QUESTION TEXT: Local resident: An overabundance of algae must…
QUESTION TYPE: Flawed Reasoning
CONCLUSION: An excess of algae is bad for the small fish in the pond.
REASONING: The gardener has seen lots of algae whenever he has seen many small fish wash up dead on the shore.
ANALYSIS: The gardener is confusing correlation and causation. He could have also said that dead fish cause algae to bloom. Just because two things happen together doesn’t mean one causes the other.
It’s possible there is something in the water which both kills fish and helps algae grow.
Note that the gardener says nothing about larger fish. There may not even be any in the pond; the gardener could be comparing the pond’s “smaller” fish to the larger fish found in rivers and oceans.
- The gardener didn’t say anything about larger fish. Maybe there aren’t any in the pond. The gardener could have said “smaller fish” just to make clear that the fish were small compared to bigger fish that live in lakes and oceans.
In any case, there is justification: small fish from the pond are clearly dead.
- The gardener was only talking about the pond. He might agree that algae can’t harm fish in a river or big lake.
- The gardener didn’t say whether algae hurts larger fish too. He only talked about the pond, and there may be no large fish in the pond.
In any case, the gardener explicitly said that smaller fish are vulnerable, and implied larger fish might not be.
- CORRECT. There could be something in the water which hurts fish but which nourishes algae.
- The gardener didn’t say what happens when the pond has a shortage of algae. He might agree that it would be bad too. But perhaps the pond has never had an algae shortage so far.
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