Review the excerpts below from various public and academic discussions. Determine the primary reasoning error in each excerpt and pair it with the corresponding abstract description of that logical flaw.
- Historian: During the 19th century, every time the national debt decreased, there was a subsequent increase in agricultural yields. Therefore, lowering the national debt must have somehow stimulated agricultural productivity.Concludes that one event caused another simply because the two events occurred sequentially.
- Mayor: Critics claim our city is becoming more dangerous. However, over the last five years, the percentage of crimes involving property damage has steadily decreased. Thus, property crimes are becoming less common in our city.Draws a conclusion about an absolute quantity based solely on evidence about a proportion.
- Scientist: If a planet has an atmosphere containing oxygen, it can support carbon-based life. Recent spectral analysis shows that Kepler-452b can support carbon-based life. Thus, it must have an oxygen-rich atmosphere.Takes a sufficient condition for a particular outcome to be a necessary condition for that outcome.
- Politician: The new zoning law is clearly in the public interest. After all, the public is highly interested in this controversial law, as evidenced by the massive attendance at recent town hall meetings.Trades on an ambiguity in a key term, using it in two different senses over the course of the argument.
Answer
The Historian matches the correlation/causation temporal flaw. The Mayor matches the percentage vs. number flaw. The Scientist matches the necessary vs. sufficient condition flaw. The Politician matches the equivocation flaw.
Each argument represents a distinct, classic logical fallacy. The Historian assumes causation strictly from chronological sequence. The Mayor conflates relative percentages with raw numerical totals. The Scientist commits an illegal reversal, confusing a condition that guarantees an outcome with a condition required for that outcome. Finally, the Politician relies entirely on equivocating the phrase 'public interest'.
Step-by-Step Solution
Key Concept
Flaw in the Reasoning