Logical reasoning PrepTest 155 · Section 1 · Question 2

Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen with a Necessary Premise

Stimulus Summary:
A new documentary, Train Stories, attracted a small audience on its first night (Thursday) and a "not significantly smaller" audience on its second night (Friday). Therefore, most of audience on the first night must have liked it enough to watch it again on the second night.

Strategy Overview:

1. Argument or facts? Always argument, so identify premises and conclusions of argument
2. Anticipate why the premises are not enough to show that the conclusion is true
3. Use anticipations to select the answer choice that:
   1. Strengthens the conclusion of the argument, and
   2. Is necessary for the conclusion of the argument
      1. Can use "negation test" to double-check: if this answer choice isn't true, does the conclusion become untrue as well? If so, it's necessary for the conclusion of the argument, and it is the correct answer

Answer Anticipation:
On Strengthen with a Necessary Premise questions, our job is to find the answer choice that: (a) strengthens the conclusion of the argument and (b) must be true to draw the conclusion. Finding an answer choice that matches both criteria is, at first, very challenging for many test-takers.

But after completing many of these questions, observant LSATers start to see a pattern. For most Strengthen with a Necessary Premise questions, the author will introduce a "new," important idea in the argument's conclusion. The premises will not touch on this "new" important idea. In introducing this new idea, the author creates a gap between the premises and conclusion. The correct answer will address the gap between the premises and the new idea, often simply linking the two concepts. After all, bridging the gap — at least partially — will strengthen the argument, and showing that the gap is fixable is necessary to draw the conclusion.

Aside from this question apparently being written by someone who only watches PBS, the biggest thing that jumps out of the conclusion is the new idea of "most of the first night's liked it enough to tune in again the next night." There's a logical gap between "the audience didn't shrink" (premises) and "most of the first night's audience watched again" (conclusion). After all, there could be many other reasons why the audience didn't shink. Maybe the second night attracted an entirely new audience who didn't watch the first night. The correct answer choice will address this gap, either by linking the two concepts (e.g., "the audience didn't shrink because most of the first night's audience tuned in again") or by eliminating an alternative explanation (e.g., "the Friday audience didn't consist of many viewers who hadn't seen the show Thursday night").

Finally, we can double-check answer choices with the negation test if we need to. To apply the negation test, we can simply ask, "If this answer choice weren't true, does the conclusion become untrue as well?" If so, that answer choice is necessary for the argument's conclusion. If the conclusion could still be true, then that answer choice is wrong.

Answer Explanation:
Right away answer choice (A) provides an exact match for our anticipation. This answer choice fills the logical gap by clarifying that Friday's audience didn't shrink because most of Thursday's viewers watched it again.

Moreover, the negation test confirms that this answer choice is necessary to the argument. Suppose that most of Friday's viewers had NOT watched on Thursday. In that case, could we conclude that most of the viewers who watched the program on Thursday liked it enough to tune in again on Friday? Of course not. In that case, most of Thursday's audience would have declined to watch on Friday. Therefore, (A) is necessary to the argument and is correct.

Key Takeaway:
Experienced LSATers simply Strengthen with a Necessary Premise question by focusing on the gap between the premise and the new term in the conclusion. On this particular question, only one answer choice addressed that gap at all.

Whether viewers liked the program on the second night is irrelevant. The conclusion is about what the first-night viewers thought of the train documentary. So, sorry second-night viewers, we don't care what you thought of the show.

Again, the argument's conclusion is about how viewers felt about the first installment of the documentary, not the second. Whether viewers liked the second installment more or less than the first would not affect this argument's conclusion.

This answer choice tells us about the people who only tuned in to the first night of the documentary. It's not difficult to see the appeal in this answer choice. It tells us that those who only tuned in to the first night of the documentary couldn't watch TV on night two. And that might suggest to some overly generous test-takers that it wasn't the case that these viewers dropped out because they hated the train documentary. And that, in turn, may suggest that those who watched both nights liked the train documentary.

However, both of those leaps are unwarranted. First, nothing here suggests that those who only watched night one enjoyed the doc. A person could simultaneously be unable to watch television and have no intention of watching this particular train documentary if they were able to watch television. Second, even if they did love the train doc, that wouldn't tell us that most of the people who watched the first night also watched the second night.

This is not relevant to the argument's conclusion. Whether these viewers generally liked documentaries or not, the question is, did most of them like this particular documentary enough to watch the second part? This answer choice doesn't strengthen or weaken the conclusion, and it is incorrect.