Logical Reasoning

PT134 · S2 · Q16 Anyone who believes in extraterrestrials

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Anyone who believes in extraterrestrials believes in UFOs.

Conclusion

It’s false to believe in extraterrestrials (extraterrestrials don’t exist)

Evidence

Everyone who believes in extraterrestrials believes in UFOs. But it is a fact that UFO’s do not exist.

Evaluation

This feels like a valid argument by contrapositive. If we were given extraterrestrials → UFO, and then we learn ~UFO, then we can conclude ~extraterrestrials.

But this argument is shifting between belief and fact. If you tell me Tanya doesn’t believe in UFO’s, I can infer that Tanya doesn’t believe in extraterrestrials. If you tell me that UFO’s don’t exist, that doesn’t tell me anything about whether or not extraterrestrials exist.

Goal

We need an argument that introduces a contrapositive, tries to factually trigger the contrapositive, but shifts from beliefs to facts. Premise 1: if you believe X, you believe Y Premise 2: Y is not true. Conclusion: X is not true.

16.

Which one of the following arguments contains flawed reasoning most similar to that in the argument above?

  1. Correct

    Anyone who believes in unicorns

    Why this is right

    If you believe in Unicorns, you believe Centaurs. Centaurs don’t exist. Thus, Unicorns don’t exist.

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

    53% picked this

  2. Anyone who believes in unicorns

    Not a Flaw

    This is valid logic. This avoids the belief vs. fact flaw of the original argument.

    1% picked this

  3. Anyone who believes in unicorns

    Bad Premise Match / Bad Conclusion Match

    This doesn’t perform the belief vs. fact flaw of the original. And it doesn’t try to argue by contrapositive. It argues by way of illegal negation. Anyone who believes Unicorns, also believes Centaurs. You don’t believe Unicorns. Thus, you don’t believe Centaurs.

    0% picked this

  4. Anyone who believes in unicorns

    Weak Premise Match / Weak Conclusion Match

    This does try to argue by contrapositive, and it does shift between belief and actuality, it’s using a different standard: whether there is/isn’t good reason for belief, whether a belief is/isn’t justified. The standards of the original argument were more black and white (refuted, false) Anyone who believes Unicorns, also believes Centaurs. No good evidence for Centaurs. Thus, no good evidence for Unicorns.

    23% picked this

  5. Anyone who believes in unicorns

    Bad Premise Match / Bad Conclusion Match

    This doesn’t argue by contrapositive, it argues by illegal negation. Anyone who believes Unicorns, also believes Centaurs. Unicorns don’t exist. Thus, Centaurs don’t exist.

    23% picked this

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