The deductive reasoning is a type of argument in which the conclusion can be inferred from the premises . It is considered as a method of reasoning that goes from the most general to the particular. A type of deductive reasoning is known as a syllogism which has a fixed structure made up of two different propositions that act as premises and a third proposition that acts as the conclusion of the reasoning.

What is the syllogism?

The syllogism is a type of deductive reasoning that is part of logic and that consists of two different propositions that will turn out to be the premises and a third that will be the conclusion which is necessarily deductive from the other two.

  • Definition
  • Characteristics of the syllogism
  • What is it for
  • Types of syllogism
  • Elements
  • Rules
  • Legal syllogism
  • Importance
  • Examples


The syllogism is a form of reasoning of such deductive having two assumptions older and premise lower and from them will manage to reach a certain conclusion . It is a type of deductive reasoning because from two different judgments it can be inferred into a new one . In this case, the major premise will be the one that works as a starting point and is general, while the minor premise will play an intermediary role and will be less general in order to later deduce theconclusion of reasoning.

Characteristics of the syllogism

Among the main characteristics of the syllogism we find the following:

  • It must contain a total of three propositions .
  • From the two negative premises no conclusion can be reached .
  • From the two positive premises it is not possible to obtain a conclusion that is negative .
  • When a premise is negative then the conclusion will also be negative and vice versa.
  • When there are two premises that are particular , no conclusion can be reached.
  • In the syllogism, the middle term cannot be part of the conclusion.
  • It results from the disposition that it has in the premises depending on its quality which can be affirmative or negative and depending on its quantity that can become general or particular.
  • In the legal field , the word syllogism is used as a support tool for the interpretation of the norm .

What is it for

The syllogism is a method that serves to achieve logical reasoning and is widely used in the fields of propositional logic , in studies related to mathematics and computer science and even in the field of philosophy .

Types of syllogism

The main types of syllogism that exist are mentioned below:

  • Hypothetical syllogism : it is also known by the name of conditional syllogism and it is in which the major premise has an alternative while the minor premise is responsible for affirming or denying one of the alternatives.
  • Categorical syllogism : it is the type of syllogism in which the major premise has the function of affirming or denying. In other words we can say that A is part of C and that B is part of C.
  • Disjunctive syllogism : in this case, the syllogism is characterized because it does not affirm at any time that any of the premises are true, only one of them, but it does not do so simultaneously.
  • Compound syllogism : in this type of syllogism, the major premise turns out to be a compound proposition and the minor premise is then a categorical proposition. In this case, the minor premise will be the one in charge of affirming or denying any of the parties that are making up the major premise.


Regarding the structure of the syllogism, it should be mentioned that it is characterized by being fixed without taking into account the matter that is being dealt with or the natures that the premises have. It is made up of the following elements :

  • major premise : which is equivalent to a predicate of the conclusion.
  • A minor premise: which turns out to be equivalent to a subject of the conclusion.
  • A middle ground : with which the predicate and the subject can be compared.
  • A consequent : also known as a conclusion which is the point that is reached by affirming or denying the relationship that exists between the predicate and the subject.

It is also important to mention that the elements can be related to each other through judgments which tend to have a certain nature always depending on the type of affirmation or denial that has been made. These judgments can be the following:

  • Universal : in this case, the lawsuits are responsible for maintaining that a property is related to all of its elements.
  • Individuals : individual lawsuits are responsible for extending a property over some of the elements that are part of a larger total.
  • Affirmative : affirmative judgments are also known as union judgments and are responsible for proposing an equivalent relationship between the terms of subject and predicate.
  • Negative : negative judgments also called separation judgments are responsible for proposing the opposite of affirmative judgments.


In order to establish a syllogism, a series of rules must be taken into account that turn out to be unbreakable , in other words, they cannot be omitted at any time. The Rules for creating a syllogism are as follows:

  • No type of syllogism can have more than three terms .
  • The conclusion of the syllogism can never be of greater length than the premises .
  • The middle term that is part of the syllogism cannot be placed in the conclusion .
  • The major premise must always be of a universal character since a conclusion that is true cannot be found from particular premises.
  • The conclusion that the syllogism has can never have a universal character than the premises.
  • The premises must be composed with terms that are
  • The conclusion cannot be verified on matters that are not contained within the premises.

Legal syllogism

The legal syllogism is a type of reasoning that can be applied to the precepts of law . In this type of syllogism, the major premise will be constituted by the generic norm , the minor premise will correspond to the specific case and will be constituted by the means of the judgment that the alleged major premise has been made. The conclusion will finally be the sentence by which it will be possible to impute the individuals who are involved in the case.

The legal syllogism within the legal precept then establishes a type of normative hypothesis for an assumption of action that will later determine the consequences and that can be applied within the technical and logistical. The sentence, including all its factual and legal foundations, then adopts the general structure of the syllogism that includes the major premise , the minor premise, and the conclusion .

It can also be defined as an operation of the logical time that can be performed by the applicator to determine whether a specific event in particular manages to match the specific fact legal and should also match the legal consequence that has been established by the standard.


The syllogism has a special importance mainly in the field of logic because this science manages, through the syllogism, to become a science of the first order . It is important because it serves to express the daily deductions of the human being in which one of the two premises is usually given in an implied way. In addition, it is important because it helps to rigorously substantiate the theses that turn out to be controversial since it mainly resorts to the reason for what is said.


Here are some examples of syllogisms:

Example 1

  • All human beings are free
  • Luis is a human being
  • Luis is free

Example 2

  • Some birds can fly
  • Maria likes animals that fly
  • Maria likes birds

Example 3

  • All the planets that exist have a round shape
  • Mars is a planet
  • Mars is round in shape

Example 4

  • No fish can be mammal
  • Whales are mammals
  • Whales can’t be fish

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