Logical Reasoning

PT112 · S3 · Q19 My father likes turnips

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My father likes turnips, but not potatoes, which he says are tasteless.

Conclusion (so)

It is not true that whoever likes potatoes likes turnips. rephrase: Some people like potatoes but don't like turnips.

Evidence

My father likes turnips but not potatoes.

Evaluate

The flaw here, in short, is that the evidence is irrelevant to the conclusion. The argument is trying to prove that some people who like potatoes don't like turnips.

But the evidence is an example of someone who likes turnips but doesn't like potatoes.

Goal

Since the error here is that the example presented in the evidence is the reversed version of what the author is trying to prove, we can represent this flaw symbolically:

CONC: It's not true that anything that's X is Y. (i.e. some X's are not Y)

EVID: This example is Y but not X.

19.

The flawed reasoning in the argument above most closely resembles that in which one of the following?

  1. This book is not a

    Weak Conclusion Match

    This conclusion is objecting to the claim that "some P's are E". If it's denying that "some P's are E", then it's trying to prove "All P's are not E". The original conclusion is objecting to the claim that "all P's are T's, so it's trying to prove "some P's are not T". That's reason enough to bail from this answer.

    6% picked this

  2. Correct

    Although this recently published work

    Why this is right

    This matches up with what we were looking for. The conclusion is trying to disprove a universal, so the author just needs to establish one counterexample. But his evidence provides the negated version of the counterexample we're looking for. CONC: It's not true that anything that's X is Y. (i.e. some X's are not Y) It's not the case that all novels have more than 75. (some novels have 75 or fewer pages) EVID: This example is Y but not X. This thing is more than 75, but not a novel.

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

    61% picked this

  3. All ornate buildings were constructed

    Bad Conclusion Match

    The original conclusion is refuting a universal statement. CONC: It's not true that anything that's X is Y. (i.e. some X's are not Y) This conclusion is affirming a truth about one specific thing: this house was built before the 20th century That's enough of a mismatch to bail.

    1% picked this

  4. Erica enjoys studying physics, but

    Valid Logic Bad Evidence Match

    This argument isn't flawed. Like the original, its conclusion is refuting a universal. CONC: It's not true that anything that's X is Y. (i.e. some X's are not Y) It's not true that all who enjoy studying physics also enjoy studying math. (i.e. some ppl who enjoy physics don't enjoy math) However, in the original, the evidence presented a counterexample with inverse terms. Instead of saying "this is an example of something that is X but is not Y", it said ... EVID: This example is Y but not X. In this answer choice, the premise is actually the logically valid form. To disprove that "all who enjoy physics also enjoy math" we need an example of someone who enjoys physics but not math. We get just that, thanks to Erica. In order for this answer to match, you'd want the premise to say "Erica enjoys studying math but doesn't enjoy studying physics".

    28% picked this

  5. People who do their own

    Bad Conclusion Match

    The original conclusion is refuting a universal statement. CONC: It's not true that anything that's X is Y. (i.e. some X's are not Y) This conclusion is affirming a truth about one specific thing: my next-door neighbors do their own oil changes. That's enough of a mismatch to bail.

    4% picked this

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