Gecko lizards are found in any environment where there is an abundant population of gnats. Gnats can survive only in ...

Minerva on August 26, 2019

Option A

Can someone please explain why A is incorrect? Thanks!

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Irina on August 27, 2019


The argument is a set of conditional statements:

(1) Gecko lizards are found anywhere where there is an abundant population of gnats.


(2) Gnats can only survive in wet climates.

~WC -> ~AGP

(3) Because there are no lizards, there must be not an abundant population of gnats.

~GL -> ~APG

This is a valid inference as it is a contrapositive of premise (1)

(4) The climate must not be wet.

~AGP -> ~WC

This is in an invalid inference, it is a mistaken reversal of premise (2). The only way this inference could be valid is if this statement was true:


If the climate is wet, then it has an abundant population of gnats.

Since the argument erroneously relies on this premise to form its conclusion, the correct answer choice is (B).

(A) is incorrect because the argument does not require that:

~AGP -> ~GL is true.

The argument makes a valid inference:

~GL -> ~AGP from

AGP -> GL.

Does that make sense?

Let me know if you have any further questions