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Logical deduction is a process of reasoning where one derives a logically necessary conclusion from given premises. In other words, it involves drawing conclusions based on a set of statements or conditions that are provided. Logical deduction is a crucial skill in various competitive exams, including the Common Admission Test (CAT) for management education.

What is Logical Deduction?

  • Logical deduction is the process of drawing conclusions based on premises or statements that are known or assumed to be true. It involves using reasoning and logical principles to derive new information or insights.
  • The main purpose of logical deduction is to make valid and sound arguments and arrive at accurate conclusions. It helps us analyze and evaluate information, solve problems, and make informed decisions.

Logical Deductions | CSAT Preparation - UPSC

How does Logical Deduction Work?

  • Logical deduction operates on the principles of deductive logic. It starts with a set of premises or statements and applies logical rules to derive a conclusion. 
  • This process ensures that the conclusion is necessarily true if the premises are true.

Logical Deductions Premises - Various Patterns

Type 1: If A Happens B Happens

  • This means that A leads to B, but does not mean the reverse, i.e., if B has happened, A must have happened. In such situations, A is a sufficient condition for B, but is not a necessary condition.
  • Let’s look at the following example:
    If I go to a movie, I enjoy myself.
    ~ This would mean, that if I have gone to the movie, I will definitely enjoy myself. However, it does not mean that if I have enjoyed myself, I must have gone to the movie—there are so many ways of enjoying yourself.
    Another example of this type would be:
    If Amir acts in a movie, he will earn money.
    ~This does not mean that if he has earned money, he must have acted in a movie.

Type 2: Only If A Happens B Happens

  • In this case, A is a necessary and sufficient condition for the occurrence of B. In this case, there is reversibility of the logic, i.e., if B has happened, A must have happened.
  • Example:
    Only if Saurav plays the match, will he get a hundred.
    ~ If Saurav has got a hundred, he must have played the match.

Type 3: If A Happens B Does Not Happen

  • In this case, if A has happened, B does not happen. The opposite is also true, i.e., if B has happened, A must not have happened.
  • Example:
    If Martina plays well, Sania will not win.

Type 4: If A does not Happen B will Happen

  • Again in this case, the reverse might not be true.
  • Example:
    If Anand does not come, Kasparov will. This does not mean that if Kasparov comes, Anand will not come.

Type 5: Either A or B will Happen

  • One of the two has to happen. At the same time, the two events are exclusive of one another. If one happens, the other will not happen.
  • Example:
    Either he becomes a TV star or he becomes a movie star.

Solved Examples

Example 1: Shahrukh either acts as a villain, or he acts as a hero.
A. Shahrukh acts like a hero.
B. Shahrukh does not act like a villain.
C. Shahrukh acts like a villain.
D. Shahrukh does not act like a hero.
(a) Only CD
(b) Only BA
(c) CD and BA
(d) None of these

This question is based on an EITHER-OR Premise. Thus, we can see that CD is correct. Since, if he acts like a villain—(Statement C) he will not act like a hero (Statement D). Similarly, BA can also be seen to be true. Hence option (c) is correct.

Question for Logical Deductions
Try yourself:Ravan gets a mild flu whenever he eats icecreams.
(A) Ravan gets a mild flu.
(B) Ravan does not eat icecreams
(C) Ravan does not get a mild flu.
(D) Ravan eats icecreams.
View Solution

Example 2: If I talk to my girl friends, then I do not need to take a pill for heartache.
A. I talked to my girl friends.
B. I did not need to take a pill for heartache.
C. I needed to take a pill for heartache.
D. I did not talk to my girl friends.
(a) Only AB
(b) Only DC
(c) Only CD
(d) AB and CD

This question falls under the category of if A happens, then B does not happen. However, if B has not happened, it does not mean that A has happened.
AB and CD are both logically correct.

Example 3: You can find Chinese toys only in China.

A. I didn't find Chinese toys.
B. I found Chinese toys.
C. I went to the fair.
D. I didn't go to China. 

(a) CD
(b) CB
(c) CA
(d) DA

Ans: (d) 

Example 4: Either the bus is late, or it has turned turtle.

A. The bus is late.
B. The bus is not late.
C. The bus has turned turtle.
D. The bus has not turned turtle.

(a) AB
(b) DB
(c) CA
(d) BC

Ans: (d) 

Example 5: You cannot clear the CAT unless you are intelligent.

A. You are intelligent.
B. You can clear the CAT.
C. You are not intelligent.
D. You cannot clear the CAT.

(a) BD
(b) AC
(c) CD
(d) AB

Ans: (c) 

The document Logical Deductions | CSAT Preparation - UPSC is a part of the UPSC Course CSAT Preparation.
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FAQs on Logical Deductions - CSAT Preparation - UPSC

1. What is logical deduction?
Logical deduction is a process in which conclusions are drawn based on logical reasoning from given premises or statements. It involves using logical rules and principles to infer new information or reach a valid conclusion.
2. How does logical deduction work?
Logical deduction works by analyzing the given premises or statements and applying logical rules to draw conclusions that are logically valid. It involves identifying patterns, making logical connections, and eliminating possibilities to arrive at the most reasonable and logical outcome.
3. What are the premises used in logical deduction?
The premises used in logical deduction are the given statements or facts that serve as the basis for drawing conclusions. These premises can vary in complexity and can be presented in various patterns such as conditional statements, syllogisms, or logical puzzles.
4. Can you provide some examples of logical deductions?
Certainly! Here are a few examples of logical deductions: Example 1: Premise 1: All cats are mammals. Premise 2: Fluffy is a cat. Conclusion: Therefore, Fluffy is a mammal. Example 2: Premise 1: If it rains, the ground gets wet. Premise 2: It is raining. Conclusion: Therefore, the ground is wet. Example 3: Premise 1: All birds have feathers. Premise 2: Penguins are birds. Conclusion: Therefore, penguins have feathers.
5. What are some frequently asked questions about logical deductions in the CAT exam?
Here are some frequently asked questions about logical deductions in the CAT exam: 1. How can I improve my logical deduction skills for the CAT exam? 2. What are the common types of logical deduction questions asked in the CAT exam? 3. Are there any specific strategies or techniques to solve logical deduction questions quickly? 4. Can logical deduction questions in the CAT exam be time-consuming? 5. Are there any recommended resources or practice materials to prepare for logical deduction in the CAT exam?
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