UPSC Prelims 2020·CSAT·Logical Reasoning·Deductive Logic

Two Statements are given followed by two Conclusions: Statements: All cats are dogs. All cats are black. Conclusion- I: All dogs are black. Conclusion- II: Some dogs are not black. Which of the above Conclusions logically follows/follow from the two given Statements disregarding commonly known facts?

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  1. AOnly Conclusion-I
  2. B(b) Only Conclusion-II
  3. C(c) Neither Conclusion-I nor conclusion-IICorrect
  4. D(d) Both Conclusions-I and Conclusion-II

Explanation

The statements tell us two things: 1. All cats are dogs. This means the set of cats is entirely contained within the set of dogs. 2. All cats are black. This means the set of cats is entirely contained within the set of black things. From these, we know that the dogs that are cats are black. However, we have no information about the dogs that are NOT cats. Let's analyze the conclusions: Conclusion I: All dogs are black. This does not logically follow. While all dogs that are cats are black, there might be other dogs (that are not cats) which could be any color (e.g., white, brown). The statements do not provide any information about these non-cat dogs, so we cannot conclude that all dogs are black. Conclusion II: Some dogs are not black. This also does not logically follow. It is entirely possible that ALL dogs (including those that are not cats) are black. The statements do not give us any information that would force some dogs to be non-black. We only know that the cat-dogs are black. Since neither Conclusion I nor Conclusion II can be definitively proven true based solely on the given statements, neither logically follows. The final answer is C.
Logical Reasoning: Two Statements are given followed by two Conclusions: Statements: All cats are dogs. All cats are black. Conclusion- I

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