Reasoning Syllogism Rules
Quick Revision Sheet: Syllogism Rules for RRB
Key Concepts
- Syllogism: Statement + Statement ⇒ Conclusion (2 Premises → 1 Conclusion)
- Proposition: Subject + Predicate (e.g., All A are B)
- Standard Format: Always write as Subject → Predicate
- 3 Terms Only: Major, Minor, Middle (Middle term must appear in both premises)
5 Standard Propositions & Their Codes
| Proposition |
Code |
Distribution |
| All A are B |
A |
Subject only |
| No A are B |
E |
Both terms |
| Some A are B |
I |
None |
| Some A are not B |
O |
Predicate only |
Golden Rules (Must Remember)
- A + A ⇒ A (All+All → All)
- A + E ⇒ E (All+No → No)
- E + A ⇒ O* (No+All → Some-not, reversed)
- E + I ⇒ O* (No+Some → Some-not, reversed)
- I + A ⇒ I (Some+All → Some)
- No Conclusion Combo: A + O, E + O, I + O, O + any
Shortcut Tricks
- Venn-Draw in 5 sec: Draw 3 overlapping circles, shade as per statement
- Reversal Trick: Swap Subject-Predicate if needed to match standard code
- Complementary Pair: If “Some” & “No” both appear → Either-or choice
- Possibility ≠ Conclusion: “Can be” questions are always wrong if definite conclusion exists
Mnemonics
- AEIOU → Remember code order: A-E-I-O (U for Universal statements)
- “No OO” → O-type with O-type gives No Conclusion
- “All Eagles Eat” → A+E ⇒ E (All+No → No)
Quick Facts Table
| Fact |
Reminder |
| Middle term must be distributed once |
Check code table |
| Conclusion can’t have middle term |
Strike it out |
| “Some not” reversed in E+I, E+A |
Flip subject-predicate |
| Only 6 valid combos |
Memorise A+A, A+E, E+A, E+I, I+A, I+I |
| Either-or pair |
One positive, one negative; same subject & predicate |
Common Exam Q&A
Q1: All pens are pencils. No pencil is rubber. Conclusion?
Answer: No pen is rubber. (A + E ⇒ E)
Q2: Some cats are dogs. All dogs are rats. Conclusion?
Answer: Some cats are rats. (I + A ⇒ I)
Q3: No apple is mango. Some mango is orange. Conclusion?
Answer: Some orange is not apple. (E + I ⇒ O, reversed)
Last-Day Checklist
BETA
