How to Weaken an Argument in GMAT Critical Reasoning

GMAT Critical Reasoning - image by Magoosh

More Than One Way

Often the strongest ways to attack an argument is to undermine one of its pivotal assumptions: that’s something I discussed in this post:

Arguments and Assumptions on-the GMAT.

Other ways of attacking an argument include:

a) questioning the evidence cited, and/or questioning the starting point

b) showing argument leads to an illogical or absurd further conclusion


Bad Evidence

In general, evidence is a good thing.  After all, good evidence is the basis of all authority in the natural & social sciences.  BUT, not all evidence is created equal.  Any scientist knows that while good evidence is worth its weight in gold, poor evidence—evidence that was not gathered by reliable means—is virtually worthless.

In an argument, evidence cited might be a study, but it also might be a particular authority figure or a generally held belief.  It’s hard to call a scientifically validated study into question, but many other kinds of starting points for arguments are not so solid.

For example, if my argument begins, “Professor Snodbuttons says that all stocks between $50 and $100 per share will increase by at least 20% between now and next January.  Therefore, etc.,” then one way to call the entire argument into question would be to question Prof. Snodbuttons’ credibility, or to point out that recently he was wrong on similar predictions.

If an argument begins with a general belief (“All professional athletes make a lot of money.  Therefore, etc.”), then it would weaken the argument to cite evidence to the contrary (e.g. “professional bowlers do not make a great deal of money.”)

A more subtle variant of these is: to affirm the evidence cited, but show that it is entirely independent of the argument.  For example, consider this argument:

     The vigorous stretching and environment of serenity created in a yoga class must have a positive effect on the heart.  Recent surveys have shown that long-term yoga practitioners have a lower incidence of heart disease than does the general population.

That argument wants to draw the conclusion: yoga is good for the heart.  It cites what seems as reasonably solid evidence: a study showing a negative correlation between yoga and heart disease.  It would be hard to attack the strength of the evidence as such, but consider this objection:

According to that same study, the vast majority of yoga participants are women, who suffer from heart disease at a much lower rate than men.

That’s a brilliant objection.  It doesn’t question the validity of the study at all.  Sure, yoga participants have lower rates of heart disease.  It just makes the study irrelevant to the conclusion: yoga participants have lower rates of heart disease, not because of the yoga, but because they are mostly women.  If the argument cites a piece of evidence, making that evidence irrelevant is a powerful objection.


Look Where It Goes!

Instead of focusing on the starting point, an attack on the argument can follow where the conclusion leads.  This can be a powerful way of attacking an argument without even getting into the specifics of the argument.

If the original conclusion of the argument implies further conclusions, some of which are unreasonable, illogical, or absurd, then this result simply shows something is wrong with the original conclusion.  It doesn’t matter how the argument arrived at that original conclusion—if it is implies something faulty, it’s a faulty conclusion.



In the Art of War, Sun-Tzu said: “Therefore, just as water retains no constant shape, so in warfare there are no constant conditions…He who can modify his tactics in relation to his opponent, and thereby succeed in winning, may be called a heaven-born captain.”  While we at Magoosh do not advocate open warfare :), Sun Tzu’s words have often found resonance in the business world, especially the financial market.  Here, they are quite pertinent to GMAT preparation.

In GMAT Critical Reasoning, when you are asked to weaken an argument, be flexible.  Keep in mind, there is more than one way to do this.  While undermining the assumption is usually the strongest attack, keep in mind the others we have discussed here.  If you can apply them all equal well in weakening arguments, perhaps we could call you “heaven-born” master of Critical Reasoning.


Here’s a practice CR question about element #70 on the Period Table:

Click to answer the question and view explanaiton


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  • Mike MᶜGarry

    Mike served as a GMAT Expert at Magoosh, helping create hundreds of lesson videos and practice questions to help guide GMAT students to success. He was also featured as "member of the month" for over two years at GMAT Club. Mike holds an A.B. in Physics (graduating magna cum laude) and an M.T.S. in Religions of the World, both from Harvard. Beyond standardized testing, Mike has over 20 years of both private and public high school teaching experience specializing in math and physics. In his free time, Mike likes smashing foosballs into orbit, and despite having no obvious cranial deficiency, he insists on rooting for the NY Mets. Learn more about the GMAT through Mike's Youtube video explanations and resources like What is a Good GMAT Score? and the GMAT Diagnostic Test.

12 Responses to How to Weaken an Argument in GMAT Critical Reasoning

  1. Panderichthys Rhombolepis December 5, 2017 at 12:03 am #

    Hi Mike!

    Your’s is a fab site!

    Just one thing (and I know I am being punctilious here; sorry!), but since Sentence Correction is one of the parts on the Verbal Section, I thought I should point out one of your sentences that needs, er, correction! 🙂

    On this page, under the section heading ‘Look where it goes’ is the rather odd sounding sentence: If the conclusion of the argument implies further conclusions, some of which are unreasonable, illogical, or absurd, then simply showing that shows something is wrong with the conclusion

    I am referring to the phrase: ‘showing that shows…” (an example of the use of a partially cognate object, perhaps?)

    The sentence would be less awkward if you were to replace one of the shows, perhaps with like this:

    If the conclusion of the argument implies further conclusions, some of which are unreasonable, illogical, or absurd, then simply illustrating the absurdness or illogicality would show the conclusion to be faulty.’

    I had to read this sentence several times over to make sense of it. Hence the (wholly unsolicited’ suggestion:

    Panderichthys Rhombolepis

    • Magoosh Test Prep Expert
      Magoosh Test Prep Expert December 7, 2017 at 11:02 am #

      Hi Panderichthys!

      I can see how that sentence may be hard to follow, and your suggestions is appreciated. I’ll touch base with Mike about possible revisions. Thanks so much for your suggestion! 🙂

  2. thang August 30, 2013 at 2:27 am #

    Thank you Mike
    in the question above:

    The vigorous stretching and environment of serenity created in a yoga class must have a positive effect on the heart. Recent surveys have shown that long-term yoga practitioners have a lower incidence of heart disease than does the general population.

    the following weakener

    According to that same study, the vast majority of yoga participants are women, who suffer from heart disease at a much lower rate than men.

    is in fact attacking an assumption.

    the evidence is correct: the participant in the yoga class are better than general population
    the assumption is that : the evidence is representative.
    the weakener is that : the evidence is not representative.

    so, you give us typical weakener: attacking an assumption.

    • Mike MᶜGarry
      Mike August 30, 2013 at 9:46 am #

      Dear thang,
      Here’s the thing — once you hear this objection, then yes, you usually can go back and frame things in a way that the correct answer is an objection that attacks an assumption that you tailor to match this objection. That often is possible, once you know the answer. BUT, when you encounter the argument prompt for the first time, it’s quite unlikely that most users would identify that as an assumption. There’s not necessarily a correlation between the ability to find the correct answer and the ability to reframe things with mental gymnastics after the fact.
      Does this make sense?
      Mike 🙂

  3. Andrew June 20, 2012 at 3:42 pm #

    Hi Mike,

    I agree that you cannot predict every assumption on GMAT CR weaken questions but the correct answer choice will be attacking an assumption of the argument. And attacking an assumption of an argument weakens that argument 100% of the time.


    • Mike MᶜGarry
      Mike June 20, 2012 at 4:44 pm #

      There are drawbacks to reducing any point to a tautology. In the practical matter of test prep, finding the assumption of an argument is a powerful *strategy* only insofar as it allows the student to predict the answer. If you expand the definition of assumption, and “attack on the assumption”, to include absolutely any new piece of information that strengthens or weakens the argument, then it’s true, tautologically you are always weakening the argument by attacking the assumption, but this view no longer leaves you with any strategy for dissecting the problem. Essentially, you are saying, , whatever the OA is to the “weaken the argument” question, no matter how novel or out-of-the-box or unpredictable, that by definition is an attack on the assumption — if you want to define it that way, great, you have a rule, but the rule is now so wildly large and without boundary that it is useless as a strategy. When a statement is true as a tautology, it no longer contains meaningful information.
      I suspect the larger issue is: you seem relatively talented at solving CR, and perhaps many GMAT CR problems seem relatively straightforward to you. It may well be, you don’t need any sophisticated strategies, because you are largely successful with these questions. That would certain explain why you wouldn’t find problematic a tautological definition that implied no additional strategy, because you are already successful in unlocking these arguments and don’t need much more help. Consider, though, that this blogpost is written more for folks who *do* need strategies, who *do* want help with the CR. For those readers, a tautological definition that implies no concrete strategies is astonishingly unhelpful. Do you see what I mean?
      Mike 🙂

  4. Andrew June 20, 2012 at 1:14 pm #


    I randomly came upon this post and I am not sure about the accuracy of this information. 4, 8, and, 20 are “flaw” questions so irrelevant. 25, 32, and 37 are weaken questions and you would weaken them by attacking the assumptions. You might have different ways of identifying what assumptions are being made. Maybe that is what you are discussing in this post? But you would have a difficult time weakening these arguments or any argument unless you were attacking the assumptions because there is nothing else to manipulate.

    Saying that attacking assumptions is formulaic is like saying that Pi * Radius Squared is formulaic.


    • Mike MᶜGarry
      Mike June 20, 2012 at 1:57 pm #

      First of all, in my mind, “find the flaw in the argument” and “weaken the argument” are two ways of saying virtually the same thing. Even if they are not strictly identical, there is enormous overlap between “flaw” questions and “weaken” questions. For #25, #32, and #37, it’s not necessarily clear to me that any of those “weaken” questions involve attacking the assumption. It seems to me in #25 and #32 and #37, that the OA’s involve introducing *new* information that changes the nature of the situation. In none of those three would you have been able to *predict* the correct answer before reading the answer choices: that’s precisely what you would be able to do if it were an “attack the assumption” question. GMAT CR is deeply contextual, and I will say, once again, the GMAT CR rewards flexibility and punishes a formulaic one-size-fits-all approach.
      Your analogy does not hold. Math uses formulae because A = (pi)*(r^2) yields the area of a circle in 100% of cases. A valid mathematical rule *is* a one-size-fits-all solution. That’s the nature of math. If you bring too much of that mathematical mindset to GMAT CR, you will not do well. The very virtue of math is a trap in CR.
      Does all this make sense?
      Mike 🙂

  5. duongthang May 1, 2012 at 1:07 am #

    I think that there is only one way of weakening the arguement, increasing doubt on an assumption. Other ways of weakening are in fact the same way of increasing doubt on an assumption. I see that in OG books , there is only one way of weakening. Pls, show me a problem in OG books, in which the weakening can be done other way. Thank you.

    • Mike MᶜGarry
      Mike May 1, 2012 at 11:54 am #

      Dear Duongthang,
      With all due respect, the OG CR problems are simply littered with questions that ask you to weaken the argument in ways other than attacking the assumption. For example, in the OG13e, pp. 500-538, see #4, #8, #20, #25, #32, #37, etc. Like everything else on the GMAT, CR questions reward flexible thinking and punish a purely formulaic approach. Does this make sense? Let me know if you have any further questions.
      Mike 🙂

  6. Ravi Sankar Vemuri April 28, 2012 at 2:22 am #

    The yoga one is a good example on “questioning the cited evidence” strategy.

    • Mike MᶜGarry
      Mike April 30, 2012 at 12:00 pm #

      Thank you. That approach, question the cited evidence, is a powerful “weaken the argument” option that folks often overlook. It’s great that you understand it.
      Mike 🙂

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