A student inquired recently about how to best understand the right and wrong answer choices in Weaken EXCEPT and Strengthen EXCEPT questions, and I thought my reply might help others here struggling with the same issue.
Here's my explanation:
The short answer is that that Weaken EXCEPT question is NOT the same as a Strengthen question, and it’s crucial that you treat them differently! Let me explain why.
A little background first.
When you see a question like Weaken EXCEPT in Logical Reasoning, or something like Must Be True EXCEPT in Logic Games, it’s important to recognize the nature of the correct vs incorrect answers. Because of the except in the question, what they’re really describing is what the four wrong answers will be: Weaken EXCEPT means the four wrong answerswill all weaken, Strengthen EXCEPT means the four wrong answers will all strengthen, and so on.
I imagine that part is pretty straightforward, but it leaves us in an interesting position with the right answer. What’s the correct answer choice going to do in a Weaken or Strengthen EXCEPT? The answer is that it will be the exception: if four weaken, then the single right answer exception simply won’t weaken. If four strengthen? Same thing, where a single choice will be correct because it doesn’t strengthen the argument.
And now we get to the real heart of your question, I think: what does it mean to “not weaken” or “not strengthen”?
The key here is something called logical opposition. What’s the logical opposite of, say, “hot”? A lot of people would say “cold,” but that’s something called polar opposition, where you have pairs in extremes (up/down, tall/short, etc). Logical opposition, which is what the LSAT tests, is softer and more all-encompassing than that. In logical opposition the opposite of “hot” is just “not hot.” That includes cold, of course, but also every other temperature that isn’t hot: lukewarm, freezing, and all the rest.
So what’s the logical opposite of “Weaken”? Again, many people would incorrectly say “Strengthen,” but that’s polar. The logical opposite is just “Not Weaken.” That includes Strengthen at the other end of the spectrum from Weaken, but it also includes ideas like Neutral and Irrelevant. As long as it doesn’t hurt the argument it’s correct. So the correct answer choice for Weaken EXCEPT can be anything from an extreme like strongly supports/strengthens to a middle-ground irrelevancy that does absolutely nothing to the author’s argument. And it’s that neutral answer type that the test makers love!
Ditto, of course, for Strengthen EXCEPT: the right answer could weaken, but it could also completely miss the point of the argument and be irrelevant, or add information that has no effect whatsoever. Again, as long as it doesn’t help it’s fine.
So be super careful not to treat Weaken EXCEPT like Strengthen, or Strengthen EXCEPT like Weaken! Doing so would miss the possibility of answer choices that don’t impact the argument at all, which in the case of EXCEPT questions aren’t just correct, but generally preferred by the test makers.
I hope that helps to clarify things!