Propositional logic is a system made up, in the first instance, by propositions. Likewise, it contains connective elements that allow working with such propositions in order to generate increasingly complex sentences . Within the world of propositional logic, methods are proposed that allow explaining different common phenomena. One of the best known and used by everyone is the tautology .


What is tautology?

A tautology is nothing more than a formula that is true from every possible perspective. Thus, any proposition of a tautology will always be valid , although to corroborate this fact it is required to use an instrument known as the truth table or truth value table , which allows identifying the propositions involved in a statement and calculating the combinatorial of them . The word tautology comes from the Greek tauto-, which means “the same” and -logy, which implies action. Thus, etymologically, it means “action of the same . 

  • Meaning of tautology
  • Antonym
  • Characteristics of a tautology
  • Function
  • How is it different from contradiction and contingency?
  • Importance
  • Examples of tautology

Meaning of tautology

It includes the formulation of prepositions in such a way that a valid truth can be constructed in any context, and for this the truth table is used, an instrument devised by an American scientist in 1880 . From this point of view, the value in the table should always be V, which does not depend on the truth or falsity of the propositions but on the way in which they are related to each other from the syntactic point of view.



The antonym of tautology is the contradiction, since the first indicates a proposition that is true in all senses, and the second implies falsehood from any point of view, even if the propositions that constitute it are true.

Characteristics of a tautology

To be considered a tautology, a formula must contain the following characteristics

  • It must constitute a specific proposition
  • It must have truth value from any perspective , and therefore be considered a model of truth
  • It must mean a model of truth, but it does not represent a principle of reality


The repetition implied in tautology, although it can come to be seen as something vacuous, allows to create a model of the truth whose content is protected from misinterpretation , helping those who receive the information to understand it more clearly.

How is it different from contradiction and contingency?

The main difference between tautology, contradiction and contingency , is that the first of them implies that the statement is always true , whether its propositions are true or false, while the second will always be false , regardless of the veracity of its propositions, and the third it includes both falsehood and truthfulness .


Tautologies are important in that they allow an idea to be emphasized. Its repetitive nature can be seen, at times, as something superficial ; however, they are useful not only to enhance content but also to somehow protect it from the misinterpretation that naturally occurs in human communications.

Examples of tautology

There are numerous examples of tautological propositions, due both to the lack of knowledge in the use of the language, from the rhetorical point of view, and to the interest in making the matter being discussed in the conversation sufficiently clear. Some of them are the following:

  • “I’m going down the stairs”
  • “I’m going to project a plan for the future”
  • “I am seeing the situation with my own eyes”
  • “The dawn came earlier than the morning”
  • “Our store will be closed until we open”
  • “Kiss me with your beautiful crimson lips”
  • “As a judge I have executed just justice”
  • “I laughed with a loud laugh”
  • “I’m going to go outside to buy some groceries”
  • “I will go up to the attic to better observe what happens”
  • “I will go into your room to clean the furniture”
  • “I require the antecedents prior to your breakup”
  • “I have many future projects”
  • “The triangle is a figure made up of three sides”
  • “We are going to completely fill the stadium”
  • “I really did not expect this surprise from you”
  • “I am a woman or I am not a woman”
  • “The car is red or it is not red”
  • “What I told you during that conversation means what it means”
  • “What color was Simón Bolívar’s blue horse ?”
  • “My white cat meows”
  • “My smart phone is smart”
  • “I told you I won’t, and no way will I”

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