Based only on the truth of the statement 'Some humans are intelligent', which one of the following options can be logically inferred with certainty? A. No human is intelligent. B. All humans are intelligent. C. Some non-humans are intelligent. D. Some intelligent beings are humans.

GATE 2023 · General Aptitude · Statements Follow · medium

Answer: D. Some intelligent beings are humans.

1. Formalize the given statement: Given: Some humans are intelligent. In first-order logic: exists x (human(x) and intelligent(x)). Call this witnessing individual 'p' — p is human and p is intelligent.
2. Check option A: No human is intelligent: Option A says: forall x (human(x) -> not intelligent(x)). But the given statement provides a counterexample p who is both human and intelligent. Option A is FALSE.
3. Check option B: All humans are intelligent: Option B is a stronger claim (universal) than the given (existential). 'Some' does not imply 'all'. We have no information about humans who might not be intelligent. Option B CANNOT be inferred with certainty.
4. Check option C: Some non-humans are intelligent: The given statement is about humans only; it provides no information about non-humans. We cannot infer anything about non-humans from a statement about humans. Option C CANNOT be inferred with certainty.
5. Confirm option D: Some intelligent beings are humans: From the formalized statement: exists x (human(x) and intelligent(x)). The same x satisfies: intelligent(x) and human(x). Therefore: some intelligent beings are humans. Option D follows with certainty by the symmetry of conjunction.