Deduction guide
Deduction questions ask what must be true given the premises — syllogisms, conditional chains and quantifier logic. The answer is what the premises force, never merely what they make possible.
The method
- Ask what must follow, not what could be true.
- Use the contrapositive: 'if P then Q' also gives you 'if not Q then not P'.
- Draw quantifier statements ('all', 'some', 'none') as overlapping sets.
- For ordering relations, lay the items on a line and read off what is fixed.
Syllogism questions in aptitude tests
A reasoning syllogism gives you two or more premises and asks what must follow. Treat category words as sets and ignore whether the statements sound realistic. For example:
All analysts are graduates. No graduates are interns.
Conclusion: No analysts are interns.
The conclusion follows because the entire analyst set sits inside graduates, while the graduate and intern sets cannot overlap. Syllogism aptitude questions reward this strict set logic—not assumptions about the people described.
Common mistakes
- The converse error — reading 'if P then Q' as 'if Q then P'.
- Reading 'some' as 'most' or 'all'.
- Existential-import slips — assuming a category has members when it needn't.
- Flipping the direction of an ordering relation.
Worked example
A real question from this category, with the verified answer and the exact evidence that decides it.
Every chilled churn is moved to the loading bay. Every churn in the loading bay is weighed by the dairyman.
Conclusion: Every chilled churn is weighed by the dairyman. Does the conclusion follow from the premises?
Verified answer: A — Follows
The evidence
Every chilled churn is moved to the loading bay. Every churn in the loading bay is weighed by the dairyman.
The highlighted text decides the answer.
What to notice
Two one-way rules chain through 'the loading bay'.
The rule
Hypothetical syllogism: (chilled -> bay), (bay -> weighed) gives (chilled -> weighed).
Why the others are wrong
- B — Does Not Follow: The two rules chain cleanly; rejecting the link drops premise 2.
Frequently asked questions
What's the single most useful move?
The contrapositive. It is always valid and it rescues most conditional-chain questions where the converse would trap you.