RRB Group D · Bite-size lessons

Syllogism

About 8 min · General Intelligence and Reasoning · English

Time worked out from the lesson's 642 words at 150 words a minute, plus a minute for each question.

Syllogism is a critical reasoning topic in the Railway Group D exam where you draw logical conclusions from two or three given statements using quantifiers like "All," "Some" or "No." Each question typically gives 2–3 statements about categories (e.g., "All books are pens" and "Some pens are pencils") followed by 2–4 possible conclusions. Your job is to determine which conclusion(s) logically follow from the given statements — regardless of whether they match real-world facts.

Key ideas

• Quantifiers: The words "All," "Some" and "No" define the relationship between two categories. "All A are B" means every member of A is also in B. "Some A are B" means at least one A is B (possibly more, possibly all). "No A are B" means A and B have zero overlap.
• Subject and Predicate: In "All cats are animals," "cats" is the subject and "animals" is the predicate. The logical rules depend on whether terms are distributed (cover the entire category) or undistributed. "All" distributes the subject; "No" distributes both; "Some" distributes neither.
• Venn Diagram Method: Draw overlapping circles for each category. Shade or mark regions according to the statements, then check if the conclusion's diagram must be true based on your sketch. This visual method is foolproof for two-statement problems.
• Complementary Pairs: Two conclusions can form a complementary pair if exactly one must be true when neither can be proven individually. The standard pairs are: (1) "Some A are B" and "No A are B," and (2) "Some A are not B" and "All A are B." If statements allow both possibilities, mark "Either I or II follows."
• Possibility vs. Definiteness: A conclusion follows only if it is definitely true in every scenario allowed by the statements. If a conclusion is possible but not certain, it does not follow. For example, from "All A are B" and "All B are C," you can conclude "All A are C" (definite), but you cannot conclude "All C are A" (possible but not certain);

Watch out for

• Using real-world logic instead of formal logic: Students reject "All pens are chairs" because it seems absurd. → Always treat statements as true within the exercise, no matter how unrealistic.
• Confusing "possible" with "definite": A conclusion that might be true is not the same as one that must be true. → Mark a conclusion as following only if every allowed Venn diagram scenario supports it.
• Forgetting to check complementary pairs: When both conclusions seem false individually, students pick "Neither follows" without checking if they form a complementary pair. → Always test the two standard pairs if no individual conclusion is valid.

Quick reference

• All A are B: A entirely inside B; A distributed, B undistributed.
• No A are B: A and B separate; both distributed.
• Some A are B: A and B overlap; neither distributed; converts to "Some B are A."
• Complementary pairs: "Some/No" and "Some not/All" — if neither proven, check if exactly one must be true.
• Chain deduction: "All A→B" + "All B→C" gives "All A→C"; "Some" in chain usually yields no definite conclusion.

Check yourself: 3 questions

This lesson is cut from the topic's note, not rewritten. Fact-checked on 21 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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