Syllogism
About 7 min · Reasoning Ability · English
Time worked out from the lesson's 476 words at 150 words a minute, plus a minute for each question.
Syllogism is a topic in IBPS PO Prelims Reasoning section. Unlike puzzles that can be time-consuming, syllogism questions follow fixed logical rules — once you master them, you can solve each question quickly.
Key ideas
- Universal Affirmative (A-type): "All A are B" — Every member of A belongs to B. A is completely inside B, but B may extend beyond A.
- Universal Negative (E-type): "No A is B" — There is zero overlap between A and B. The two circles never touch.
- Particular Affirmative (I-type): "Some A are B" — At least one A is B. There is partial overlap; could also mean all A are B (some includes all as a possibility).
- Particular Negative (O-type): "Some A are not B" — At least one A exists outside B. Part of A does not overlap with B.
- "Only A are B" = "All B are A" — This reversal is a common trap. "Only teachers are graduates" means all graduates are teachers, not the other way around.
Watch out for
- Treating "Some" as "Only Some" → "Some A are B" does NOT mean "Some A are not B." In logic, "some" includes the possibility of "all." Always check both scenarios.
- Confusing "Only" with "All" → "Only cats are pets" does NOT mean "All cats are pets." It means "All pets are cats." Draw the Venn diagram with pets inside cats.
- Forcing a conclusion from two particular statements → Two I-type statements (Some-Some) never give a definite conclusion. Don't guess — mark "no conclusion follows."
Quick reference
- All A are B → A sits completely inside B.
- No A is B → A and B circles never touch.
- Some A are B → Circles overlap; could overlap completely.
- Only A are B = All B are A — memorize this conversion.
- Two negative statements → No definite conclusion ever.
Check yourself: 3 questions
1. Statements: All books are pens. Some pens are pencils. Conclusions: I. Some books are pencils. II. Some pencils are books. III. Some pencils are pens. Which conclusion(s) logically follow(s) from the given statements?
2. Statements: All dogs are animals. No animal is a plant. All roses are plants. Conclusions: I. No dog is a plant. II. No rose is an animal. III. Some roses are animals. Which conclusion(s) logically follow(s) from the given statements?
3. Statements: Some doctors are engineers. All engineers are scientists. No scientist is a teacher. Conclusions: I. Some doctors are scientists. II. Some doctors are not teachers. III. No engineer is a teacher. Which conclusion(s) logically follow(s) from the given statements?
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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