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Particular conversion and scope of a universal negative: from ‘‘Some desks are caps’’ and ‘‘No cap is red’’ decide which conclusions about caps being desks and desks being non red are compelled.

Difficulty: Medium

Correct Answer: Only conclusion I follows

Explanation:

Work each conclusion directly from the premises.

  • Premise 1: Some desks are caps, so Desks ∩ Caps ≠ ∅.
  • Premise 2: No cap is red, so Caps ∩ Red = ∅.
  • Conclusions: I. Some caps are desks. II. No desk is red.

Concept/Approach
Particular statements convert, while universal negatives do not automatically extend to supersets.
Testing conclusion I
From Some desks are caps we can convert to Some caps are desks. Hence I follows.
Testing conclusion II
Only caps are known to be non red. Desks that are not caps might still be red. Thus II is not guaranteed.
Verification/Alternative
Model: Caps = {a}, Desks = {a, d2}, Red = {d2}. Premises hold; I true, II false.
Common pitfalls
Extending a restriction on a subset to the entire superset.
Final Answer
Only conclusion I follows.
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