Introduction

The person who started documenting and deductive reasoning long ago and in the fourth century BC was a Greek philosopher called Aristotle. Deductive reasoning deals with truth and logic; hence it is also called deductive logic or top down logic. Deductive reasoning involves gradually collecting all the logical facts from the premises and narrowing them down until a logical conclusion is made.

The applications of deductive reasoning are less in real life. Deductive reasoning is widely used in fields related to math. Otherwise, all our ideas are generalized and thus belong to the category of inductive reasoning. Inductive reasoning is also called bottom up logic. 

Reasoning

Logic and reason both terms can be used interchangeably, and hence deductive reasoning and deductive logic are the same things. 

Now, reason can be categorized as follows:

• Subjective Reasons
• Objective Reasons

• Subjective Reasons

These kinds of reasons depend upon personal opinions, preferences and judgments. These can differ individually. It may be true and may not be true for someone. 

Example: Yeats is the greatest poet of all time. 

• Objective Reasons

Objective reasons are universally accepted as these are independent, true, and factual. It’s the same for everyone. Usually, deductive reasoning involves objective reasons. 

Example: Apple falls to the ground because of gravity.

What is Deductive Reasoning?

Deductive reasoning refers to concluding or extrapolating the facts to get a specific outcome. This reasoning is also known as Syllogisms. 

Deductive reasoning mainly consists of three parts: 

• First premise
• Second premise 
• Conclusion (Conjecture)

The official term for two or more sentences from which a logical conclusion is drawn is called a premise. Premises are usually true in nature and hold factual information. A conclusion can also be called as a conjecture which refers to observations or guesses drawn from known facts. Premises and conclusions combined are known as an argument.

In Deductive reasoning, the argument has another name which is known as a valid argument. A valid argument also refers to logically necessary. In logical reasoning, the content doesn’t matter but the method. Deductive reasoning’s conclusion is always true as the conclusion necessarily follows the stated facts and becomes a logically necessary fact.

The visual representation of deductive reasoning looks like the shape “V” as you deduce the facts to reach a very specific conclusion. The invalid argument, however, consists of logically possible or logically impossible scenarios. And valid argument refers to inductive reasoning/logic. 

Note: answers for deductive reasoning would always be logically necessary, with the conclusion having very close proximity with logic and facts. 

Deductive Reasoning Examples:

Example 1

Premise 1: All girls are mortal. 

Premise 2: Myra is a girl. 

Conclusion: Myra is Mortal. 

Example 2

Premise 1: The chocolate costs 70₹. 

Premise 2: He has 100₹. 

Conclusion: He can buy chocolates. 

Example 3:

Premise 1: Snake poison is dangerous. 

Premise 2: The forest has snakes. 

Conclusion: Going to the forest is dangerous. 

Deductive Reasoning vs. Inductive Reasoning:

The two main and popular types of reasoning are deductive and inductive.

Following are the differences between these two types of reasoning:

Conclusion

Deductive reasoning is less used in real life. The applications of deductive reasoning imply upon science and mathematics vastly and mainly. However, it is not possible that all the premises mentioned or available are always true facts, and hence inductive reasoning is used more than deductive reasoning in real life. The phenomenon of making assumptions is what leads to great discoveries, so even if deductive reasoning helps to know facts, inductive reasoning is what leads to fundamental ideas leading to unknown facts. If we talk about science and mathematics with reference to deductive reasoning, Math is more prone to be factual than science as new discoveries can change the scientific conclusions.