Logical reasoning PrepTest 122 · Section 1 · Question 10

Incorrect. This relationship doesn't have to be understood in order to establish a relationship. You probably don't understand why dumping water on a laptop causes it to short out, but you're still not going to pour your drink on your computer!

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen with Necessary Premise

Stimulus Summary:
Experiment — One gene in flies was altered, and those flies didn't have UV vision.
Conclusion — Any fly without UV vision must have damage to that gene.

Answer Anticipation:
The experiment established that all flies with an altered gene didn't have UV vision—or Altered gene → not UV vision. The conclusion states that all flies without UV vision has damage (an alteration) to that gene—or not UV vision → Altered gene.

That's an illegal reversal! However, we're not used to seeing illegal reversals/negations in Strengthen with Necessary Premise questions. When this happens, what should we anticipate as the correct answer?

Well, illegal reversals are flawed because they treat a necessary condition as sufficient (or vice versa). In other words, they assume that there are no other sufficient conditions for the given necessary condition. The correct answer will therefore likely rule out some other potential factor that would result in the lack of UV vision for flies—another gene, or a non—genetic factor that could affect vision.

Answer Explanation:
This answer rules out another potential sufficient condition for the lack of UV vision in flies—other genes. If there are other genes that are required for UV vision cells to form, then those genes might be the reason for certain flies to lack the ability, not the gene in question. This answer is therefore required for the argument to hold true and is correct.

Key Takeaway:
We viewed this question through the lens of sufficient/necessary logic, but it could just as easily be viewed through a phenomenon/explanation or cause/effect lens. All of these types of arguments have one thing in common—they generally pick one option" (explanation, cause, or sufficient condition) over others, and thus they're flawed if they don't rule out alternatives. All of these types of arguments, therefore, tend to have answers that discuss these alternatives.

Incorrect. The conclusion is about flies of the given species, not all flies, so this answer is out of scope.

Incorrect. The conclusion is limited to discussing UV vision, so other impacts of the altered gene are out of scope.

Incorrect. This answer is the opposite of what we're looking for—it establishes an alternative factor in UV vision, it doesn't rule one out. This answer weakens the argument, so it can't serve as a necessary assumption to it.