Syllogism — RRB NTPC Reasoning
This topic carries roughly 8% of General Intelligence & Reasoning's 30 questions. The single most important discipline: judge a conclusion only by whether it must be true given the statements, never by whether it sounds true or false in the real world.
1. What RRB NTPC actually asks
Expect two (occasionally three) statements using All/No/Some/Some-not, followed by one or two conclusions, and the requirement to judge whether each conclusion follows definitely from the statements.
2. The four statement types
| Type | Form | Venn picture |
|---|---|---|
| A (Universal affirmative) | All S are P | S entirely inside P |
| E (Universal negative) | No S are P | S and P completely separate |
| I (Particular affirmative) | Some S are P | S and P overlap (at least partially) |
| O (Particular negative) | Some S are not P | at least part of S is outside P |
3. The Venn diagram method
For each pair of statements, draw every Venn diagram arrangement consistent with BOTH statements. A conclusion is valid only if it holds true in every single one of those consistent arrangements — if even one valid arrangement breaks the conclusion, it does not follow.
4. The two classic invalid patterns
"All + Some" does not chain to "Some." All cats are animals; some animals are wild — this does NOT mean some cats are wild, because the "wild" animals mentioned might be entirely outside the cat group.
"Some + Some" never yields a definite conclusion. Some students are athletes; some athletes are tall — this does NOT mean some students are tall, because the "tall" athletes and the "student" athletes might be two completely different, non-overlapping subsets of athletes.
Worked examples
Q1. Statements: All roses are flowers. All flowers need water. Conclusion: All roses need water.
Pick an option to check your answer.
Show explanation
Solution. This is a valid A-A-A chain: All roses are flowers (roses entirely inside flowers), all flowers need water (flowers entirely inside "need water"). Since roses are entirely inside flowers, and flowers are entirely inside "need water," roses must be entirely inside "need water" too — there is no possible Venn arrangement satisfying both statements where this fails. Answer: (a).
Q2. Statements: All cats are animals. Some animals are wild. Conclusion: Some cats are wild.
Pick an option to check your answer.
Show explanation
Solution. This is the classic "All + Some" trap. All cats are animals places cats entirely inside animals, but "some animals are wild" only guarantees that SOME part of the larger animal circle overlaps with "wild" — that overlapping part could be entirely outside the cats subset.
Draw it: animals is a large circle, cats is a smaller circle inside it, and "wild" could overlap animals in a region that doesn't touch cats at all. Since a valid arrangement exists where the conclusion fails, it does not follow. Answer: (b).
6. Common traps
- Judging a conclusion by real-world truth instead of logical necessity. A syllogism conclusion must follow from the STATEMENTS given, even if the statements themselves are factually odd or unusual.
- Chaining "All" and "Some" statements as if they combine like "All." All+Some never guarantees a "Some" conclusion connecting the outer terms — always check for a valid counter-arrangement.
- Assuming two "Some" statements combine to a definite conclusion. Some+Some never yields a certain conclusion about the two outer terms, since the "some" portions might not overlap with each other.
- Missing that "No" statements are symmetric. "No A are B" is logically identical to "No B are A" — this can simplify conclusion-checking.
7. Guessing strategy
Recognising the "All+Some" and "Some+Some" invalid patterns immediately, without drawing a diagram, resolves a large fraction of syllogism questions in seconds — reserve the full Venn-diagram method for statement combinations that don't match these two recognisable traps.
Summary
- Syllogism is roughly 8% of General Intelligence & Reasoning's 30 CBT 1 questions.
- Judge conclusions purely on logical necessity from the given statements, never on real-world plausibility.
- The four statement types: All (A), No (E), Some (I), Some-not (O), each with a specific Venn diagram picture.
- A conclusion is valid only if it holds in EVERY Venn arrangement consistent with both statements.
- "All + Some" never yields a "Some" conclusion connecting the outer terms — a classic, deliberately planted trap.
- "Some + Some" never yields any definite conclusion about the outer terms.
