Q7 - If you know a lot

[mcrittell]

Def knew it was a formal logic question, and went straight to diagramming, but after I diagramming it, I had no idea what the flaw was. Ayudame por favor!

I have ~WVHLR-->~EII-->~AH-->~R#HB and its contrapositive R#HB-->AH-->EII-->WVHLR

Is it because when you flip it, you have another option, R#HB, before EII other than AH?

[timmydoeslsat]

It does have big time indicators of logical diagramming.

I like to write out the important words so I do not end up with crazy acronyms like ACBDJFJGJ!

You can view the stimulus like this:

Know a lot about history ---> Easy to impress intellectuals

~Read large # of books ---> ~ Know a lot about history

---------------------Therefore....

[~Read large # of books ---> ~ Know a lot about history] ---> ~Easy to impress intellectuals


This is an interesting stimulus in that it lends itself to diagramming quite well, yet a more abstract viewing of the stimulus will favor you more.

You see that "easy to impress intellectuals" is only mentioned in one of the premises before it is mentioned in the conclusion. The way in which "easy to impress intellectuals" is presented is as a necessary condition. The conclusion has the negation of this necessary condition. It not possible with these premises to get a negation of a necessary condition.

In other words, we know that if you know a lot about history, it will be easy for you to impress intellectuals. What else do we know that can easily impress intellectuals? Perhaps, current events? Perhaps knowing multitudes of languages? Perhaps being a physics genius?

Basically this stimulus is showing us that one way can easily impress intellectuals, and that if a certain condition is met (if you don't read large # of books) then that one way is no longer available. However, that does not mean that we cannot still easily impress intellectuals because you memorized 30 pages of the dictionary and can recite it backwards on demand.

[mcrittell]

Is my thinking wrong though?

[timmydoeslsat]

Your logic diagramming is hard for me to understand.

I do not see where you have your conclusion set apart from the premises.

You have one big chain and its contrapositive, however to see the flaw, you should see how the conclusion does not follow from the premises.

It basically did this

A ---> B

~ C ---> ~A

------------------>THEREFORE...

[~C--->~A] ---> ~ B

And we know that just because we do not have A, does not mean that we cannot have B. Sure, an avenue to B may have been eliminated, but there can be other avenues to B.

[ManhattanPrepLSAT1]

Let me just add something here... There are plenty of questions that ask you to identify the flaw and that are full of conditional logic. When that happens the correct answer will either say that

"the argument takes for granted that" the assumption is true.

or

"the argument fails to consider the possibility that" the assumption is not true.

We see two common forms on this one.

A --> B
~B --> ~C
-------------
A ---> C

In this case we need to figure out what the flaw is. If we change the second premise to B ---> C then the argument works. So the correct answer would either say that the argument

"takes for granted that all B's are C's."

or

"fails to consider that some B's are not C's."

In the second form

A ---> B
B ---> C
-----------
C ---> A

In this case the conditional that doesn't work is in the conclusion - not in the evidence. In this case the correct answer would say that the argument

"takes for granted that all C's are A's."

or

"fails to consider that some C's are not A's."

Notice that when the flaw is in the evidence we have to figure out what the argument "should have said" and when the flaw is in the conclusion we have to deal with what the argument did say.

Here are a few examples of this if you'd like some additional practice:

PT26, S3, Q17
PT25, S4, Q23

Good luck!

[cyt5015]

Seems to me that the second premise "/read -->/know much" does not affect the argument at all and we can totally remove that sentence. The argument will become:
know history-->easy to impress;
therefore, if not know history-->not easy to impress.
The correct answer will still be (D).
I think the second premise just makes the logic unnecessarily convoluted and tries to disguise the real flaw in the argument.
Is my understanding correct?
Thank you.

[ohthatpatrick]

Yeah, you're right. That's actually a point timmydoeslsat is making in his 1st post.

He said something to the effect of, "even though there are conditional triggers, a conceptual reading might be more helpful ... we're only told about something that WILL impress intellectuals. We're never told about anything that would NOT impress them."

So the 2nd sentence is definitely serving purely as filler. The flaw is completely based on the first sentence only being able to prove that you WILL impress, not that you WON'T impress.

It's a good reminder that we shouldn't rush into diagramming before having read the whole argument and allowed our conceptual brain to consider it first.

[A.june]

Hi All! Hope the studying is going well.

@matt I don't understand what you mean by "Notice that when the flaw is in the evidence we have to figure out what the argument "should have said" and when the flaw is in the conclusion we have to deal with what the argument did say." Aren't both conclusions flawed?

I saw the arugement as

KLAH -> EII (1st sentence)
~RAB -> ~KLAH (2nd sentence)
_________________
~RAB -> ~EII (3rd sentence)

The first premise was used incorrectly, is that a flaw in the evidence?

I saw the flaw but still took too long in finding and answering the question. How can I improve?

Is this just a lacking the sufficient doesn't mean you lack the necessary question?

Thank you.