## PrepTest 73, Logical Reasoning 1, Question 5

### Transcript

Question five, when a question asks us for the flaw that's in an argument, it's a flaw question. Which means that we have to describe the problem that's in the argument. There's an error somewhere in the logic of what we've been given. But before we can find that error, we have to figure out what the argument says. Which means understanding its conclusion and its evidence.

The conclusion of this argument comes at the end, Lemaitre's theory has to be considered inadequate. The first half of the argument basically is the first piece of evidence. So Lemaitre argues that the universe began with the explosion of a primeval atom, a singular point of infinite gravity in space and time. If you're worried about understanding that, don't be.

We don't have to understand science on the test, we just have to understand logic. So Lemaitre had a theory, and if his theory is correct, our current observations should reveal galaxies accelerating away from one another, and that's what we do see. But the second piece of evidence, there's another theory out there, another theory that says the same thing.

And that's why they say that Lemaitre must be wrong. There is another theory that says the same thing as his theory. Now if that strikes you as not a very good argument, congratulations, it's not a very good argument. On a flaw question, we're going to be given a bad argument. Just because there's another theory out there that says the same thing as this theory, why does that mean the original theory is bad?

The flaw in the argument is, they don't give any reason to explain why, just because there's another theory out there that predicts the same thing, we have to reject the original theory. So that's the flaw we're gonna be looking for in the answer choices. So answer choice A says that the conclusion is derived partly from assertions attributed to a purported expert, but there isn't a purported expert here.

Sure, Lemaitre is an expert, but the argument isn't using an expert to disprove Lemaitre. There's no expert in the evidence, so answer choice A can't be the answer. Answer choice B says that the conclusion is based on a shift in meaning of a key term. There aren't any key terms shifting in meaning here.

There's nothing that the argument uses in one way in one sentence, and then in another way in another, so it can't be answer choice B. Answer choice C talks about causal connections. This argument has nothing to do with causal connections, so it can't be our answer. Answer choice D says that the writer fails to see that one theory is correctly predicting data can't itself constitute evidence against an alternative theory.

And that's what we're looking for, the one theory that correctly predicts observed data is the oscillating universe theory. And just because it correctly predicts the data doesn't mean that the alternative theory or Lemaitre's theory is wrong. So answer choice D describes the error that we saw from the very beginning, it is our answer.

So what's wrong with E? E says that the science writer presumes that there are only two possible explanations. This argument isn't built off an assumption that there are only two possible explanations. Now granted, there are two explanations, but the author doesn't say that those are the only two explanations that could ever exist.

So E is not an error that this argument commits. The answer must be answer choice D.