Logical Reasoning

PT111 · S3 · Q22 The folktale that claims that a

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The folktale that claims that a rattlesnake’s age can be determined from the number of sections in its rattle is false, but only because the rattles are brittle and sometimes partially or completely break off.

Conclusion

If a rattlesnake's rattles weren't so brittle, then you could reliably determine a rattlesnake's age simply by counting the number of sections in its rattle.

Evidence

Every time a rattlesnake molts, it forms a new section.

Evaluation

This question is really hard. The "So" and "because" telegraph that they want us to care about the argument in the last sentence. The question stem looks like Sufficient Assumption (conclusion properly drawn) but is really Necessary Assumption.

The argument is making a leap from to . By transitive property, the author seems to be thinking we can tell a snake's age by knowing how many times it molted.

Why does the number of times a snake molted tell us the snake's age?

The author must be assuming there's some relationship between molting and age (like the snake molts once a month, or once a year, or once every three years, etc.)

Goal

Look for an answer saying that the author is assuming there's some "reliable" relationship between when a rattlesnake molts and its age.

22.

Which one of the following is an assumption the argument requires in order for its conclusion to be properly drawn?

  1. Rattlesnakes molt exactly once a

    Too Specific

    If this were Sufficient Assumption, this answer choice would effectively prove the conclusion. A rattlesnake with 10 sections would be 10 years old. However, the author just needs to assume there is SOME reliable relationship between molting / age. He doesn't need that relationship to be once per year. If snakes molted twice a year, that would still give a reliable way to translate # of sections into age. A snake with 10 sections would be 5 years old.

    33% picked this

  2. The rattles of rattlesnakes of

    Too Strong: Identical

    The author doesn't need them to be identical. She needs them to all have rattles that reflect the correct number of sections made (in this hypothetical non-brittle world). But it doesn't matter if some of them are brown, some are black, some are red, etc.

    1% picked this

  3. Rattlesnakes molt more frequently when

    Opposite

    The author needs to assume there is a consistent relationship between molting and time. If there's an erratic one that varies by age or weather or whatever, that would hurt his reliable measurement of time.

    1% picked this

  4. The brittleness of a rattlesnake’s

    Out of Scope: Brittleness

    The author's argument is about a hypothetical world in which the snake's rattle is not brittle, so there's no reason in that hypothetical world where the snake's rattle isn't brittle the author would be making any assumptions about the brittleness of the rattle. To put this another way, if you negate this, and you say that brittleness of rattle is correlated with length of life, that doesn't hurt the author's argument. She is arguing that counting numbers of sections is one reliable way to tell the age of a snake. It doesn't hurt her argument if there's another way to tell the age of a snake (via the brittleness of its rattle).

    19% picked this

  5. Correct

    Rattlesnakes molt as often when

    Why this is right

    One of the all-time hardest correct answers. Since the author is assuming there's a reliable relationship between molting and age, she has to assume that the rate of molting doesn't vary with malnutrition, or funky climate, or changes in predator/prey dynamics, or mating habits, etc. If she thinks that all we need to see is the number of sections, to determine a snake's age, then she is assuming that molting happens at a constant interval. If we negated this, we could object to the argument by saying "if the rate of molting is different, based on whether a snake was well fed or starving, then we couldn't really reliably gauge a snake's age from its number of sections. A snake with 10 sections might be 5 years old if it's been well fed or up to 10 years old if it's been malnourished."

    Skill tested: Necessary Assumption · how this choice captures the argument's function is the move to repeat next time.

    46% picked this

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