Diplomat: Every major war in the last 200 years has been preceded by a short, sharp increase in the acquisition of w...

warren on July 25, 2015

Help

Somebody please explain why it is a and not b.

1 Reply

Melody on August 5, 2015

Conclusion: "arms control agreements will preserve peace."

Why? "Every major war in the last 200 years has been preceded by a short, sharp increase in the acquisition of weapons by the nations that subsequently became participants in those conflicts."

Let's diagram the premise:

If there was a major war in the last 200 years, then it was preceded by a short, sharp increase in the acquisition of weapons by the nations that subsequently became participants in those conflicts.

MW ==> IAW
not IAW ==> not MW

This argument is switching the necessary and sufficient conditions of its premise and falsely interpreting it to mean that if there is an increase in acquisition of weapons, then there will certainly be a major war. However, we know this to be false. We cannot use a necessary condition to infer any other information. Further, remember that we can look to the necessary conditions of the principle rule and its contrapositive to create a possible scenario.

So, in this case, we can have "PIAW" and "not MW" together, i.e. we can have an increase in acquisition of weapons, while not having a major war.

Answer choice (A) is correct because it points out exactly what we discussed above, that the diplomat is incorrectly switching the necessary and sufficient conditions. Let's diagram (A):

We have an unless formula. Remember, we diagram A, unless B, by negating the sufficient condition and keeping the necessary condition as is. So we would diagram this example as "not A ==> B."

So, (A) would be diagrammed:

If an event of the second type occurs (an increase in acquisition of weapons), then an event of the first type (a major war) occurs.

(A): IAW ==> MW

As you can see, we have switched the variables here, but have forgotten to negate. Thus, answer choice (A) clearly points out the flaw in diplomat's argument.

Answer choice (B) is incorrect because nowhere in the argument did the diplomat say that it is because weapons are used in war that a rapid increase in the acquisition of weapons will lead to war. We have not been given any info on what happens during a war. We merely know that when a major war occurs, it is preceded by a short, sharp increase in the acquisition of weapons.

Remember, the limit to your knowledge on the LSAT is found in the boundaries of the passage. If it is not explicitly stated, then we do not know it. Thus, we cannot say that the argument reasons in this way since we have not been given any information to back this up.

Hope that helps! Please let us know if you have any other questions.