which one of the following is true. According to Kaplan, these seem to be assumption questions as well. Does this make the assumption a sufficient condition , and kinda like a strengthener?
Thanks!

the type of question you mentioned is sufficient assumption question. kaplan does not distinguish sufficient assumption and necessary assumption.
sufficient assumption functions as strengthener, it has very strong strengthening force, it actually proves the conclusion valid, together with the premises

This is the important part - we're not looking for something that just simply strengthens the argument. It has to strengthen it all the way to valid. You can view it as a Strengthen+ question, because you need it to be bulletproof after the sufficient assumption (since the SUFFICIENT assumption is ENOUGH to make it valid).

A necessary assumption is like a lifejacket, in that it is necessary just to keep the argument above water, and without it, the argument would entirely collapse. The necessary assumption merely makes it POSSIBLE for the conclusion to follow (since there may be a million more necessary prerequisites to reach a given conclusion).

A sufficient assumption is one that, if inserted into the argument, GUARANTEES that the conclusion will be true. It makes the argument entirely airtight and bulletproof. Once that sufficient assumption is added in, you have no choice but to reach the given conclusion. Whereas the necessary assumption merely makes the conclusion possible, a sufficient assumption makes it inevitable.

I concur with all previous responses - everyone nailed it.

Here's an important reason to know the difference between necessary assumption and sufficient assumption questions:

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