Logical fallacy check in syllogism: from 'All boys are honest' and 'Sachin is honest', decide whether it necessarily follows that Sachin is a boy or that all honest persons are boys

Given data

• Premise 1: All boys are honest (Boys ⊆ Honest).
• Premise 2: Sachin is honest.
• Conclusions: (I) Sachin is a boy. (II) All honest persons are boys.

Concept/Approach (why this method)

Recognize the affirming the consequent fallacy: from 'All boys are honest' and 'Sachin is honest', you cannot infer Sachin is a boy; many non-boys can be honest too.

Step-by-Step calculation (logical derivation)1) Premise 1 gives a one-way inclusion: Boys ⊆ Honest.2) Premise 2 locates Sachin in Honest, but does not place him inside Boys.3) Conclusion I requires Honest ⊆ Boys for Sachin, which we do not have.4) Conclusion II asserts Honest ⊆ Boys, the converse of Premise 1, which is not given.

Verification/Alternative

Counterexample: A girl can be honest without being a boy; thus both conclusions fail.

Common pitfalls

• Reversing subset relations.
• Forgetting that 'All A are B' does not imply 'All B are A'.

Final AnswerNeither I nor II follows.