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

on August 26 at 10:51PM

Option A

Can someone please explain why A is incorrect? Thanks!

1 Reply

Irina on August 27 at 12:12AM

@Minerva,

The argument is a set of conditional statements:

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

AGP -> GL

(2) Gnats can only survive in wet climates.

~WC -> ~AGP
AGP -> WC

(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:

WC -> AGP

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