Do You Make the #1 Conceptual Error in GMAT Logic?

How does the GMAT like to trick testtakers?

Well, if I could answer that with one statement, I would be a very rich man. Rest assured, I’m working on it!

Nevertheless, we can come pretty damn close to figuring out what the GMAT testwriters want from us.

This applies to all the five primary sections of the GMAT, both Quant and Verbal: Problem Solving, Data Sufficiency, Critical Reasoning, Reading Comprehension, and to a minor degree, Sentence Correction.

The idea is the distinction between Deductive Logic and Inductive Logic.

Deductive Logic is a sort of “top-down” logic that tells us that the conclucion of the argument is actually fully contained within the premises.

Aside: what are premises? Well for GMAT prep purposes, that means anything, fact or assumption, that is not the conclusion of the argument.

So in Deductive Logic, if the premises of an argument are true, then the conclusion must be true.

Before you get too concerned about memorizing definitions, just think of this simple example:

–In a Problem Solving problem any equation where we have to “solve for x,” for example, will be a deductive situation.

In essence, we are simply rearranging what is already there. Thus, the information we want is coded inside the premises.

It might not be easily accessible, but it is most certainly there if you shake hard enough.

–In a Reading Comprehension problem, the question asks “Which of the following is true?”

Only one of the answer choices will give information that is accurate with respect to the text.

Thus the text itself holds the information. No other effort is required, aside from perhaps a simple paraphrase of the basic facts listed.

You can think of Deductive Logic as simply rearranging facts. Or rearranging deck chairs on a sinking ship, if you prefer.

Nevertheless, Deductive Logic cannot have true premises and a false conclusion. If your premises are solid, you can pass Go and collect your $200.

There’s a pretty solid reason that the GMAT avoids fact-based questions like the plague.

This is tremendously unfortunate, as entire books are written about fallacies in Deductive Logic.

Still… perhaps one in eight Reading Comprehension questions are Deductive, and shockingly few Critical Reasoning questions are deductive.

Can you guess why that is?

Maybe they are too ingrained in our thinking.

Think about the most obvious feature of Deductive Logic. The true premises yield a true conclusion.

However, classical rhetorical arguments—the arguments used so deftly by politicians, businesspeople, salespeople, etc.—tend to be inductive.

What happens when you have true premises but ALLOW THE CONCLUSION TO BE FALSE?

This is the key to GMAT logic. It will unlock Data Sufficiency and Critical Reasoning, and provide a foolproof check on your Reading Comprehension.

Wouldn’t you like to know? Enter the rabbit hole of Inductive Logic. We have a lot to talk about, kiddo.

Wanna know more?

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p.s. What is the difference between Fact and Theory? Why is gravity “only a theory?”

p.p.s. What type of logic does a calculator use? A computer? A horse?