I think the distinction here may just be one of semantics. I would call the arguments “potentially” flawed, or alternatively, “incomplete.” However, by those terms, I’m confident that I mean exactly what Mike means when he says “flawed” (confident because Mike and I have spend many hours discussing the LSAT). The reason I emphasize the distinction is because I think it will be most helpful to you to be clear. To call an argument “flawed” might suggest that it’s a bad argument, or one that leads to a factually incorrect conclusion. But in the case of assumption-based argument (in LSAT-speak, one that “takes for granted” or “fails to consider” something), that’s not necessarily the case. For instance, to get back to my example, the argument is “potentially flawed” in that it may be the case that some people can do well on the LSAT without studying. Or it’s “incomplete” in that it didn’t explicitly state that premise. But on the other hand, it could be that I have enough experience and knowledge to make that determination, and my analysis is factually correct, in which case it might be misleading to called it “flawed” in lay terminology. But yes, as Mike would suggest, it’s “flawed” in strict logic terminology in that the premises IN AND OF THEMSELVES don’t get you all the way to the conclusion.
I just don’t want you to have the impression that assumption-based arguments lead to bad conclusions. They don’t, at least not necessarily. What they lead to are not-completely-justified conclusions.
Even though it’s an imperfect argument when there’s a missing premise, it’s not “flawed” per se in the way that an argument like “All cats are mammals. Fluffy is a mammal. Therefore, Fluffy is a cat” is flawed. Here, we have a clear misunderstanding of the relationship between cats and mammals, and the route between the premises and the conclusion isn’t just incomplete; it’s flat-out wrong.
As I tried to suggest in my original response, though, the distinction on assumption questions isn’t really critical. You don’t have to worry about overstepping the line, because if you understand what’s missing from the argument, you’re going to get the question right whether it’s an assumption question or a flaw question. It’s not really about the question type here; it’s about the argument structure. The real question is what way of looking at it is the most helpful to you. In your original post, it sounded like you had some confusion through sensing (correctly) that an assumption can be ACCURATE, and that’s what it seems like you original question was asking, and why I was trying to elaborate a bit. Based on what you’ve been asking and what you seem to understand, maybe the simplest way I’d try to wrap it up would be something like this –
1) An assumption can be correct, and it can be justified, so it’s not “flawed” in the sense that it’s necessarily factually wrong.
2) BUT, an argument that relies on an assumption is at the very least incomplete; there’s always that degree of uncertainty. IS the assumption, in fact, true?
3) For LSAT purposes, that answer to the question in 2), above, doesn’t really matter – the (at least POTENTIAL) problem with the argument is the missing piece. If you recognize and focus on that, you’ll get the question right, whether it’s an assumption question or a flaw question.
The “degree of uncertainty” I’m talking about above is related to what Hume called “The Problem of Induction.” Conclusions based on observation are always at least potentially wrong. Take these two situations, for instance:
1) An alien lands on earth. The next morning, the alien sees the sun rise in the east and set in the west. This happens ten more times, and the alien concludes that on earth, the sun always rises in the east and sets in the west.
2) An alien lands on earth and finds someone teach him/her/it about how we record time on earth. It’s March, and the alien learns that there are 31 days in March. Then the alien learns that there are 30 days in April. For 9 more months (the same number of observations in 1)), the alien finds that there are 30 or 31 days in each month. The alient concludes that all months on earth have at least 30 days. Then it becomes February. OOPS. That’s Hume’s “problem of induction.”
There’s always the potential that it’s 2). That there’s a student I haven’t met who scores well on the LSAT without studying, for instance, in my example. But again, as long as you’re aware that this MIGHT be the case, it doesn’t matter (on the LSAT) whether it actually IS the case. You just have to identify the gap in the argument.