QUESTION TEXT: If the law punishes littering, then the…
QUESTION TYPE: Flawed Parallel Reasoning
CONCLUSION: The city doesn’t need to provide trash cans.
REASONING: If the city punishes littering, then the city must provide trash cans. But the city doesn’t punish littering.
ANALYSIS: This argument makes a mistaken negation. The author incorrectly assumes that if a sufficient condition isn’t true, then a necessary condition isn’t true.
It’s possible that the city should provide trash cans, even if the law doesn’t punish littering. Maybe the city has an obligation to help keep the city clean.
Here’s the premise:
P ➞ TC
Here’s the incorrect negation:
P ➞ TC
You’re only allowed to negate and reverse a premise. That gets you the contrapositive.
___________
- This is an incorrect reversal. H ➞ O turned into O ➞ H.
- This is almost a good argument, but not quite. The argument has given good evidence that Jenny’s birthday party hasn’t started yet.
But it might be her birthday. The balloons could be coming later. Or maybe her birthday party is not on her birthday.
- This is also an incorrect reversal. S ➞ A turns into A ➞ S.
- CORRECT. This is an incorrect negation. L ➞ M becomes L ➞ M.
- This is a good argument. It uses the contrapositive of the premise to prove the law isn’t being enforced.
“No one in jail ➞ law not enforced.”
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