#23 - A species in which mutations frequently occur will

[Administrator]

Complete Question Explanation

Parallel Flaw—SN. The correct answer choice is (C)

The premises in the stimulus provide two conditional rules: first one states that if there are frequent mutations in a species, there must be new evolutionary adaptations in each generation, whereas the second one suggests that if a species survives dramatic environmental changes, there must be new evolutionary adaptations in each generation. Both premises contain the same necessary condition, while their sufficient conditions differ. The conclusion attempts to connect these conditions into a third conditional rule. However, there is no valid connection between them, which is why the conclusion is invalid.

The erroneous pattern of reasoning can be diagrammed as follows:

• Premise: Frequent mutations New evolutionary adaptations in each generation
  
  Premise: Species survive changes New evolutionary adaptations in each generation
  
  Conclusion: Frequent mutations Species survive changes

The correct answer should contain two conditional statements in the premises sharing the same necessary condition. This is a unique construction for a conditional argument, and so the Premise Test is the most effective approach to eliminating answer choices. Any answer choice that does not contain two conditional premises with identical necessary conditions should be immediately eliminated.

Answer Choice (A): This answer choice does not match the flawed reasoning in the stimulus. First of all, the two conditional rules in the premises do not have identical necessary conditions. Also, the flaw in this answer choice is a different kind of error than the error in the stimulus. One of the premises concerns “walls,” while the other premise deals with “stone walls.” It is invalid to make a conclusion about one based on evidence concerning the other.

Answer Choice (B): There is only one conditional rule in the premises, so this answer choice does not match the Premise Test. Also, this answer choice is valid so it fails the Validity Test. The second sentence is a restatement of the conditional rule in the first sentence. While the language is different, the logic of the original premise did not change. The logic can be diagrammed as follows:

• Premise: Different Audience Different Reaction
  
  Premise: Different Audience
  
  Conclusion: Different Reaction

Answer Choice (C): This is the correct answer choice. According to the first premise, a perfectly honest person must always tell the truth. The second premise suggests that a morally upright person must always tell the truth as well. Both of these premises share the same necessary condition. The conclusion attempts to connect the two sufficient conditions in an invalid conditional relationship. This matches the stimulus. The logic of this answer choice can be diagrammed as follows:

• Premise: Perfectly Honest Tell The Truth
  
  Premise: Morally Upright Tell The Truth
  
  Conclusion: Perfectly Honest Morally Upright

Answer Choice (D): This answer choice is actually valid and so it fails the Validity Test. The answer choice properly connects two conditional rules into a valid chain relationship. The logic can be diagrammed as follows:

• Premise: Productive Herb Garden Soil Well Drained
  
  Premise: Soil Well Drained Good Soil
  
  Conclusion: Productive Herb Garden Good Soil

Answer Choice (E): Unlike the stimulus, the premises in this answer choice can be connected to form a valid conditional chain. However, the answer choice is flawed because it switches from “healthful diet” in the premises to “being healthy” in the conclusion. The logic can be diagrammed as follows:

• Premise: Healthful Diet Well Balanced Diet
  
  Premise: Well Balanced Diet Fruits and Vegetables
  
  Conclusion: Being Healthy Fruits and Vegetables

[al_godnessmary]

I just want to check how the diagramming works to see if I made any mistakes. Thanks!

This is what I got for the stem:

Flaw: Mistaken Reversal for second condition

Mutations Freq Occur Each Generation Adapt

Survive Each Generation Adapt

Mutations Freq Occur Survive (INCORRECT INFERENCE BECAUSE NOTHING LINKS THESE TWO)

And then for answer C...

Honest Every Sit Truth
Morally Upright Every Sit Truth
Honest Morally Upright

And therefore it matches the flawed reasoning because it starts with two different things leading to the same thing, and concludes that the two different things therefore cause each other?

[Robert Carroll]

al,

Everything looks perfect in the diagramming and in your reasoning. Way to go!

Robert Carroll

[ashpine17]

i need someone to check my diagramming for A because I cannot hold all the variables in my head. PB---> SS (support stone) T(sturdy)---> PB, T--->SS
so valid?

[Jeff Wren]

Hi ashpine,

This answer can be tricky to diagram, and you definitely should carefully diagram it rather than trying to keep the variables in your head.

The most important thing to notice in this argument is the shift in terms from "stone wall" in the first premise to just "wall" and "walls" in general in the second premise and conclusion (meaning these walls may not necessary be made of stone).

This shift is easy to miss but is very important and turns out to be the reason that this argument is not valid.

When diagramming this argument, you need to diagram "stone wall" as a different term than "wall" or "walls."

In the first premise, you could diagram the sufficient as one term "SWPB" for "if stone wall properly built" or you can separate it into two terms linked by the word "and." For example, "SW" + "PB" (for" if stone wall and properly built.")

In the second premise, you could diagram the sufficient as "Stdy. W" for "sturdy wall" or separate them out "Stdy." and "W" for "if sturdy and wall." The important thing is that you don't diagram "sturdy wall" the same way as "stone wall," because they are different terms.

The conclusion would be Stdy. W -> SS (for "stones supporting other stones").

This is invalid because "stones supporting other stones" is only necessary for properly built stone walls, not all properly built walls. For example, if you had a properly built wooden wall, it wouldn't need stones supporting other stones.