Fact 1: Humans are mammals.
Fact 2: Some humans are engineers.
Fact 3: Engineers build houses.
If the above statements are facts, which of the following can be logically inferred?
I. All mammals build houses.
II. Engineers are mammals.
III. Some humans are not engineers.
Options:
(A) II only.
(B) III only.
(C) I, II and III.
(D) I only.
Official Answer Key:
A
Step-by-Step Solution & Explanation
• Fact 1 establishes: $\text{Humans} \subset \text{Mammals}$.
• Fact 2 establishes: Engineers under consideration are human. Since all humans are mammals, those who are engineers are necessarily mammals (Inference II is valid).
• Evaluating I: Only engineers build houses; not all mammals build houses (I is invalid).
• Evaluating III: In formal deductive logic, “some A are B” confirms the existence of at least one A that is B, but does not strictly guarantee that some A are NOT B without additional premises (III is not deductively certain).
• Therefore, only II can be logically inferred.
• Final Answer: (A) II only.
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