Logical Reasoning

PT117 · S3 · Q22 Most people who shop for

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Most people who shop for groceries no more than three times a month buy prepared frozen dinners regularly.

Conclusion (Therefore)

In Hallstown, most people buy prepared frozen dinners regularly.

Evidence

In Hallstown, most people shop for groceries no more than three times a month.

Most people who shop for groceries no more than three times a month buy prepared frozen dinners regularly.

Evaluate

When we're doing Parallel / Parallel Flaw, and the argument contains conditionals, quantifiers, or pairs of repeating ideas, it's usually a good idea to convert the argument into an algebraic recipe. If possible, we go straight to generic variables like A/B/C or X/Y/Z, but below we'll go in steps.

(Prem 1) In Hallstown, most people shop for groceries no more than three times a month. Most H's are 3max.

(Prem 2) Most people who shop for groceries no more than three times a month buy prepared frozen dinners regularly. Most 3max are FDR.

(Conc) In Hallstown, most people buy prepared frozen dinners regularly. Most H's are FDR.

We can see that all three claims are most claims, and they're trying to form this sort of chain: Most A's are B + Most B's are C --------------------------- Most A's are C

That is illegal. The only legal inferences we make with two Most claims are these: Most A's are B Most A's are B + Most A's are C Most B's are ~A ------------------- ------------------ Some B's are C More B's than A's

We can demonstrate how chaining most statements doesn't work with an analogy: Most Senators are men Most men make < $100k ----------------------------------------- Most Senators make < $100k ?

Goal

Look for an argument with two Most premises and a Most conclusion. The two premises should be trying to "chain together". The overlapping concept they share should be the beginning of one of the claims and the ending of the other claim.

22.

Which one of the following arguments has a flawed pattern of reasoning most like the flawed reasoning in the argument above?

  1. It is clear that most

    Weak Premise Match

    There's only one Most premise. The other premise is just saying "there are very few driving accidents in West Ansland". We can't repurpose that into a Most claim. (By contrast, if it had said "few of West Ansland's accidents occur in the suburbs", we could rephrase that as "Most of West Ansland's accidents do not occur in the suburbs".)

    1% picked this

  2. It is clear that John

    Bad Premise / Conclusion Match

    None of these claims are Most claims. We want all of them to be.

    2% picked this

  3. It is clear that Fernando’s

    Bad Premise Match

    There is a Most conclusion, "most of F's friends drive to school", but the two premises aren't Most claims.

    3% picked this

  4. Correct

    It is clear that most

    Why this is right

    This ends up being the only answer choice with 3 Most claims, so that's a friendly shortcut they provided for us. Do the two Most premises try to chain together with an overlapping ingredient? Most A's are B + Most B's are C --------------------------- Most A's are C Yes. We can set it up the same way. Most HC's are commute + Most commute are DS ------------------------------------- Most HC's are DS If it's hard to understand why this is flawed, consider some numbers. Suppose there are 100 drivers in HC. 60% of HC's commute. 60 commuters 6/10 of 100 60% of commuters drive sedans. 36 sedans 6/10 of 60 So 36 out of 100 people drive sedans, and yet the conclusion is saying most people drive sedans.

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

    86% picked this

  5. It is clear that most

    Weak Premise Match Valid Logic

    Only one of the two premises is a Most claim. Also, if we happened to not notice that and bothered reading the whole argument, it turns out this is actually valid logic.

    7% picked this

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