Syllogism
About 7 min · General Intelligence and Reasoning · English
Time worked out from the lesson's 498 words at 150 words a minute, plus a minute for each question.
Syllogism tests your ability to draw valid logical conclusions from two or more statements without relying on general knowledge or assumptions. In RRB NTPC, you will encounter 2–3 statement syllogisms using quantifiers like "All," "Some," and "No." Each problem provides premises (statements) and asks whether given conclusions logically follow.
Key ideas
- Universal Affirmative (All A are B): Every member of set A is contained within set B. Venn diagram shows circle A completely inside circle B.
- Universal Negative (No A are B): Sets A and B have no common members. Venn diagram shows two separate, non-overlapping circles.
- Particular Affirmative (Some A are B): At least one member of A is also a member of B. Venn diagram shows overlapping circles with intersection marked; "some" means "at least one," not "only a few."
- Particular Negative (Some A are not B): At least one member of A is outside B. Part of circle A extends beyond circle B.
- Complementary pairs: "All A are B" and "Some A are not B" cannot both be true. "No A are B" and "Some A are B" cannot both be true. These help in either-or conclusion questions.
Watch out for
- Applying real-world knowledge → Ignore what you know about the actual world: If the statement says "All tables are chairs," accept it as true for the problem even though it contradicts reality. Base conclusions only on given statements.
- Misunderstanding "some" as "only some" or "a few" → "Some" means "at least one": "Some A are B" does not exclude the possibility that all A are B. It simply confirms at least one overlap.
- Assuming "All A are B" means "All B are A" → Converse is not automatic: The statement "All mangoes are fruits" does not imply "All fruits are mangoes." Never reverse a universal affirmative unless explicitly stated.
Quick reference
- Use Venn diagrams for every problem — visual method eliminates errors.
- "All A are B" = A circle inside B circle.
- "No A are B" = A and B circles completely separate.
- "Some A are B" = A and B circles overlap; at least one element in intersection.
- Two "some" statements or two "no" statements → no valid conclusion.
Check yourself: 3 questions
1. Statements: All books are notebooks. All notebooks are papers. Conclusions: I. All books are papers. II. Some papers are books. Which conclusion(s) logically follow(s)?
2. Statements: Some doctors are engineers. No engineer is a lawyer. Conclusions: I. Some doctors are not lawyers. II. No doctor is a lawyer. Which conclusion(s) logically follow(s)?
3. Statements: All trains are vehicles. Some vehicles are buses. No bus is a car. Conclusions: I. Some trains are buses. II. No train is a car. Which conclusion(s) logically follow(s)?
This lesson is cut from the topic's note, not rewritten. Fact-checked on 18 Oct 2026: an AI-assisted check of this note against cited sources; the errors it found were corrected that day. Some errors may remain. The questions are from Shishya's validated question bank.
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