UPSC Prelims 2001 Q149: Science & Technology – Logical Reasoning & Puzzles
Anand must be a vegetarian because he is a Buddhist. The argument assumes that
- (a) most Buddhists are vegetarians
- (b) all Buddhists are vegetarians
- (c) only Buddhists are vegetarians
- (d) most vegetarians are Buddhists
Answer: (b) all Buddhists are vegetarians
Explanation
Assumption behind 'Anand must be a vegetarian because he is a Buddhist'
| Option | Does the conclusion need it? |
|---|---|
| All Buddhists are vegetarians | Yes — only then must every Buddhist, including Anand, be a vegetarian |
| Most Buddhists are vegetarians | No — would only make it likely, not certain ('must') |
| Only Buddhists are vegetarians | No — says nothing about whether Buddhists are vegetarian |
| Most vegetarians are Buddhists | No — runs the wrong way |
The word 'must' makes the conclusion certain. That is valid only if every Buddhist is a vegetarian. 'Most' would allow Anand to be an exception, and the other two options reverse the direction of the link.
Answer: (b) all Buddhists are vegetarians.
Why each option is right or wrong
- (a) Incorrect. 'Most' would make Anand probably, not necessarily, vegetarian.
- (b) CORRECT. Only 'all Buddhists are vegetarians' supports 'must'.
- (c) Incorrect. 'Only Buddhists are vegetarians' does not make Buddhists vegetarian.
- (d) Incorrect. This runs from vegetarians to Buddhists, the wrong direction.
Key point
Syllogism: All Buddhists are vegetarians; Anand is a Buddhist; so Anand is a vegetarian.
Remember
'Must' needs 'all Buddhists are vegetarians'.
Common mistakes
- Choosing 'most' because it sounds more realistic.
- Reversing the link ('only Buddhists').
- Ignoring the certainty of the word 'must'.
Exam tip
A 'must' conclusion needs an 'all' premise.
Sources
- R. S. Aggarwal — A Modern Approach to Verbal Reasoning, chapter 'Statement and Assumptions'
- Irving M. Copi — Introduction to Logic, chapter on categorical syllogisms