🔎 TNPSC Group IV | Day 18 — Logical Reasoning: Foundations 30 October 2026 | Friday | 4:00 PM IST Category: TNPSC Grp IV | Aptitude & Mental Ability — Reasoning
1. What Is Logical Reasoning? Logical reasoning means using the statements and relationships given in a question to identify conclusions that must follow. A conclusion that sounds reasonable is not necessarily proved. In examination questions, use the supplied premises rather than importing outside assumptions.
2. Essential Terms • Statement: Information that the question asks you to accept as given. • Conclusion: An idea derived logically from the statements. • Assumption: A condition taken for granted but not directly stated. • Necessary conclusion: True in every situation consistent with the statements. • Possible conclusion: May be true in some situations but is not guaranteed. • Contradiction: A claim incompatible with the given statements.
3. Core Rules Rule 1 — If all A are B and all B are C, then all A are C. This conclusion is certain. Rule 2 — From “All A are B,” you cannot conclude “All B are A.” Rule 3 — From “Some A are B,” you cannot conclude “All A are B.” Rule 4 — “If P, then Q” means P ⇒ Q. When P is true, Q follows. But Q being true does not prove that P occurred. Rule 5 — If P ⇒ Q, then “not Q ⇒ not P” is also valid. This is called the contrapositive. Rule 6 — For ranking questions, combine comparisons into one chain using > or <. Never invent an unstated comparison.
4. Fast Solving Method (1) Identify whether the question asks what MUST follow or what MAY be possible. (2) Replace long statements with short symbols such as A, B, C or P, Q. (3) Watch the words “all,” “some,” “none” and “only.” (4) Convert comparisons into arrows, sets or a simple diagram. (5) One counterexample is enough to disprove a claimed necessary conclusion. (6) Do not assume a relationship that the question never gives.
5. Fully Worked Examples
Example 1 — Classification and Necessary Conclusion Statement 1: All teachers are graduates. Statement 2: All graduates are literate. Question: Are all teachers literate? Solution: Teachers ⊆ Graduates; Graduates ⊆ Literate people. Therefore Teachers ⊆ Literate people. Answer: Yes. It necessarily follows. Important: This does NOT establish that every literate person is a teacher.
Example 2 — Conditional Reasoning Statement: If the alarm sounds, the guard wakes up. Case A: The alarm sounds. Does the guard wake up? Solution: P ⇒ Q, and P is true. Therefore Q follows. Answer: Yes. Case B: The guard wakes up. Must the alarm have sounded? Solution: No. The guard could have woken up for another reason. Case C: The guard did not wake up. Could the alarm have sounded? Solution: If the stated rule is true, the alarm did not sound. This is the contrapositive.
Example 3 — Height Ranking Kavi is taller than Bala. Bala is taller than Devi. Devi is taller than Arun. Who is tallest and who is shortest? Solution: Kavi > Bala > Devi > Arun. Tallest: Kavi. Shortest: Arun. Shortcut: Write every comparison in a single > chain.
Example 4 — Direction and Distance A person walks 6 metres north and then 8 metres east. In which direction and how far is the person from the starting point? Solution: North followed by east gives a final position to the northeast. Straight-line distance = √(6² + 8²) = √(36+64) = √100 = 10 metres. Answer: 10 metres to the northeast. Important: The total distance walked is 6+8 = 14 metres, while the straight-line displacement is 10 metres.
Example 5 — Limits of “Some” Statement 1: All mangoes are fruits. Statement 2: Some fruits are yellow. Question: Must some mangoes be yellow? Solution: No. The yellow fruits could all be fruits other than mangoes. Both statements can be true while the proposed conclusion is false. Answer: The conclusion does not necessarily follow.
6. Examination Shortcuts • Never reverse “All A are B” into “All B are A.” • For “If P, then Q,” Q alone does not prove P. • “Some” means at least one; it does not mean “all.” • Combine height, age and marks comparisons into one ordered chain. • Distinguish total walking distance from straight-line distance. • “Cannot be determined from the information given” can be the correct answer.
7. Textbook and PYQ Evidence The official TNPSC Group IV SSLC syllabus, Code 496, places Logical Reasoning in Part B, Unit II — Reasoning (10 questions), alongside Puzzles, Dice, Visual Reasoning, Alpha Numeric Reasoning and Number Series. Related government textbook: Class 6 Mathematics, Term III, Unit 5 — Information Processing (2018 first edition), Exercises 5.1 and 5.2. The original textbook PDF shows main question numbers 1–15 in Exercise 5.1 and 1–13 in Exercise 5.2; subquestions must be counted separately. Relevant items identified: Exercise 5.2, Q5 (letter–number coding), Q7 (coded message) and Q8 (relationships/ordering). Their presence in the 2018 edition is verified. The 2026–27 edition has not yet been compared. Book-back questions completed in this lesson: 0. Reserved for an evening practice batch: 3 main questions. The full count of syllabus-relevant subquestions across the chapter is still pending. Verified TNPSC Group IV PYQs for this topic: 0. An inventory of the user's 18 PDFs was located, but question numbers and answers have not yet been matched with an official final answer key. All five worked examples above are original instructional models, not textbook book-back questions or TNPSC PYQs.
8. Spaced Revision 31 October (+1 day); 2 November (+3 days); 6 November (+7 days); 13 November (+14 days). Also revise yesterday's Compound Interest lesson today (+1 day), as a separate short revision activity.
9. Push Notification Title: 🧠 TNPSC Group IV | Day 18 — Logical Reasoning! Message: Learn statements and conclusions, all/some rules, conditional logic, rankings and directions through five fully worked bilingual examples on ETN News.
SOURCE REGISTER / ஆதாரங்கள் 1. Official TNPSC Group IV SSLC syllabus Code 496, Part B Unit II: https://tnpsc.gov.in/static_pdf/syllabus/496_Group%20IV%20Syllabus.pdf 2. Government of Tamil Nadu, Class 6 Mathematics Term III Volume 2 (2018 first edition), Chapter 5 pp. 81–84 (PDF pages 86–89), Exercises 5.1 and 5.2, mirrored copy of original textbook: https://cdn1.byjus.com/wp-content/uploads/2019/07/Tamil-Nadu-Class-6-Maths-Book-Term-3English.pdf 3. State Council of Educational Research and Training: https://scert.tnschools.gov.in/ SOURCE CAUTION: 2018 textbook edition verified; 2026–27 edition source not yet verified. PYQ question-level source not yet verified. Do not claim the full book-back chapter is completed. PUBLICATION: Prepared only; no automatic ETN posting or push notification.
