Syllogism — Aeroplanes, trains, chairs (watch existential import): Statements: 1. All aeroplanes are trains. 2. Some trains are chairs. Conclusions: I. Some aeroplanes are chairs. II. Some chairs are aeroplanes. III. Some chairs are trains. IV. Some trains are aeroplanes.

Introduction / Context:
This item combines a universal subset with a separate existential statement. Many exam keys assume classes referenced by universals are non-empty unless declared impossible; we adopt that common convention to align with the options.

Given Data / Assumptions:

• Aeroplane ⊆ Train (and assume ∃ Aeroplane).
• ∃ (Train ∩ Chair).

Concept / Approach:
From (2) we immediately get III “Some chairs are trains.” From (1) plus assumed non-emptiness of the Aeroplane class, we also have ∃ Aeroplane and hence ∃ (Train ∩ Aeroplane) → IV “Some trains are aeroplanes.” The cross-over conclusions I and II are not forced because the trains that are chairs need not be the aeroplane-trains.

Step-by-Step:
1) Use (2) to assert Chair ∩ Train is non-empty → III.2) From (1) with existence, pick an aeroplane; it is a train → IV.3) There is no requirement that any train-chair is also an aeroplane; hence I and II are not necessary.

Final Answer:
Only Conclusions III and IV follow.