Accept every statement below as true, whatever the real world says. Which of the conclusions must then be true?
Statements:
1. No cat is a dog.
2. Some dogs are monkeys.
Conclusions:
I. Some monkeys are not cats.
II. No dog is a cat.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Both conclusions I and II follow
A conclusion follows only if it is true in every diagram that fits the statements. One diagram in which a conclusion is false is enough to reject it.
“No cat is a dog”: the circles of cats and dogs do not touch
“Some dogs are monkeys”: the circle of monkeys overlaps the circle of dogs
Conclusion I: Some monkeys are not cats. — Follows. The monkeys that are dogs can never be cats, because no dog is a cat. So at least those monkeys are not cats.
Conclusion II: No dog is a cat. — Follows. “No cat is a dog” read the other way round is “no dog is a cat”; a “No” statement can be reversed.