All the evidence so far gathered fits both Dr. Grippen's theory and Professor Heissmann's. However, the predictions t...

Irina on October 1, 2019

@AmMaSu,

The argument tells us that all the evidence gathered thus far supports both theories, but the theories make conflicting predictions about the outcome of the experiment. So the experiment will confirm one theory at the expense of the other. This a logical fallacy because it ignores the possibility that both theories could be wrong about the outcome of the experiment.

Let's look at the answer choices:

(A) D & J both think they know how to distinguish trees, but when they look at trees together they often disagree. Thus, at least one of them must have erroneous method.

Incorrect. The logical fallacy we are looking for is that at least one of them must be correct.

(B) Although D thinks that tree that they saw was a beech, J thinks it is an elm. J's description of the tree features is consistent with her opinion, so it must be inconsistent with D's view.

Incorrect. The argument in the stimulus says theory A predicts result X (beech), theory B predicts result Y (elm). There is no discussion of the description of the experiment features (description of the tree features) in the stimulus.

(C) D and J have been equally good at identifying trees so far. But D says this one is an elm, whereas J is unsure. Therefore, if this is elm, we know that D is better.

Incorrect. This set of facts starts off similar to the stimulus (both theories are supported by the evidence so far) but the rest of it involves entirely different logic. This set of facts is equivalent to saying that theory A says the outcome of the experiment is X, and theory B is unsure. Therefore, if it is X, then we know theory A is better. The argument in the stimulus is not saying one theory is better than the other, but concludes that if the outcome of the experiment will confirm one theory.

(D) D thinks there are more beeches than elms in the forest. J thinks he is wrong. The section of the forest examined was small, but the examination of the whole forest will confirm or deny it.

Incorrect. There is no logical flaw in this set of facts, unlike the stimulus it is not saying that we can reject or confirm either opinion based only on a small section of a forest (one experiment), but rather examine the whole forest (all the evidence).

(E) D thinks the tree is a beech, J thinks it is an elm. M is an expert in the field, unlike them, and will verify either J or D's opinion.

Correct. This answer choice parallels the logic in the stimulus. It is equivalent to saying that theory A predicts the result of the experiment is X, theory B predicts is Y, they cannot both be true. So we use an experiment (M) to confirm one of the theories. Since M could say that the tree is neither beech, nor elm, this is the same logical fallacy as we see in the stimulus.