Enter the world of GMAT logic. In the Critical Reasoning section, one of the most important things you can do for solid GMAT prep is to embrace the counterexample*.

Finding counterexamples is one of the most fundamental tricks used to highlight and isolate the assumptions inherent in the argument in question.

How exactly do you construct a counterexample? Well, basically, your responsibility is to be the annoying kid in Religion class.

“Teacher, if God is all-powerful, can He make a rock so big that He can’t lift it?”

That kid understands the limitations of an argument.

In short, he or she agrees with all premises of the plan, but finds a conclusion that spectacularly fails these premises.

This is what you need to learn to do. How do you do this?

Enter conspiracy theories. According to the late counterculture philosopher Robert Anton Wilson, conspiracy theories are an excellent way to sharpen your logical skills (and have a laugh).

Coming up with them? Of course not. Debunking them!

This applies directly to GMAT Critical Reasoning. Take the normal-seeming premise that is presented.

For example:

“The city has decided to halve the amount of ash produced at the local incinerator. To this end, the city has decided to separate enough recyclables from collected garbage that the number of trucks of garbage sent to the incinerator will be halved. This will clearly reach the city’s goal of producing half the quantity of ash as previously produced.”

The conclusion is that reducing the number of trucks will reduce the amount of ash. It seems plausible.

So what is wrong with the argument? Can you tell? Let’s look a little bit deeper.

To do this, it’s time to think about it like the tinfoil-hat crowd.

These people are absolute experts at taking a series of established facts and they weave a completely ludicrous story–involving aliens, secret societies, or the ghost of James Dean–around those facts!

But there’s no reason to involve aliens here.

Simply use a basic, sane version of their thinking.

That is, the classic reductio ad absurdum: assume the negation of the conclusion and work backward to find the flaw in the argument.

That is, how is it possible for the facts, as presented, to be correct and yet for the conclusion to be false?

With our example, simply assume that the amount of ash stays the same even if the number of trucks is halved.

How is this possible? A couple of ways come to mind. Either make the trucks twice as big, or propose that the non-recyclables–that is, the leftover materials—produce twice as much ash by volume as the recyclables.

The next step is to plug the hole. The best way to do this is with extra facts.

All we need to verify in this case is that the trucks will produce no more ash per truckload than they did previously.

Remember that all life depends on a certain number of assumptions.

To succeed in your GMAT Critical Reasoning prep, you simply need to understand what assumptions are reasonable to make for the exam.

This takes time, patience, and detailed study of CR questions and answers.