PrepTest 141

Incorrect. The conclusion is that Lemaitre's theory is inadequate, so it's not appealing to his expertise. And the alternative theory isn't attributed to anyone, so this argument isn't making an inappropriate appeal to an expert.

Incorrect. The conclusion is about Lemaitre's theory and inadequacy—the theory is still referring to the same theory, and the argument never before discusses inadequacy, so this answer is incorrect.

Incorrect. The argument never assumes causality—it simply raises a prediction that flows from a theory that happens to be true.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Errors in Reasoning

Stimulus Summary:
Lemaitre's theory correct → Galaxies accelerating apart
Galaxies are accelerating apart
However, there's another theory that makes the same prediction
Therefore: Lemaitre's theory is inadequate

Answer Anticipation:
The Science Writer here raises two competing theories that make the same prediction that turned out to be true. From this, the Writer concludes that one of the theories is "inadequate." That term isn't defined, but the author is treating the viability of a competing theory (it, too, made a correct prediction) as providing some type of evidence against Lemaitre's theory. That's not true, though. While the accelerating galaxies don't allow one theory to be supported over the other, it doesn't provide evidence against those theories, and it does provide evidence that they're better theories than other theories that don't make the same prediction.

Answer Explanation:
This answer choice highlights that two competing theories making the same prediction don't provide evidence against each other. While two theories making the same prediction means that evidence supporting that prediction can't help determine between the two theories which is correct, it doesn't mean that either theory is inadequate, either.

Key Takeaway:
Competing theories are used frequently on the LSAT, and there's a lot of subtlety involved in the logic behind them. In this question, we see that having two competing theories that make the same correct prediction strengthens those theories against other theories, but it has no effect on the theories themselves. Here, Lemaitre's theory and the oscillating universe theory both made a valid prediction, so both are supported equally by this observation, and any conclusion that either theory is worse off is incorrect.

Incorrect. The stimulus doesn't get into the explanations (or their number) for the phenomenon in question (the acceleration of the galaxies)—for all we know, the oscillating universe theory could also be based on an explosion that formed the universe. And just because the Writer only raises two theories doesn't mean that there aren't others out there.