Inductive and deductive method

The difference between the inductive and deductive method lies in the direction of the reasoning for reaching conclusions.

Both the inductive and deductive methods are logical reasoning strategies, with the inductive one using particular premises to reach a general conclusion, and the deductive one using general principles to reach a specific conclusion..

Both methods are important in the production of knowledge. During a scientific investigation it is possible that one or the other is used, or a combination of both, depending on the field of study in which it is carried out..

At present, the method used in experimental sciences is the so-called hypothetico-deductive method..

Inductive method

The inductive method is used starting from particular cases to arrive at a general proposition.

The use of inductive reasoning was and is of great importance in scientific work in general, since it consists of the collection of data on specific cases and their analysis to create theories or hypotheses..

Inductive method characteristics

• Follow the direction from the bottom up, from the particular to the general.
• Start from empirical observations and then build theories about what is observed.
• It is still used in science, but within the hypothetico-deductive method.
• It is limited to the observation of phenomena.
• Your conclusions are likely and may turn out to be false.

Observation in the inductive method

Observation is one of the key aspects in the inductive method. The experience of phenomena is important in scientific areas where data from observed facts and phenomena are collected, to arrive at a hypothesis or general theory..

For scientific knowledge to have weight, it is important that numerous observations are made about a fact so that, if similar conditions are met, a generalization can be made.

In addition to observation, the inductive method uses experimentation to obtain the necessary data that lead to a general conclusion.

Steps of the inductive method

• Facts and phenomena are observed and recorded.
• The data collected from various observations and their possible relationships are compared and analyzed.
• Generalizations (or laws) are established.
• These generalizations are used to predict future phenomena.

Examples of the inductive method

A simple example is to find out the result of the sum of the interior angles of a triangle.

First, the internal angles of a triangle are added and it is noted that these give 180º as a result. Then, the same activity is carried out with another triangle, and the result is the same, 180º. This action is repeated (observation and comparison of each sum) several times.

The result remains the same. When all the information is gathered, the general conclusion is reached that the interior angles of a triangle add up to 180º. In other words, from this series of observations and their comparison, it is concluded that this will continue to occur.

Another example occurs when it is observed that all objects that go up tend to fall. If you pick up a series of objects and then drop them, you see that each of them falls to the ground. In this way, the conclusion is reached that there must be some property or force that makes the objects attract each other (in this case the mass of each object).

It was thus that, through this type of observations, the law of gravity, formulated by the English naturalist physicist Isaac Newton (1643-1727). This law basically proposes that all bodies that have mass attract each other. This is how Newton proved it through various observations. It can be said, then, that "every body that goes up has to come down".

Limitations of the inductive method

Science is constantly developing. Even with general laws that predict events or phenomena, science practitioners know that there may be cases in which conclusions do not apply.

This is why the inductive method as such may be insufficient when it comes to building knowledge and broadening the understanding of reality, if its conclusions are not constantly tested..

According to the Scottish philosopher David Hume (1711-1776), there is no absolute certainty that what we observe a certain amount of times will be repeated in the same way in the future.

For the Austrian philosopher of science Karl Popper (1902-1994), the induction problem It is based on the fact that it is not always possible to establish a universal truth, starting from particular observations. For Popper, the important thing is to find facts that can fake (to refute) conclusions in science.

A famous example is that of the statement "All swans are white". At some point in Europe this was believed to be the case. It was observed that the swans were characterized by being all white, this statement being generalized as a fact.

This is because there was no experience to the contrary (black swans had never been seen). However, later on, specimens of black swans were brought from Australia to Europe, and this simple fact refuted the idea that all swans were white..

Deductive method

The deductive method is a type of reasoning used to apply laws or theories to singular cases.

It is the method used in the formal sciences, such as logic and mathematics. In addition, deductive reasoning is key in the application of laws to particular phenomena that are studied in science..

It is a hierarchical form of reasoning, since it starts from generalizations, which little by little are applied to particular cases. This makes the deductive method very useful for producing knowledge of prior knowledge. It is also practical when it is impossible or very difficult to observe the causes of a phenomenon, but the consequences it produces..

Characteristics of the deductive method

• Follow the direction from top to bottom, from general to particular.
• It is the method used in formal sciences.
• It is based on theory to predict observable phenomena through hypotheses.
• The conclusion is contained in the premises.
• If the premises are valid and true, the conclusion is also true.
• Your conclusions must lead to logical and rigorous consequences.
• By itself it does not produce new knowledge.

Examples of the deductive method

A classic example of this method is the following:

• Premise 1: All men are mortal.
• Premise 2: Socrates is a man.
• Conclution: Therefore Socrates is mortal.

It is possible to observe that the conclusion is already implicit in the premises.

Another example occurs when you think about living things and their genetics. All living things are known to possess DNA (deoxyribonucleic acid). Therefore, if at any time a living organism is going to be analyzed, it follows in advance that this organism will have DNA.

Validity and veracity in the deductive method

In the deductive method, erroneous conclusions can be incurred if the premises are not true. For example, considering the following premises:

• Premise 1: All men are bad.
• Premise 2: Your grandfather is a man.
• Conclution: So your grandfather is bad.

This argument it is valid, However, not true. Its validity lies in the fact that the conclusion is implicit in the premises. But the statement contained in premise 1 ("all men are bad") is not a true statement, since its veracity does not follow from the premises, so it is still necessary to verify it..

In this sense, the conclusions of the deductive method are valid and correct when the premises are also correct. In the same way, if the premises are true, the conclusion will also be true..

Hypothetical-deductive method

The method currently used in scientific research is the so-called hypothetico-deductive method. This method basically synthesizes the main aspects of the inductive and deductive method..

Steps of the hypothetico-deductive method

1. The observation and analysis of a series of phenomena.
2. A hypothesis according to the results of what was observed in order to explain these phenomena. For the hypothesis to be valid, it must be possible to test it.
3. When a hypothesis postulates something, it is deduce that if the same conditions that caused a phenomenon are present, the consequences that the hypothesis predicts should be given.
4. I know check the hypothesis from experiments.
5. If the hypothesis is verified, then it is accepted. If your assumptions are not verified, is rejected.

You may be interested in reading:

• Induction and deduction
• Types of research