GMAT Verbal Tip: Lessons from the Matrix — Causality in Critical Reasoning
In “Matrix: Reloaded,” the Merovingian says: “You see there is only one constant. One universal. It is the only real truth. Causality. Action, reaction. Cause and effect… We are all victims of causality. I drank too much wine, I must take a piss. Cause and effect.” Mero would have done very well on GMAT’s critical reasoning questions.
Tracking causality on CR questions, and to lesser extent on RC questions, is extremely important. It is one of the most common logical obfuscation devices employed on the GMAT, both in the premise and in the answer choices. Luckily, dealing with causality is straightforward as long as you follow the following guidelines:
- Note every cause and effect in the premise on your scratchpad.
- Cause and effect are not interchangeable.
- P->Q does not imply Q->P, but does imply “not Q -> not P”.
For example, if given that “The African fire dragon parasite has been conclusively shown to come from larva contaminated drinking water”, you would note that “Contaminated water -> Parasite”. Don’t forget that some effects are causes for other effects, so you may need to note a chain of causality (X -> Y -> Z).
In our previous example it would be a mistake to write “Parasite -> Contaminated water”; we want to be meticulous about tracking our causes and effects. The reason for this is…
In math logic speak, the former is called a converse, and the latter, the contrapositive. The deal with the converse is that it is not necessarily true even if the original statement is true. Contrapositive, on the other hand, is always true if the original statement is true.
To see why this is, consider the following premise: “If Artem sees the cake, then the cake will be eaten.” (ie, P->Q)
Converse: “If the cake was eaten, then Artem saw the cake.” (Q->P)
But what if someone else ate it before I saw it?! Therefore, this statement is not necessarily true. In other words, there may be causes other than P for the same effect Q.
Contrapositive: “If the cake wasn’t eaten, then Artem didn’t see the cake.” (not Q -> not P)
True – I totally would have eaten it if I did see it.
Watch out for converses in answer choices, since they will sound like great options, but will not necessarily be logically sound. Contrapositives, on the other hand, are always a valid inference from any causality statement.