Strengthening a conclusion that compares two alternatives

[hychu3]

Hi,

Suppose we have some observation X that we want to explain.
(For example, "numbers seem to indicate minivans are safe.")

Let A and B be possible explanations of X.
(For example, "minivan drivers are risk averse" and "minivans are inherently safer by structure.")

The conclusion of the stimulus claims that X is due to A, and not due to B.
(For example, "numbers seem to indicate minivans are safe because minivan drivers are risk averse, not because they are inherently safer.")

The question asks for a strengthener.

In this case, would eliminating another possible explanation of X strengthen the conclusion? For example, another possible explanation, C, of X could be: "vast majority of minivans are driven only in regions with virtually no automobile accident." Can eliminating C be considered as strengthening the conclusion?

I'm a little unsure because eliminating C seems to help strengthen A and B together. So, since the conclusion is arguing for A but against B, it appears that eliminating C would not necessarily strengthen or weaken the conclusion. It seems to weaken and strengthen different parts of the conclusion at the same time.

Would you say this line of reasoning is fine?

By the way, my question is inspired by PT60 Section 3 Question 21. I can see that (E) strengthens the conclusion by helping ~B only, but I'm unsure about (C) because it helps both A and B by elminating an alternate explanation.

[tommywallach]

Hey Hychu,

If you want X to lead to Y, yes it's always helpful to get rid of Z (as a cause of Y). In your example (and by the way--this conversation would probably have been best in the thread for that question, rather than here), (E) clearly strengthens the direct conclusion, whereas (C) is irrelevant to either issue (both inherent safety of vehicle and the risk-level of the average driver).

-t