No fish is a mammal — Syllogisms Aptitude Question
No fish is a mammal: Statements: No fish is a mammal. All whales are mammals. Conclusions: I. No whale is a fish. II. Answer and worked solution on CodeKairo.
- Topic: Syllogisms
- Section: Logical Reasoning
- Difficulty: Medium
- Time target: 75 seconds
Question
Statements:
- No fish is a mammal.
- All whales are mammals.
Conclusions: I. No whale is a fish. II. Some mammals are whales.
Which conclusion follows?
Options
- Only I
- Only II
- Both
- Neither
Show the answer and the worked solution
Correct answer: C. Both
Worked solution
- Whales ⊂ mammals, and mammals exclude fish entirely, so no whale is a fish: I follows.
- Whales exist and are mammals, so some mammals are whales: II follows.
Answer: Both.
The idea
'All A are B' plus 'no B is C' gives the strong 'no A is C'. It is one of the few combinations that supports a universal negative.
Shortcut. I is the stock 'all + no → no' result. The point to catch is II: an 'all' statement always converts to a 'some' in reverse, so 'all whales are mammals' guarantees 'some mammals are whales'.
Common trap. "Only I" — rejecting II because the statements speak of 'all' whales and never mention 'some'; a valid 'all' always licenses the weaker reversed 'some'.