An Ancient Technique for Cracking GMAT Critical Reasoning Questions

One of the key things to remember in the GMAT’s critical reasoning section is that the argument is designed to have a flaw. You just need to figure out what that flaw is.

• The flaw itself is an invalid assumption, which will almost invariably go unstated.

The easiest way to do this is through a method commonly attributed to the work of Aristotle, some 2,300 years ago.

• The method is called ‘reduction to absurdity’ [also known as ‘reductio ad absurdum’].

In short, reduction to absurdity relates to proving that an ‘absurd’ circumstance is possible within the confines of the argument.

After all, that’s the purpose of this type of argument on the GMAT. You’re presented with a series of facts, then a generalization based on those facts. In the case that this generalization is not ‘reasonably true’ or does not ‘directly follow’ from the facts, then boom – you have a flaw.

In short, you’re trying to drive a wedge between the facts and the conclusion by proving that the facts can somehow be true while the conclusion itself is false.

How to tell when a critical reasoning argument doesn’t follow

It’s very simple to tell when a conclusion doesn’t directly follow from its stated facts. You may have already guessed it from the previous statement.

• Simply assume the facts to be true and the conclusion to be false, and ask yourself how this might be possible.

Want to systematize it?

1)      Catalogue the facts; what is presented as an objective statement – is it something that you could measure, write down, or take a photograph of?

2)      Identify the conclusion; what is presented as an opinion statement – is it something that involves someone’s judgment? (Hint: Look for words such as ‘clearly’ or ‘must’)

3)      Assume the facts to be true and incontrovertible.

4)      Ask yourself; “how is it possible that the conclusion is not true?”

Think of any circumstance, no matter how unlikely, that would allow this. In many cases, the more unlikely the better.

Nevertheless, what’s confusing about the GMAT’s critical reasoning arguments is that many of the arguments aren’t terrible – they might well be true in many cases!

Remember, though, you’re looking for what is necessarily true. Or, ‘always true’. That is very different from ‘possibly true’, or, “yeah, maybe, sometimes true.”

What you’re looking for is the exception – the weird little circumstance – where the conclusion can be false. It follows, then, that the invalid assumption will be some sort of little ‘fudge factor’ that’s used to gloss over this outlying little problem.

In other words, the argument tries to say, “Ah, well, we can just ignore that little detail, right?” Wait. Not so fast. We’ve just caught them out.

Apply the reduction to absurdity method early and often

Unless a GMAT question specifically asks you to draw a conclusion based on provided facts, there will be a flaw in its critical reasoning argument.

Let’s try it on a tricky argument:

When analyzing the body armor of its returning combat troops, Bactrian Army officials recently discovered that the armor was most frequently damaged in the arms, legs, and lower torso. Therefore, in order to decrease serious injury among its deployed combat troops most effectively, the Bactrian Army has decided to increase the strength of its arm, leg, and lower torso armor.

Makes pretty decent sense, right? Facts-wise, we’re looking at a group of people who have been on the front lines, and it seems that the armor is being damaged in specific places. Conclusion-wise, we see that, to lower rates of serious injury ‘most effectively’ for all deployed troops, the Bactrian Army has decided to armor those specific places more heavily.

Now, let’s apply the reduction to absurdity method to see whether we can see drive a wedge into this argument, and if so, where. 

Reduction to absurdity: How is it possible that we would not lower rates of serious injury 'most effectively' by armoring the arms, legs, and torso?

That is, is there any reason this wouldn’t be the most effective way to decrease the rates of serious injury? Notice how I’m leaning on the words ‘most effectively’ here. That extreme superlative is exactly where we can drive our wedge in.

In short, could something else be more effective? Perhaps, but we need to revisit the facts to see exactly how. Who are we talking about? Notice that our sample is the returning combat troops, not all deployed troops, as the conclusion suggests.

So, what would the difference here be? Is there some difference between the ‘returning combat troops’ and the ‘deployed combat troops?’ Yes – some of them don’t return, and we’re only looking at the ones who do.

Is there a possible difference there? Yes; what about those who don’t return? Why don’t they return? Perhaps it is because they are injured in a place that goes conspicuously unmentioned – the upper torso.

If upper torso injuries mean that the soldiers don’t return at all, there is a good argument that increasing the armor for the upper torso would be an effective way to reduce ‘serious injury’ among deployed troops.

Note that this doesn’t mean the argument is absolutely wrong, but it doesn’t necessarily have to be correct. That’s all we’re looking for here.

What did we do?

1)      We suggested the negation of the conclusion.

2)      We revisited the facts and the extreme language of the conclusion (‘most effectively’).

3)      We determined that the negation of the conclusion is possible, thereby proving that the argument is not necessarily (always) true.

Nevertheless, as this is a tricky question, its flaw may not be immediately obvious. That’s because we simply assume that the returning soldiers are the same class as the deployed soldiers, but that’s not necessarily a great idea.

By negating the conclusion, we can immediately highlight the assumption: That while the proposed solution may be effective, it is not necessarily the ‘most effective’ solution. Note how extreme language made the argument spring a leak.

Thank Aristotle

Next time you’re stuck, just remember the absurd (and give old Aristotle a tip of the hat). If the conclusion and its negation are both possible, this critical reasoning argument isn’t going to fly.