Logical Reasoning

PT2 · S2 · Q20 All savings accounts are interest-bearing

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All savings accounts are interest-bearing accounts.

Conclusion (so)

Some savings accounts have tax-free interest.

Evidence

All savings accounts are interest-bearing accounts.

Some interest-bearing accounts have tax-free interest.

Evaluate

Whenever we do Parallel Flaw, the #1 thing we look for is Nec vs. Suff errors (illegal reversals / negations), and this is indeed doing an illegal reversal.

We can choose to describe the flaw conversationally or to describe the structure and pick an answer with matching structure.

The reason the conclusion is invalid is that we don't have to think that the tax-free interest-bearing accounts are savings accounts. We know there are tax-free interest-bearing accounts, but the author is assuming those accounts are savings accounts. That's how she reaches her conclusion.

Why does she assume that? Because she's getting confused by her first premise. We know that all savings accounts are interest-bearing, but she's acting like we know that all interest-bearing accounts are savings accounts (that's the illegal reversal).

So, conversationally, we could look for an answer choice where the author assumes the reverse of one of her premises.

We can otherwise take advantage of the copycat ideas and quantifiers to map out the structure of the argument.

P: All A's are B. P: Some B's are C. C: Some A's are C.

Since SOME statements are reversible, we don't care whether the SOME premise is "Some B's are C" or "Some C's are B". Ditto for the conclusion.

What matters is that the overlapping idea in the two premises is the OUTCOME of the All statement, rather than the TRIGGER.

Goal

Find an answer that performs an illegal reversal, or look for an answer that matches this structure: P: All A's are B. P: Some B's are C. C: Some A's are C.

20.

Which one of the following arguments is flawed in a way most similar to the way in which the passage is flawed?

  1. All artists are intellectuals. Some

    Bad Validity Match

    The overlapping ingredient between the two premises is "artists", which is the TRIGGER of the All statement. We want the overlapping idea to be the OUTCOME of the All statement. This argument is valid. Some great photographers are artists. All artists are intellectuals. ------------------------------------------------------------------- So some great photographers are intellectuals.

    7% picked this

  2. All great photographers are artists.

    Bad Validity Match

    Both premises are ALL statements. We wanted a mix of an ALL and a SOME. This argument is also valid. All great photographers are artists. All artists are intellectuals. Those chain together to tell us that all great photographers are intellectuals. So it's definitely true that some are.

    6% picked this

  3. Correct

    All great photographers are artists.

    Why this is right

    The overlapping ingredient in the two premises is the OUTCOME of the All claim. The author establishes that some artists are intellectuals, and then assumes that all artists are great photographers (which is a reversal of the first premise). That's how she arrives at the connection between intellectuals and great photographers. Here's how it matches our desired structure. P: All A's are B. All GP's are Artists. P: Some B's are C. Some Artists are Intellectuals. C: Some A's are C. Some GP's are Intellectuals.

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

    77% picked this

  4. All great photographers are artists.

    Bad Validity Match

    The overlapping ingredient between the two premises is "great photographers", which is the TRIGGER of the All statement. We want the overlapping idea to be the OUTCOME of the All statement. This argument is valid. Some intellectuals are great photographers. All great photographers are artists. ------------------------------------------------------------------- So some intellectuals are artists.

    9% picked this

  5. All great photographers are artists.

    Bad Validity Match

    Both premises are conditional. We wanted a mix of a conditional (All) and a non-conditional (Some). This argument is valid. All great photographers are artists. No artists are intellectuals. Together, that proves that all great photographers are not intellectuals. So it's definitely true to make the weaker claim that SOME great photographers aren't intellectuals.

    1% picked this

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