LSAT 73, Logical Reasoning II, Q21

QUESTION TEXT: The only songs Amanda has ever written are…

QUESTION TYPE: Parallel Reasoning

CONCLUSION: Amanda’s next song probably won’t have more than three chords if it’s not a blues song.

REASONING: Amanda has only written punk rock and blues songs. Most punk songs don’t have more than three chords.

ANALYSIS: This isn’t a rock solid argument, but it’s fairly well supported. The author ignores a third possibility: Amanda might write a song that isn’t punk or blues. But since Amanda has never done that, it’s unlikely.

To parallel this argument, you need to match the structure. A formal diagram isn’t useful, but you should be clear on the elements.

1. All have been either A or B
2. B is usually not Y
3. If next one is not A, then probably not Y.

In practice, I skimmed the answers and eliminated those that obviously differed from the structure above. Then I focussed more closely on the two that seemed to match (C and E).

All of the answers use the same terms. They refer to a family named the Guptas, who own pets: parrots and fish. The parrots are noisy.

Despite the similar subject matter, all of the answers are different. Questions like this reward you for focussing on structural factors.

Note that there are many ways of phrasing the idea that all pets owned by the Guptas were fish or parrots. The answers all phrase this idea in different ways, but the statements are logically equivalent.

___________

1. This has the wrong structure. It should have said “If the next is not A”.
   1. All have been either A or B
   2. B is usually Y.
   3. If the next is B, it will probably be Y.
2. This has the wrong structure. It should have said “if not A, probably Y”.
   1. All have been either A or B
   2. B is usually Y.
   3. If Y, probably B.
3. This is close, but it’s not quite the same. E is better. This doesn’t say “the next”. Instead, it’s talking about all pets.
   1. All have been either A or B
   2. B is usually Y.
   3. Any that is not A will probably Y.
4. This has the wrong structure.
   1. All have been either A or B
   2. B is usually Y.
   3. If next is not B, probably not Y.
5. CORRECT. This matches exactly.
   1. Either A or B.
   2. B is usually Y.
   3. If next one is not A, it will probably be Y.
    
   Note: The fact that the stimulus said “not involve” and this said “will be noisy” is not significant. Putting things in terms of “not” isn’t a structural issue, since you can put any “not” statement in a positive form. For example, you could say “noisy” = “not quiet.”
    
   Don’t focus on words like “not”. Focus instead on whether a key term was or was not negated. In this argument, Y wasn’t negated in the stimulus or in the correct answer.

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