Logical ReasoningDifficulty: Medium

PT2 S2 Q20 Explanation

All savings accounts are interest-bearing

A free, expert breakdown of this official LSAT Logical Reasoning question.

TopicsParallel Flaw

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Stimulus

All savings accounts are interest-bearing accounts. The interest from some interest-bearing accounts is tax-free, so there must be that have tax-free interest.

What this question is testing

Parallel Flaw

Premise 1

All savings accounts are interest-bearing.

Premise 2

Some interest-bearing accounts have tax-free interest.

Conclusion

Therefore, some savings accounts have tax-free interest.

Evaluate

Picture two circles. The bigger circle is "interest-bearing accounts." Inside that bigger circle is a smaller circle, "savings accounts" (because all savings accounts are interest-bearing).

Now somewhere else in the bigger circle, there are accounts with tax-free interest. But "somewhere else" is the key phrase. Those tax-free accounts could be in the part of the bigger circle that does not overlap with savings accounts at all — like CDs or money market accounts. The argument assumes the tax-free ones must overlap with the savings-account circle, but nothing in the premises forces that.

That is the flaw: All A are B. Some B are C. So some A are C. The "some B" might not be A at all.

Goal

Find the answer with the same structure: All [smaller group] are [bigger group]. Some [bigger group] are [property]. Therefore, some [smaller group] are [property].

Reading along? Open the full official question in LawHub — we show a fragment here and keep the reasoning in our own words.

The question
20.

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

Answer choices

  1. Bad Validity Match7% picked this

    All artists are intellectuals. Some great photographers are artists. Therefore, some great photographers

    This argument is valid. All artists are intellectuals. Some great photographers are artists. So those photographers (who are artists) must also be intellectuals. The structure is "All A are B. Some C are A. So some C are B" — and this is logically airtight. We need a flawed argument matching the original's flawed structure.

  2. Bad Validity Match6% picked this

    All great photographers are artists. All artists are intellectuals. Therefore, some great photographers

    This argument is also valid. All great photographers are artists. All artists are intellectuals. So all great photographers are intellectuals — and certainly some are. The structure transmits the property cleanly through universal claims. The original's flaw came from a "some" premise pointing to an unspecified subset of the larger group; this argument has no such weakness.

  3. Correct77% picked this

    All great photographers are artists. Some artists are intellectuals. Therefore, some great

    Why this is right

    This matches the original's flawed structure exactly. All great photographers are artists (All A are B). Some artists are intellectuals (Some B are C). Therefore, some great photographers are intellectuals (Some A are C). The "some artists" who are intellectuals could be artists who are not photographers at all — say, sculptors. The argument has not actually shown any photographer to be an intellectual. Same flaw as the original: the "some B are C" premise tells us nothing about which B's, so it cannot be moved over to A.

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

  4. Bad Validity Match9% picked this

    All great photographers are artists. Some great photographers are intellectuals. Therefore, some artists

    This argument is valid. All great photographers are artists. Some great photographers are intellectuals. The "some great photographers" who are intellectuals are also artists (since all photographers are artists), so it follows that some artists are intellectuals. The structure is "All A are B. Some A are C. So some B are C" — which is fine. The original's flaw was different.

  5. Bad Validity Match1% picked this

    All great photographers are artists. No artists are intellectuals. Therefore, some great photographers must

    This argument is valid. All great photographers are artists. No artists are intellectuals. So no great photographers are intellectuals (and thus some are not). The structure uses a universal-negative premise, which is not the original's pattern, and it follows correctly. Not a parallel flaw.

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