Syllogism — Chaining several “some” statements across different sets Statements: • Some pens are pencils. • Some pencils are erasers. • Some erasers are sharpeners. Conclusions: I) Some sharpeners are pens. II) Some pencils are sharpeners. III) Some erasers are pens. Pick the conclusion(s) that necessarily follow.

Difficulty: Medium

Correct Answer: None follows

Explanation:


Introduction / Context:
This is a classic trap: several existential (“some”) premises are given, each possibly about different elements of the sets. The test is whether you can resist “connecting the dots” without a premise that forces the same individuals to serve in each overlap.


Given Data / Assumptions:

  • Some Pens ∩ Pencils ≠ ∅.
  • Some Pencils ∩ Erasers ≠ ∅.
  • Some Erasers ∩ Sharpeners ≠ ∅.


Concept / Approach:
From “some A are B” and “some B are C,” you cannot infer “some A are C” unless there is information that ties the same members across the overlaps. Each “some” could refer to a different subset of B. Thus, none of the cross-bridge conclusions is forced.


Step-by-Step Solution:

Step 1: Consider P1 ∈ Pens ∩ Pencils. This shows at least one pen-pencil exists.Step 2: Consider P2 ∈ Pencils ∩ Erasers, possibly P2 ≠ P1.Step 3: Consider E1 ∈ Erasers ∩ Sharpeners, possibly E1 ≠ P2.Step 4: None of these require an element in Pens ∩ Sharpeners, or in Pencils ∩ Sharpeners, or in Pens ∩ Erasers; each conclusion I–III could be false while all premises remain true.


Verification / Alternative check:
Create a model where the overlaps are pairwise disjoint: one item is a pen-pencil only, a second is a pencil-eraser only, and a third is an eraser-sharpener only. All premises hold, but none of I–III is satisfied, proving that no listed conclusion is necessary.


Why Other Options Are Wrong:

  • Only II or only III follow: neither is forced, because the critical overlaps can be on different members.
  • All follow: far too strong; there is no transitive law for “some.”


Common Pitfalls:
Illicitly chaining existential statements as if they were universal inclusions; forgetting that “some” can refer to different elements in each premise.


Final Answer:
None follows.

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