Logical Reasoning

PT115 · S2 · Q18 All historians are able to spot

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All historians are able to spot trends.

Conclusion (Thus)

Anyone who can distinguish the significant from the insignificant is a historian.

Evidence

All historians are able to spot trends.

Anyone able to spot trends is able to distinguish the significant from the insignificant.

Evaluate

When the arguments we read on Parallel or Parallel Flaw have conditional logic and repeating symbols (able to spot trends and historian and distinguishing significance all show up twice), then it lends itself well to writing an algebraic recipe for how the argument works.

All H's can spot trends. X → Y All trend-spotters can distinguish. Y → Z So, all distinguishers are H's. Z → X

It looks like the conclusion is flawed by trying to reverse the chain of logic created by the two premises.

The two premises link up, X → Y → Z

able to able to Historian → spot trends → distinguish sig vs. insig

So a valid conclusion would be saying,

able to Historian → distinguish sig vs. insig

But this conclusion is doing the reverse, saying that if you're the right side then you're the left side.

Goal

Let's look for this pattern. There should be two conditional premises that chain together. And then the conclusion should be concluding a conditional that is an illegal reversal of the endpoints of the chain.

prem 1: X → Y (X → Y → Z) prem 2: Y → Z

conc: Z → X

18.

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

  1. Correct

    All expressions used for emotional

    Why this is right

    All three claims are conditional. The two premises chain together. The conclusion does a reversal with the endpoints. prem 1: X ? Y figure of speech ? exp for emotional impact prem 2: Y ? Z exp for emotional impact ? used by poets figure of ? exp for ? used by poets speech emot impact conc: Z ? X used by poets ? figure of speech

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

    62% picked this

  2. Political systems whose laws originate

    Bad Conclusion Match

    Not all three claims are quite conditional. The first sentence is saying "Systems like X are prone to Y", but that doesn't mean X guarantees Y. If we wanted to be charitable, we could say that these two premises still chain together. polit system whose ? factionalism ? civil laws orig in legislature (prone to) disorder If the conclusion were going to match, we would want to hear: "if civil disorder, then political system whose laws originate in elected legislature". Instead, the conclusion says: "if not run by autocrats, tends to be civil disorder"

    7% picked this

  3. Animals that possess horns or

    Bad Evidence Match

    All three claims are conditional. But the two premises don't chain together. They both have the same trigger idea. possess horns ? not used for prey or antlers but intraspecies combat possess horns ? don't have the claws or antlers or fangs predators have If the premises don't give us an A ? B ? C chain, then we can't possibly replicate the illegal reversal of the original argument's conclusion.

    10% picked this

  4. No one without a deep

    Bad Conclusion/Evidence Match

    Not all three claims are conditional. The conclusion says "short story writers could have become blues musicians". That's enough of a mismatch to bail. The premises do not form a chain, either blues musician ? deep desire to communicate short story writer ? deep desire to communicate

    12% picked this

  5. People living in open and

    Bad Conclusion/Evidence Match

    Not all three claims are conditional. The first premise says "X is determined at least in part by Y". That's not conditional, so we won't get a conditional chain from the two premises, so we won't get a conclusion that is illegally reversing a chain. To the extent that these premises chain somewhat, the conclusion is actually properly going from the beginning of the chain (live in an open and democratic country) to the end (not a product of free choice). The original conclusion went from the end of the chain to the beginning.

    9% picked this

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