PT 14 Sec 4 Q9 - Formal Logic

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jocelyne

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Joined: Tue Nov 11, 2008 4:15 am

PT 14 Sec 4 Q9 - Formal Logic

I couldn't diagram this. Would anyone be able to help me out?

goansongo

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Joined: Thu Apr 03, 2008 6:19 am

Re: PT 14 Sec 4 Q9 - Formal Logic

Premise 1: Elected--->~Support New Tax Plan
Premise 2: Support New Tax Plan--->~Understand Econ
Therefore: Elected -------->Understand Econ

Assumes: ~Support New Tax Plan---> Understand Econ (which is a reversal of premise 2) when this can be the case ~Support New Tax-->~Understand Econ.

joonhp

Posts: 157
Joined: Sat Feb 27, 2010 5:19 pm

Re: PT 14 Sec 4 Q9 - Formal Logic

Will someone explain this to me? I get the diagram...I am not making the connection to the answer.

skip james

Posts: 262
Joined: Sat Sep 19, 2009 2:53 am

Re: PT 14 Sec 4 Q9 - Formal Logic

Well.. since no one has attempted this one, I'll give it a shot. =)

I actually love this problem, since I came to realize a while back that this is, in fact, what makes flawed questions as hard as they are. The trick to this question (and lots more like this one), is in the how the flaw is being described...

Or... in other words, the key is knowing what the difference between stems entails of the answer of the correct answer choice. So let's just take these two common flaw stems and take a look at the difference:

the argument is flawed because the author...

1) ... assumes that...
... presumes, without justification, that...
... takes for granted that...

from 2) ...ignores the possibility that...
...neglects the possibility that...
...overlooks the fact that...

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A Closer Look at (1)
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If we look at stem type (1), the verb indicates something the author needs to make his argument succeed. In other words, the clause that follows the 'that' will be an implicit assumption that the author makes in his argument and, from my experience, this assumption is generally be sufficient to make the argument logically valid.

The implications of this is fricking mind-boggling to me. This essentially means that when prompt starts with 'assumes that...', you should be able to prephrase an answer by treating the argument like a sufficient assumption.

So take this argument as an example:

All lions are furry.
Thus, all lions can make great coats.

If I treat this like a sufficient assumption, then I look for the assumption that logically validates this argument, i.e. 'All furry things can make great coats'.

Thus, for a flaw question, if the answer choice starts with 'the argument is flawed because the author assumes...', I would be able to prephrase what should follow if it was correct. Or:

'the argument is flawed because the author takes presumes, without warrant, that all furry things make great coats'

But the answer would look different under a flaw type 2 stem! so what does stem (2) entail? and why?

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A Closer Look at Stem Type (2)
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Looking at stem type 2, we can see that the verb describing what the author is doing is a negative one, i.e. 'the author is overlooking' or 'the author is ignoring'. When I say 'negative' I mean that these descriptors describe something that the author is NOT considering or doing (which he should be doing), or perhaps is assuming something in a logically bad way.

To get at the core of the matter, whatever assumption that the author is making is a logically bad assumption because it DOES NOT have to be true. Since LSATers are supposed to take all premises as being true (even if they aren't in real life), the only things we can doubt as being true are these unstated premises, i.e. assumptions. So, since the author's assumption is an unstated premise, we are allowed to consider - and should consider - the possibility that the author's assumption is NOT true.

So when given something like this: 'the author ignores the fact that X', the clause X is exactly that, i.e. the possibility that his assumption IS NOT TRUE. Again, the clause X is basically the statement, 'it is not true that [author's assumption]'.

But saying 'it's not true that Blah blah' is TO NEGATE 'Blah blah'! So here we have one of the real reasons (there are others but that's unimportant right now) why flaw answer choices can be so hard to interpret!

BECAUSE you're forced to read statements and understand the negated versions of them in the answer choices! LSAC thus basically forces you to flipflop with an assumption and its negated version whenever they alternate answer choices with 'assumes' then 'overlooks' then 'presumes' then 'ignores'... (fricking bastards...)

So returning to my hypothetical argument:

All lions are furry.
Thus, all lions can make great coats.

Since the author assumes that 'all furry things make great coats', if we negate this assumption we can stick it onto Flaw Type 2 stems and have ourselves a correct answer! The negation would be 'some furry things do not make great coats'

So this could also be a correct answer:

'the argument is flawed because the author fails to consider that some furry things do not make great coats'.

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So returning to the problem from PT 14 Sec 4, Q9...

We've established that (1) the author is making a conditional error (mistakenly negating both sides of a conditional) and that (2) he is thus assuming that 'all those do NOT support the new tax plan must understand economics'.

So under a Flaw Type 1 Stem the correct answer choice for this question could look like this:

"The argument is flawed because the author assumes, without warrant, that all those do NOT support the new tax plan must understand economics'

But under a Flaw Type 2 Stem, the correct answer choice would look like this:

"The argument is flawed because the author ignores the possibility that his assumption that [all those do NOT support the new tax plan must understand economics] is NOT TRUE' or...

"The argument is flawed because the author ignores the possibility that some people who do NOT support the new tax plan do NOT understand economics'

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Caveat: These are not the only types of flawed answer choices that exist. There are more variants (things I have some cheesy nicknames for, but whatever), so don't think that this is all there is to flawed answer choices. Just the tip of the iceberg.

Also, you should realize that there are some super tricky ways for LSAC to really screw you up with this too! They could start an answer choice with 'the author assumes... and the NEGATE the assumption' and they could start an answer choice with 'the author ignores... and then just GIVE you the assumption'. Both would be incorrect! If you want to see an example of this super brutal trick, check out June 2007 (the free test on LSAC), Section 3, question 18, answer choice C. Frickin brutal...

But this just goes to show how important it is to be on top of negations, not just your ability to use it on necessary assumption questions, but to be able to SPOT and understand them in flawed answer choices.

joonhp

Posts: 157
Joined: Sat Feb 27, 2010 5:19 pm

Re: PT 14 Sec 4 Q9 - Formal Logic

Thanks alot. This really helps.

skip james

Posts: 262
Joined: Sat Sep 19, 2009 2:53 am

Re: PT 14 Sec 4 Q9 - Formal Logic

joonhp wrote:Thanks alot. This really helps.
glad you got something out of it.