LSAT 158 - Section 3 - Question 01

This is a Flaw/Descriptive Weakening question.

The argument contains one premise and one conclusion. The premise is that last year and the year before, Browning (a town, presumably) experienced significantly more rainfall in September than in July. The conclusion is predictive. It predicts that this year, Browning will probably also experience more rain in September than in July.

This is a terrible argument and you intuitively understand why. Two instances is not enough data to establish a pattern when it comes to rainfall. Imagine if this argument had a premise that said, “Meteorological records indicate that over the past two hundred years, Browning experienced significantly more rainfall in September than in July.” Well, now we’re talking. This is a pattern and it supports a prediction that this year, Browning will probably also experience more rain in September than in July. At least that would be the default reasonable position and the burden would be on the person claiming this year to be an exception to provide the evidence. Why? Because when it comes to rainfall patterns, two data points isn’t enough and two hundred is. Where is the line between enough and not enough? Is 30 data points enough? What about ten? I don’t know, ask a meteorologist. But you and I both know that two isn’t and two hundred is.

The flawed method of reasoning in this argument is recurring. This is a type of analogy flaw. The argument tries to draw a conclusion about the future based on information about the past. The central assumption is that the future is relevantly similar to the past. That assumption may be true or it may be false. It all depends on what specifically we’re talking about in the premises and the conclusion. Here, in this premise, we have past information that is scant. And so the conclusion about the future is poorly supported.

Correct Answer Choice (B) points this out. It says the argument is weak because it draws an inference about a future event on the basis of a very limited number of instances of related past events. That’s it.

Answer Choice (A) says that the argument contains a premise that presupposed the truth of the conclusion. This is a charge of circular reasoning, of begging the question. This is descriptively inaccurate. The premise is a description of past events. The conclusion is a prediction of a future event. The premise (about what already happened) does not presuppose the conclusion (about what likely will happen) to be true. Here’s a circular argument guilty of the charge in (A): Last year and the year before, Browning experienced significantly more rainfall in September than in July. Therefore, in the past two years, Browning experienced significantly less rainfall in July than in September.

Answer Choice (C) says that the argument overemphasizes the possibility that average rainfall statistics could be skewed by large rainfall in one year. What? “Overemphasizes”? But that possibility wasn’t even present in the argument. (C) is descriptively inaccurate.

Answer Choice (D) says that the argument concludes that “two phenomena are associated.” Hold up. Is that an accurate description of the conclusion? The most charitable reading of the conclusion to accommodate (D) would be to interpret one phenomenon as amount of rain and the other phenomenon as time, namely what month it is, namely whether it’s September or July. Stretching the bounds of reasonable interpretation, we can map (D)’s description of the conclusion onto the actual conclusion. That the amount of rainfall is associated with whether it’s September or July. Okay, fine. Let’s check out (D)’s premise descriptor. Merely from the claim that there are “many instances in which both phenomena are present.” Uh, no. Our interpretation is broken. Many instances? The premise contains two instances. Last year and the year before. Last year, “both phenomena were present”? What does that even mean? Last year there was rain and there was September/July? See, that makes no sense.

Answer Choice (E) says that the argument uses evidence drawn from a source whose reliability cannot readily be verified. No, that’s not descriptively accurate. We have no idea where the historical data came from. We therefore have no idea if that source’s reliability can or cannot be readily verified.