Deductive reasoning: characteristics and examples

Deductive reasoning helps us understand the world, solve problems, and optimize our learning. We tell you what it consists of.

Written and verified by the psychologist Elena Sanz on August 30, 2021.

Last update: August 30, 2021

To understand the world around us, streamline our thinking and optimize learning we need to make associations and categories. That is to say, we need to start from a valid knowledge that we already have and extrapolate it to other similar situations. This is deductive reasoning.

To deduce is to draw conclusions based on a general premise or principle. In other words, deductive reasoning leads us from a main law that we take to be true to the interpretation of other related situations.

It is, therefore, a reasoning from top to bottom, from the general to the precise. It is usually established from the age of 11, in the Piagetian stage of formal operations.

Types of deductive reasoning

In deductive reasoning always a particular conclusion is inferred from a general premise. The argument is divided into two complementary premises and a conclusion reached after the deduction process.

However, there are different ways in which this type of logical thinking can be applied. We will show them to you below.



Syllogism

The syllogism is the deductive reasoning par excellence. The notion of this type of thinking was introduced to science by Aristotle, which is why it is also known as Aristotelian syllogism. In this process, a major or universal premise, a minor or particular premise, and a conclusion derived from them are exposed.

Aristotle was the one who systematized deductive thinking to shape it in the sciences.

Modus putting ponies

This type of deductive reasoning is also called assertion of antecedent, since it is based on that the second premise confirms the conditional information of the first. That is, in the first part a condition is proposed and in the second it is confirmed. Thus, the scheme that follows is the following: if P implies Q, and if P is true, then Q is true.

Modus tollendo tollens

In this case, the first premise also exposes a condition, but in the second part this condition is not confirmed. This form of deductive reasoning is also known as consequent denial and the scheme that follows is the following: if P implies Q, and Q is not true, then P is not true either.



Characteristics of deductive reasoning

If with the above you still have doubts about what deductive reasoning is or how it works, below we will show you its main elements and characteristics. In this way, it will be easier for you to understand what it is.

Argument

The logical argument is the process or discourse that allows us to justify or refute the veracity Of something. That is, expose it as false or as true. This statement is made up of three assertions: two of them that act as premises and a third that is derived from the previous ones.

Thus, for a proposition to receive the role of premise it must be placed before the conclusion; and for a proposition to receive the role of conclusion, it is enough that it is in the last place. It is not the content of the propositions that determines their role, but the place they occupy within the argument.

The premises are always true

For deductive reasoning to exist, necessarily its premises have to be taken as true. These are laws, axioms or general principles that are always accepted as true, since they are the basis of the deduction process.

No new information

The conclusion follows from the premises, so it does not provide any new information. It only reaffirms, for a specific case, what the premises already assumed to be true in a general way.

The conclusions are considered valid by the form

Conclusions are necessarily admitted as valid, provided that the premises are true and the deduction process has been carried out well. That is, since they do not provide new information, their validity does not depend on the content (what they say), but on the fact that they have been reached after adequate deductive reasoning.

Can lead to fallacies

Deductive reasoning can lead to fallacies or conclusions that are not true or do not conform to reality. This happens if the deduction is made from doubtful or false premises, or if the reasoning is faulty.

Examples of deductive reasoning

Perhaps the above is somewhat complex to understand. Therefore, below we show you some examples that illustrate the process deductive reasoning. As you read them, you will surely discover that you use this type of thinking on a daily basis.

1. Syllogism

  • All living things are born and die (major premise).
  • Dogs are living things (minor premise).
  • Dogs are born and die (conclusion).

2. Modus putting ponies

  • If it rains, the street gets wet.
  • It's raining.
  • Then the street gets wet.
We use deductive thinking on a daily basis, so that everyday life is understood by this process.

3. Modus tollendo tollens

  • If there is sunlight, then it is daytime.
  • It's not daytime.
  • Therefore, there is no sunlight.

4. Fallacy based on false premises

  • All men have short hair.
  • Juan is a man.
  • Juan has short hair.

5. Fallacy based on a failure in the application of deductive reasoning

  • If it rains, the streets get wet.
  • The streets are wet.
  • So, it has rained.

Deductive reasoning is part of life from a young age

Deductive reasoning is one of the modes of thought that more we use to understand the world around us. It is also widely used within the investigative process, especially in sciences such as mathematics or physics. And although children reach it sooner or later, it can be interesting to help them promote it.

Managing logical thinking helps children to understand the world, to function in their environment, to optimize their learning and to solve problems more efficiently. Therefore, you can use resources such as chess or puzzles.

In this way, the child will learn to transfer knowledge and generalize their learning. You will be much more aware of how the environment works around you.