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Flawed Argument Untrue-Valid Argument.

by dddanny2006 » Thu Feb 20, 2014 7:13 am
Hey guys,
I need help in understanding some of these concepts.

I dont seem to understand why this argument is said to be weak:

"The Jacksonville area has just over one million residents.Cincinnati has almost two million residents.The New York area has almost twenty million residents.Therefore,we should move to Jacksonville."

We clearly can figure out that the person wants to move to a low population zone,among the 3 choices that are given in the argument.How can we classify this as a weak argument?

Here's a strong argument:

"The trees that shed their foliage annually are deciduous trees.Black Oak trees shed their leaves every year.Therefore,Black Oak trees are deciduous."

If one can argue about the previous argument being weak,then we can certainly argue about this one too.Why are we talking only about Black Oak trees?or there may be other factors like- some trees only shed their leaves,while the others don't.

Please explain about identifying strong and weak arguments.

I have one more question to ask-

"All birds can fly.An ostrich is a bird.Therefore it can fly." ----------1

This is an example for an argument that is valid without being true.Now what do we make of such an argument?We're supposed to accept any GMAT premise without checking them in reality.So,what if someone who didn't know the Ostrich's fly-ability,and got this question on the GMAT?

Consider the following example
"My mail was delivered yesterday,so it will also be delivered today".------------2

The book I'm referring to calls this a flawed argument,how can we be so sure?Yes,today could be a Sunday too,but we're not sure.If the GMAT tells us to accept whatever premise we get as the absolute truth,how do we disprove it?

Please tell me the difference between a Untrue-Valid argument as in 1,and the so called Flawed argument as in 2.
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by Patrick_GMATFix » Thu Feb 20, 2014 11:20 am
Hey Daniel,

A flawed argument is one that makes significant assumptions. The more numerous and the more farfetched the assumptions, the more flawed the argument. Another way to look at it: An argument is flawed if its premises alone are not sufficient to prove its conclusion.
"The Jacksonville area has just over one million residents.Cincinnati has almost two million residents.The New York area has almost twenty million residents.Therefore,we should move to Jacksonville."
We clearly can figure out that the person wants to move to a low population zone,among the 3 choices that are given in the argument.How can we classify this as a weak argument?
The argument is weak because we do not know that moving to Jacksonville would accomplish the author's objective. If as you wrote, the author wants to move to a low population zone, Jacksonville is indeed the best of the three options. Problem is, from the argument we have no idea what the author is trying to achieve: low population? low crime? good schools? low taxes? Without that info, we don't know whether the conclusion that "we should move to Jacksonville" is strong.
"The trees that shed their foliage annually are deciduous trees.Black Oak trees shed their leaves every year.Therefore,Black Oak trees are deciduous."
Why are we talking only about Black Oak trees?or there may be other factors like- some trees only shed their leaves,while the others don't.
This argument is as strong as they get. There is no assumption made. It's equivalent to "businesses that earn more than they spend are profitable. Businesses of Type A spends more than it spends, therefore, Businesses of Type A are profitable" The fact that some businesses do not earn more than they spend has no impact on this argument because the conclusion limits itself to businesses that do earn more. Likewise, trees that do not shed their leaves are irrelevant to your argument because the conclusion is limited to trees that do shed their leaves. To make the case that the argument is weak, you would need to identify an assumption.
"All birds can fly.An ostrich is a bird.Therefore it can fly."
This is an example for an argument that is valid without being true.Now what do we make of such an argument?
The Ostrich argument above would not appear on the GMAT (as you pointed out, some birds cannot fly) but a similarly structured argument "All Xs can fly. Y is an X, so Y can fly" would be a strong argument. There are two types of premises: data premises and reasoning premises.
Data premises: In most case, you should accept these as fact. One exception: if the method used to gather the data is part of the argument (ex: a sample study), you could challenge the fairness or accuracy of the method. For instance, we can ask whether sampling results will be replicated in the general population.
Reasoning premises: These are opinions (not data) used to support the conclusion. Because they are not the conclusion, they are premises. Like any opinion, they can be challenged if they make assumptions.

"A study of 50 teens showed that teens who eat breakfast are more likely to excel in school. Since eating breakfast helps teens excel, we should serve breakfast in schools to improve average academic performance." The green text is data premise. We cannot challenge the existence of the study, but we can challenge how relevant its findings are (Are these 50 teens representative of all the students who will be affected?). The blue text is reasoning premise; it is the author's opinion rather than a fact, so it can be challenged (correlation of breakfast and good grades may not mean that breakfast is the reason for good grades)
"My mail was delivered yesterday,so it will also be delivered today".
The book I'm referring to calls this a flawed argument,how can we be so sure?Yes,today could be a Sunday too,but we're not sure
Do not confuse "a flawed argument" with "a wrong argument". Remember that an argument is flawed if it makes an assumption. You're right, we're not sure about what will happen today. The mail may indeed be delivered. However the fact that we're not sure means that the argument makes an assumption about what yesterday tells us about today; because the argument makes an assumption, it has a weakness (it is flawed).
If the GMAT tells us to accept whatever premise we get as the absolute truth,how do we disprove it?
Most of the time, with the exception about methods for gathering data I alluded to earlier, we should indeed accept data premises as truth. What we are asked to disprove/weaken is usually not the data premise, but the conclusion (or sometimes the reasoning premise). The conclusion is an opinion that the author justifies/supports using the premise. In a flawed argument, the premises alone do not prove that the conclusion is correct; the conclusion also relies on assumptions. Therefore, to disprove/weaken an argument we usually challenge its assumptions or introduce counter premises; no need to disprove data premises themselves (again, with the exception I mentioned above).

On a final note, be careful not to equate "weaken an argument" with "disprove an argument". When a question asks you to weaken an argument, the right answer does not actually need to disprove it, but only to make its conclusion less convincing; this is a much lower bar to clear.

Hope this helps,
-Patrick
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by dddanny2006 » Thu Feb 20, 2014 11:41 am
Thanks a lot for your response Patrick.I have a few doubts though.

The argument is weak because we do not know that moving to Jacksonville would accomplish the author's objective. If as you wrote, the author wants to move to a low population zone, Jacksonville is indeed the best of the three options. Problem is, from the argument we have no idea what the author is trying to achieve: low population? low crime? good schools? low taxes? Without that info, we don't know whether the conclusion that "we should move to Jacksonville" is strong.
Isn't low population enough for us to understand about the strength of this argument?People prefer staying in low populated cities right-less pollution,less traffic,a laid back life. etc

Next,
Can you please explain a bit more about Data premise,Reasoning premise?How do we identify Reasoning premises from other premises,let alone data premises.By data-do you only mean numbers.Also we're told that Premises should be accepted as the truth and thus remain unchallenged,how do we challenge the reasoning premises and data sampling premises if thats the case?"All Xs can fly. Y is an X,,what kind of a premise is this?Is it a data premise or is it a Reasoning premise?Also what premise is "My mail was delivered yesterday,so it will also be delivered today"-the bolded area.Please tell me more about identifying data premises and reasoning premises.
The Ostrich argument above would not appear on the GMAT (as you pointed out, some birds cannot fly) but a similarly structured argument "All Xs can fly. Y is an X, so Y can fly" would be a strong argument. There are two types of premises: data premises and reasoning premises.
Data premises: In most case, you should accept these as fact. One exception: if the method used to gather the data is part of the argument (ex: a sample study), you could challenge the fairness or accuracy of the method. For instance, we can ask whether sampling results will be replicated in the general population.
Reasoning premises: These are opinions (not data) used to support the conclusion. Because they are not the conclusion, they are premises. Like any opinion, they can be challenged if they make assumptions.

"A study of 50 teens showed that teens who eat breakfast are more likely to excel in school. Since eating breakfast helps teens excel, we should serve breakfast in schools to improve average academic performance." The green text is data premise. We cannot challenge the existence of the study, but we can challenge how relevant its findings are (Are these 50 teens representative of all the students who will be affected?). The blue text is reasoning premise; it is the author's opinion rather than a fact, so it can be challenged (correlation of breakfast and good grades may not mean that breakfast is the reason for good grades)
If Data premises(with exception of Poll studies),and reason premises can be challenged or questioned,how can we simultaneously accept them as truth?I find that a little contradictory to whats below here.
Most of the time, with the exception about methods for gathering data I alluded to earlier, we should indeed accept data premises as truth. What we are asked to disprove/weaken is usually not the data premise, but the conclusion (or sometimes the reasoning premise). The conclusion is an opinion that the author justifies/supports using the premise. In a flawed argument, the premises alone do not prove that the conclusion is correct; the conclusion also relies on assumptions. Therefore, to disprove/weaken an argument we usually challenge its assumptions or introduce counter premises; no need to disprove data premises themselves (again, with the exception I mentioned above)
Thank you Patrick
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by Patrick_GMATFix » Thu Feb 20, 2014 2:35 pm
Isn't low population enough for us to understand about the strength of this argument?People prefer staying in low populated cities right-less pollution,less traffic,a laid back life. etc
Not everyone prefers small cities; large cities have their own advantages (more employers, more opportunities for employment and fun activities, closer to major airports, etc...). The argument is flawed because it makes a big assumption about smaller cities. Anyway, we still don't know what the author is trying to accomplish, so we don't have enough info to conclude that moving to Jacksonville is the right thing to do.
Can you please explain a bit more about Data premise,Reasoning premise?How do we identify Reasoning premises from other premises,let alone data premises.By data-do you only mean numbers
Most arguments have two parts: premises and a conclusion. The conclusion is the ultimate opinion, what the rest of the argument tries to justify. All other points are premises. The difference between a data premise and a reasoning premise is simple: a data premise is presented as a fact (not just numbers): "All Xs can fly" and "My mail was delivered yesterday" are data premises. On the other hand, a reasoning premise is an opinion.
If Data premises(with exception of Poll studies),and reason premises can be challenged or questioned,how can we simultaneously accept them as truth?I find that a little contradictory to whats below here.
You misunderstood me. Data premises (facts) should not be challenged. Reasoning premises (opinions) can be challenged if they make their own assumptions.

"A study of 50 teens showed that teens who eat breakfast are more likely to excel in school. Since eating breakfast helps teens excel, we should serve breakfast in schools to improve average academic performance."

In this example, we cannot challenge the facts (data premises) that there was a study of 50 teens and that teens in that study who eat breakfast are more likely to excel. We can challenge the opinion (reasoning premise) that eating breakfast helps teens excel, and the opinion (conclusion) that we should serve breakfast in schools to improve grades.
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by dddanny2006 » Fri Feb 21, 2014 10:31 am
Thanks for that Patrick.I understood your point.How can we differentiate between a reasoning premise and a conclusion?Is the last sentence of the attached image a Reasoning premise?
Thanks again,
Dan
Patrick_GMATFix wrote:
Isn't low population enough for us to understand about the strength of this argument?People prefer staying in low populated cities right-less pollution,less traffic,a laid back life. etc
Not everyone prefers small cities; large cities have their own advantages (more employers, more opportunities for employment and fun activities, closer to major airports, etc...). The argument is flawed because it makes a big assumption about smaller cities. Anyway, we still don't know what the author is trying to accomplish, so we don't have enough info to conclude that moving to Jacksonville is the right thing to do.
Can you please explain a bit more about Data premise,Reasoning premise?How do we identify Reasoning premises from other premises,let alone data premises.By data-do you only mean numbers
Most arguments have two parts: premises and a conclusion. The conclusion is the ultimate opinion, what the rest of the argument tries to justify. All other points are premises. The difference between a data premise and a reasoning premise is simple: a data premise is presented as a fact (not just numbers): "All Xs can fly" and "My mail was delivered yesterday" are data premises. On the other hand, a reasoning premise is an opinion.
If Data premises(with exception of Poll studies),and reason premises can be challenged or questioned,how can we simultaneously accept them as truth?I find that a little contradictory to whats below here.
You misunderstood me. Data premises (facts) should not be challenged. Reasoning premises (opinions) can be challenged if they make their own assumptions.

"A study of 50 teens showed that teens who eat breakfast are more likely to excel in school. Since eating breakfast helps teens excel, we should serve breakfast in schools to improve average academic performance."

In this example, we cannot challenge the facts (data premises) that there was a study of 50 teens and that teens in that study who eat breakfast are more likely to excel. We can challenge the opinion (reasoning premise) that eating breakfast helps teens excel, and the opinion (conclusion) that we should serve breakfast in schools to improve grades.
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by Patrick_GMATFix » Fri Feb 21, 2014 12:21 pm
Daniel,

The argument you attached contains two opinions; the teachers' and the author's. The last sentence is the author's conclusion.

All arguments (except some Resolve the Paradox and all Inference/Draw a Conclusion) contain a conclusion. Not all arguments contain a reasoning premise. For arguments that contain both a reasoning premise and a conclusion, you can distinguish between the two by asking yourself which is the supporting logic and which is the ultimate point? The conclusion is the ultimate point; the reasoning premise is the supporting logic.

Again, consider my argument: "A study of 50 teens showed that teens who eat breakfast are more likely to excel in school. Since eating breakfast helps teens excel, we should serve breakfast in schools to improve average academic performance."

here there are two opinions, so how do we distinguish the conclusion from the reasoning premise? I find out which is the supporting logic and which is the ultimate point by asking myself which makes sense:

1: Eating breakfast helps teens excel, therefore we should serve breakfast to improve grades
OR
2: We should serve breakfast to improve grades, therefore eating breakfast helps teens excel

The correct structure of an argument is:
__[premise]____, therefore _[conclusion]___

Since the 1st option above makes most sense, the blue text is the reasoning premise and the dark red is the conclusion

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by dddanny2006 » Fri Feb 21, 2014 12:27 pm
Ok.So in the attached argument,since there is no Reasoning premise to challenge,we directly challenge the Conclusion,right?
Also,is it always the case that a reasoning premise is preceded by a Premise indicator?
Patrick_GMATFix wrote:Daniel,

The argument you attached contains two opinions; the teachers' and the author's. The last sentence is the author's conclusion.

All arguments (except some Resolve the Paradox and all Inference/Draw a Conclusion) contain a conclusion. Not all arguments contain a reasoning premise. For arguments that contain both a reasoning premise and a conclusion, you can distinguish between the two by asking yourself which is the supporting logic and which is the ultimate point? The conclusion is the ultimate point; the reasoning premise is the supporting logic.

Again, consider my argument: "A study of 50 teens showed that teens who eat breakfast are more likely to excel in school. Since eating breakfast helps teens excel, we should serve breakfast in schools to improve average academic performance."

here there are two opinions, so how do we distinguish the conclusion from the reasoning premise? I find out which is the supporting logic and which is the ultimate point by asking myself which makes sense:

1: Eating breakfast helps teens excel, therefore we should serve breakfast to improve grades
OR
2: We should serve breakfast to improve grades, therefore eating breakfast helps teens excel

The correct structure of an argument is:
__[premise]____, therefore _[conclusion]___

Since the 1st option above makes most sense, the blue text is the reasoning premise and the dark red is the conclusion

-Patrick
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by Patrick_GMATFix » Fri Feb 21, 2014 12:35 pm
Ok.So in the attached argument,since there is no Reasoning premise to challenge,we directly challenge the Conclusion,right?
Depends on the question. If you're asked what would weaken the argument, then yes the right answer would challenge the conclusion by either introducing a premise that disagree with the author's conclusion or by challenging the author's assumptions.
Also,is it always the case that a reasoning premise is preceded by a Premise indicator?
I don't know; I don't look for such indicators personally. I know that if I read an opinion, either it's the conclusion or it's a reasoning premise. If the argument has multiple opinions and I have trouble identifying the conclusion, I then use the technique from my earlier post.
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by dddanny2006 » Fri Feb 21, 2014 12:56 pm
Thank you so much Patrick.Your technique is very effective.I have 60days left for my GMAT,and I'm yet to finish SC,CR and RC.I'm done with Number properties,Algebra,WordProblems.Geometry and Fractons,decimals,and percentages are yet to be done.Do you think I'm in a bad position,with very limited time left?Can I get a 700+ within this time frame?How long do average students take to get that 700+ number?Is it possible in 2months?I'm jobless by the way,I can dedicate hours,how many should I dedicate in a day to get that 700+ score?Your advice is really appreciated.Thanks.
Patrick_GMATFix wrote:
Ok.So in the attached argument,since there is no Reasoning premise to challenge,we directly challenge the Conclusion,right?
Depends on the question. If you're asked what would weaken the argument, then yes the right answer would challenge the conclusion by either introducing a premise that disagree with the author's conclusion or by challenging the author's assumptions.
Also,is it always the case that a reasoning premise is preceded by a Premise indicator?
I don't know; I don't look for such indicators personally. I know that if I read an opinion, either it's the conclusion or it's a reasoning premise. If the argument has multiple opinions and I have trouble identifying the conclusion, I then use the technique from my earlier post.
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by Patrick_GMATFix » Fri Feb 21, 2014 8:26 pm
Hey Daniel,

I'm glad my posts help. Without working with you through the material to see what your weaknesses and learning abilities are, any specific feedback would only be speculative. Different people have different needs for time it takes to prepare and optimal ability once they are done prepping.

That said, I can say that generally speaking it takes me about 2.5 to 3 months working about 20 hours a week to thoroughly work through all the material with my clients. Of course it takes a lot less time for people who need to work on limited areas only. In short, you want to score above your target score in practice before you go in for the real test because in my experience most people see their scores drop from practice to real test.

Number of hours per week and number of weeks alone are not a good indicator of solid prep program however. If the time is used poorly, or is spent working with mediocre sources, it may still not lead to optimal results. You are welcome to read through the Self-Study Guide I've posted on my site to get an idea of how I would prepare. From the GMATFix homepage, click "Resources" -> "Documents & Links" in the menu bar. The top left result will be the Self-Study guide

Good luck,
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by dddanny2006 » Mon Feb 24, 2014 4:09 am
Thank you Patrick..GMAT fix is awesome.I will spread the word.
Patrick_GMATFix wrote:Hey Daniel,

I'm glad my posts help. Without working with you through the material to see what your weaknesses and learning abilities are, any specific feedback would only be speculative. Different people have different needs for time it takes to prepare and optimal ability once they are done prepping.

That said, I can say that generally speaking it takes me about 2.5 to 3 months working about 20 hours a week to thoroughly work through all the material with my clients. Of course it takes a lot less time for people who need to work on limited areas only. In short, you want to score above your target score in practice before you go in for the real test because in my experience most people see their scores drop from practice to real test.

Number of hours per week and number of weeks alone are not a good indicator of solid prep program however. If the time is used poorly, or is spent working with mediocre sources, it may still not lead to optimal results. You are welcome to read through the Self-Study Guide I've posted on my site to get an idea of how I would prepare. From the GMATFix homepage, click "Resources" -> "Documents & Links" in the menu bar. The top left result will be the Self-Study guide

Good luck,
-Patrick
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