Induction and deduction

Induction and deduction are forms of reasoning. Induction attempts to reach general conclusions from particular premises, while deduction relies on general premises to reach a particular conclusion.

DefinitionForm of reasoning that uses specific data to reach general conclusions.Form of reasoning that uses general data to reach specific conclusions.
  • Data collection.
  • Observation.
  • Pattern identification.
  • Conclusion.
  • Data collection.
  • Observation.
  • Conclusion.
  • Brings new knowledge.
  • If the premises are true, the conclusion will likely be true.
  • The conclusion is not in the premises.
  • It does not bring new knowledge.
  • If the premises are true, the conclusion is true.
  • The conclusion is in the premises.
  • Premise A : Earth is hemispherical.
  • Premise B : Earth is a planet.
  • Conclusion : All planets are hemispherical.
  • Premise A : the planets are hemispherical.
  • Premise B : Earth is a planet.
  • Conclusion : the Earth is hemispherical.

What is induction?

It is a form of reasoning that considers specific data analysis to infer general conclusions about the nature of the phenomenon studied. That is, it is a type of scientific reasoning that studies the particular to arrive at propositions that apply to all phenomena of the same category.

This type of reasoning is known as the inductive method and is applied following certain criteria.

Inductive method

To apply the inductive method, data of a series of phenomena of the same nature are observed and collected, in order to find a common principle to all of them. This being the case, it can be said that if a group of newborns cry when they are hungry, then it can be concluded that all newborns cry when they are hungry.

However, although induction is a widely used method, it is not without its flaws. In fact, in deductive reasoning there is no criterion to determine the validity of an argument, which has been called “the problem of induction.”

What is the problem of induction ? This is what happens in cases where the (general) conclusions do not correspond to the (particular) premises.

An example of the induction problem would be the following:

An isolated indigenous tribe has contact for the first time with a group of white-skinned explorers. Looking at them, they might conclude that outside their territory all people look like explorers. However, we know that this is not the case, since there are several phenotypes of people.

As not all general conclusions correspond to particular data, it is considered that induction can serve to describe true facts. For example, that group of newborns cry when they are hungry or that those explorers are white.

However, the conclusion will not always be true, as its premises. In any case, it is likely to be true.

You may be interested: Difference between inductive and deductive method.

Steps of the inductive method

The application of the inductive method requires a series of steps that, if applied correctly, will result in a greater probability that the conclusion is correct.

1. Data collection

It is the selection of the series of events to analyze. For instance:

“All the cars that pass through the main avenue at 12 noon will be analyzed.”

2. Observation

It consists of examining each event separately to detect characteristic features. Continuing with the previous example, it would be:

“Cars that pass through the main avenue at 12 noon have wheels, windows, seats and doors.”

3. Pattern identification

It is considered which characteristics are repeated in all the selected events. For instance:

“The observed cars have 4 wheels.”

4. Conclusion

A general conclusion is drawn from the observed patterns. In this case, the conclusion would be:

“All cars have 4 wheels.”

Inductive reasoning characteristics

The method of reasoning based on induction has a series of characteristics, among which the following stand out:

  • They provide knowledge : the conclusions drawn are not contained in the premises, thereby revealing new data. For this reason, it is a method so widely used in empirical sciences, since it is a tool for generating knowledge.
  • The conclusion is a probability : the premises can be true, and yet the conclusion can be false. But if the premises are true, there is a greater probability that the conclusion is.
  • The conclusion is not in the premises , but in the relationships that are established between them.

What is deduction?

The deductive method is another form of logical reasoning used in the scientific world to verify the veracity of certain data.

An example of the deductive method would be:

All the planets in the Milky Way are hemispherical.

The planets of the solar system are hemispherical.

Earth is a planet in the solar system.

This is the reason why it is said that the deduction goes from the general to the particular, since the premises contain generic data from which a conclusion is drawn that applies to a specific event.

Transferred to the field of scientific research or production of knowledge, deduction makes it possible to rely on proven or accepted theories to describe the phenomenon being studied and make inferences about it.

Inference is applied through the deductive method, which in turn has two types:

1. Direct deductive method

The researcher uses a premise from which he draws his conclusion, without contrasting it with others. For instance:

  • Premise A : the planets are not cubic.
  • Conclusion : the Earth is not cubic

2. Indirect deductive method

The researcher requires two or more premises to draw a conclusion. For instance:

  • Premise A : the planets are not cubic.
  • Premise B : Earth is a planet
  • Conclusion : the Earth is not cubic.

In both cases, the objective is the same: to take some general characteristics and adapt them to the particularities of the phenomenon to draw conclusions. These conclusions, in turn, serve to validate the theory or objective knowledge used in the research.

Steps of deductive reasoning

The deduction-based method has 4 stages, which are applied in both the direct and indirect methods:

1. Data collection

It consists of defining what facts or events will be analyzed. For instance:

The shape of the planets in the solar system.

2. Observation

To build the premises, it is necessary to observe the phenomenon. Observation, in turn, has as many stages as there are premises to be created. The second premise, and those that follow it (if any), will always be used to contrast the first and thus confirm its veracity. For instance:

  • Premise A : the planets are not cubic.
  • Premise B : Mercury is a planet.
  • Premise C : Earth is a planet.
  • Conclusion : the Earth is not cubic.

3. Conclusion

With the data extracted from the general premise, and after contrasting them with the rest of the propositions, a particular conclusion is made. In this case:

The Earth is not cubic.

Characteristics of deductive reasoning

The deduction reasoning method has elements that are essential to be considered a way of generating knowledge:

  • The conclusions do not provide new knowledge : the deductive method only describes or confirms already known phenomena.
  • If the premises are true, the conclusion is true , otherwise, it means that some of the premises (or all of them) are false or that the deduction was not made correctly.
  • The premises contain, in themselves, the conclusion : the task of the researcher is to find the hidden data in the propositions to arrive at a logical deduction.

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