Flaw vs weaken

[cyt5015]

Dear LSAT geeks,
I noticed some subtle differences of selecting the right answer for Flaw question and weaken question.
For flaw question (causal), the correct answer can be: fails to consider the influence of alternative cause on effect (e.g. price rising); But this type of answer cannot be considered as a correct answer for weaken question, because the influence of alternative is unclear: it may lead to price rise or decrease.
Similarly, an answer which is correct for weakening may be an incorrect answer for flaw. PT 45, section I, Q20.
answer C is a weaken answer but not a flaw.
I am struggling to classify those types of answers especially under time pressure. Can you give some advice?

Thank you!

[ohthatpatrick]

Good question ... tricky, nuanced answer.

For starters, were you assuming that Flaw and Weaken were the same type of question/task?

It can be tempting to do so because there IS some overlap, but you shouldn't be surprised to see them act differently. They are, after all, different.

Flaw asks, "What's wrong with this argument?"

Weaken asks, "Which new idea I'm about to offer you would make this argument less believable?"

Those are two different tasks.

Although all Assumption Family questions have much in common, Flaw does have one critical distinction.

For all Assumption Family tasks, we read the argument, break down the core, and evaluate whether there are:
- missing logical links
- potential objections
- alternative explanations/interpretations

With Flaw we do all that, but we're ALSO attuned to
- illegal moves

Moves such as -
- circular reasoning
- correlation --> causality
- Nec/suff reversals
- attacking the source, etc.

As you've probably noticed, Flaw answer choices come in several different forms.

You have Necessary Assumption type answers:
takes for granted ...
presumes w/o providing justification ...
assumes without warrant ...

You have Weaken type answers:
fails to consider ...
neglects the possibility ...
ignores the possibility ...

But you also have purely descriptive answers (unique to Flaw):
- treats two things that coincide as though they have a causal relationship
- assumes what it sets out to prove
- infers, from the claim that a certain event is required for a condition to obtain, that the event would ensure that the condition obtain
etc.

Some "Flaw" questions are literally Nec Assump or Weaken, because the question stem actually packages in "takes for granted" or "fails to consider".

For example, if I see a question stem that says:
"The argument is vulnerable to criticism because it fails to consider that"
Then I really just think "Weaken", because each answer choice is prefaced by that Weaken language "fails to consider" and so all the answer choices will be giving me new ideas and testing me on whether they undermine the reasoning.

But on typical Flaw questions, the set of choices shifts back and forth between Weaken ideas, Necessary Assumption ideas, and purely Descriptive ideas.

So the only tweaks you probably want to make to your process in understanding Flaw (which is the more complicated, diverse question type) are
1. Don't just look for a way to Weaken a flawed argument. Try to describe WHY/HOW it's flawed, because many answers just describe the argument, they don't offer new objection ideas.
2. Make sure for any answer you pick that it passes this two part checklist:
- Did this happen? Did the author do what this choice says he did?
- Is this a reasoning flaw? Does this describe a problem with how the author derived his conclusion from his evidence?

If you look at PT45, S1, Q20, (C) fails on that second count. It doesn't even address the premise, the final idea after "for".

Hope this helps.