Logical Reasoning

PT113 · S3 · Q21 Bank deposits are credited on the

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Bank deposits are credited on the date of the transaction only when they are made before 3 P.M. Alicia knows that the bank deposit was made before 3 P.M. So, Alicia knows that the bank deposit was credited on the date of the transaction.

Evidence

conditional (only when = only if = RIGHT side) Credited → made before 3pm A → B

fact Alicia knows made before 3pm. X knows B

Conclusion

Alicia knows credited. X knows A.

Evaluate

The question stem curious asks for both logical flaws, which is very atypical (only one or two others like this that have two flaws).

The more obvious flaw is the Necessary vs. Sufficient reversal. Famous Flaws are very common on Parallel Flaw questions.

The author provided a conditional relationship, but then misapplied it by thinking .

If we have no idea what the second flaw is, we can just head to the answers knowing this one and then see what we can rid of. Once you're down to the final couple, seeing the structural similarity that relates to the second flaw would probably be enough to make you pick the right answer.

The second flaw is something that's been used 5-10 times over LSATs history, so recurring but not too common. It's a flaw in which you assume that someone knows an implication of their belief.

You could say

WE know that he's driven through the birthplace of jazz. That is a true implication of the fact that he's driven through New Orleans. But just because Tony believes that he's driven through New Orleans doesn't mean he believes every true implication of that fact. He might have no idea that New Orleans is the birthplace of jazz.

Similarly, Alicia knows she made her deposit before 3pm. WE know that there's a rule saying "credited same day requires before 3pm", so we know that her deposit qualifies for being credited same-day, but we can't say that SHE knows that her deposit qualifies for being credited same-day, because we have no idea if she's aware of this bank's policy. She might have just dropped the deposit off in the morning because it was on her way to yoga, and so she knows it was before 3pm but doesn't have any reason to think 3pm is a special deposit cutoff time for her bank.

Goal

Look for a conditional statement that the argument then interprets backwards (if right side is true, left side is true). Then look to see whether those last two moves are about someone's beliefs (since X believes right side, X believes left side).

21.

Which one of the following exhibits both of the logical flaws exhibited by the argument above?

  1. Journalists are the only ones

    Misses 2nd Flaw

    This has the illegal reversal ("the only" is a sufficient indicator, unlike the much more common "only / only if" which are necessary indicators). But it doesn't have a person's thoughts taking us from right side to left side. P1: A ? B Q ? J P2: X knows B. X is a J. C: X knows A. X is a Q.

    13% picked this

  2. We know that Patrice works

    Misses 2nd Flaw

    This has the illegal reversal ("only / only if" are necessary indicators). But it doesn't have a person's thoughts taking us from right side to left side. It just has "we know" around the conditional (also, the flaw won't really be a flaw if we put a we know on all these ideas. It's only a flaw when we're talking about someone else and we're not sure that they know all the relevant information you'd need to derive the implication we accuse them of). P1: A ? B We know "W ? Th" P2: X knows B. Today is Th. C: X knows A. Today is W.

    22% picked this

  3. Correct

    It is clear that George

    Why this is right

    This has the illegal reversal ("only / only if" are necessary indicators). And it has the second flaw where we go from right side to left side acting like "If someone has This belief, they have That belief". P1: A ? B SS ? HR P2: X knows B. G knows HR. C: X knows A. G knows SS.

    Skill tested: Parallel Flaw · how this choice captures the argument's function is the move to repeat next time.

    60% picked this

  4. John believes that 4 is

    Misses 1st Flaw

    This has the illegal "implication of belief" flaw, but not the illegal Necessary vs. Sufficient reversal. There's no conditional logic for it to mess up. P1: A ? B J knows X is A. P2: X knows B. J knows X is B. C: X knows A. J knows "some A are B"

    2% picked this

  5. Pat wants to become a

    Misses First Flaw

    This definitely doesn't have any reversal. I don't even really want to call "it's well known that social workers are poorly paid" a conditional, but we could certainly construe it as Social Worker ? Poorly Paid Even so, the argument doesn't go from poorly paid to social worker. It says "Pat wants social worker", so "Pat wants poorly paid". This is fairly close to being the 2nd flaw, although this is less about assuming an implication of someone's belief, and more about "Just because they want X doesn't mean they want every causal ramification of X." Given that there's no conditional logic reversal, though, we don't need to think hard about that.

    4% picked this

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