Contraposition is achieved through the contrast of two opposite things.
The Latin word contrapositio came into Spanish as a contraposition . The term refers to the act and result of contrast : confronting or contrasting one thing with another opposite or different thing.
Contrary rulings
It can be said that a sentence A is contrasted with a sentence B when it is desired to mark the difference between the two, in such a way that the expression highlights the existing opposition. A and B , in this framework, express the opposite.
We must clarify that the sentence can be understood as a way of expressing a proposition , that is, an entity that has a truth value (it is true or false). To do this, it is necessary that it does not have free variables , since these would violate the fixed nature of said value. To judge validity or falsity, logic uses reasoning . This, in turn, is made up of the premises and the conclusions .
Premise is understood, in this framework, as an idea that is constructed as a sentence of an affirmative or negative nature that provides us with data or information regarding the central theme of the sentence. It is also possible to affirm that this part is the background of the reasoning. Finally comes the conclusion, which follows logically from the premise and serves to close the reasoning. This is also known as consequent .
Some examples
Let's look at the term in context using the following example sentences: “The government is analyzing the possibility of exempting some companies from taxes as opposed to preventing tariff increases,” “As opposed to religion, which is based on faith.” , science is supported by empirical demonstrations” , “The price of wheat and corn has accumulated two weeks of decline, in contrast to soybeans, which maintain constant growth” .
Suppose an economist lists the economic achievements of Brazil , Chile , and Uruguay . Then he refers to the problems that Argentina 's economy is experiencing. The analyst, in this way, postulates the Argentine case ( negative ) in contrast to the experience of Brazil , Chile and Uruguay ( positive ).
logical contrast
Logical contrast postulates the existence of a logical equivalence between a conditional sentence and its corresponding contrast. To put the statement of this law into practice, we must invert and deny the antecedent and the consequent, as we can see in the following example: “All soccer players are athletes” is equivalent to “If you are not an athlete, then you cannot be a soccer player.” .
The Greek philosopher and scientist Aristotle , considered the most important figure in Western philosophy, gave shape to this concept through the theory of syllogisms , reasoning that is made up of two premises and a conclusion, and pointed out that by denying a Consequently, we must also deny its antecedent.
There are several conditional forms of an affirmation: implication, contraposition, inversion, conversion and negation. The first corresponds to the original sentence; the second would give us "If he is an athlete, then he is a footballer" ; the denial, "There is a footballer who is not an athlete." However, we are interested in inversion, which should not be confused with contrast, despite their similarity; would be the following: "If he is not a footballer, then he is not an athlete."
To achieve the logical contrast we must invert and deny the antecedent and the consequent.
Proof by contrast
Demonstration by contrast , on the other hand, also appears in the field of logic and takes advantage of the concepts just exposed. A conditional statement can be contradicted when its terms are denied and the direction of the inference is reversed.
A statement and its opposition are logically equivalent. For this reason, this resource is usually used to prove the implication between the antecedent and the consequent, since it is easier to understand than the analysis of the original sentence.