Validity is the property of what it is valid. This adjective (valid), which comes from Latin valĭdus, alludes to what results consistent, plausible, or admissible.

For example: “An excuse of this type is not valid in a field like this”, “The judge considered that the defense attorney’s request was valid”, “Red containers are not valid in this promotion”.

Validity refers to what is consistent or acceptable.

## Validity in logic

The concept of validity appears in different contexts. In the field of logic, the validity of an argument is the property that is evidenced when the conclusion is implicit in the premises. It is important to note that an argument can be deductively valid, even if its conclusion is not true.

The next argument It has validity from the logical point of view but its conclusion is not necessarily true:

1. If we are not in April, then we are in May.
2. Today we are not in April.
3. So, we are in May.

While the argument is deductively valid, its conclusion may not be true (it is possible that “Let’s not be in April” and that neither “Let’s be in May”).

A deductive reasoning can have validity in terms of logic but offer a conclusion that is not true.

## Disjunctive syllogism

The scheme used to determine if an argument is valid is called disjunctive syllogism, since it presents two options (which we can call p Y what), eliminates one and, therefore, allows us to deduce that we are facing the other. Let’s see an example below, which may be similar to the previous one, although it is not the same:

1. The document is in the right or left drawer.
2. It is not in the drawer on the left.
3. So it is in the drawer on the right.

In a case like this, it is enough to determine the validity of the schema to know if its arguments are also valid, and this is possible by means of the semantics (if it is not possible that the conclusion is false and the premises true) or syntactic (The scheme is valid if there is a deduction of the conclusion starting from the premises and the axioms, using only the allowed rules of inference).

## Validity in inductive reasoning and deductive reasoning

Logic also contemplates the inductive reasoning, which consists of studying the tests that give rise to the estimation of the probability of a series of arguments, in the same way as the rules for the construction of strong inductive arguments.

This differs from deductive reasoning, described in previous paragraphs, in that it is not possible to determine if an argument is valid; For this reason, when we are faced with an induction, we must evaluate its strength, that is, the degree of probability of obtaining a true conclusion if the premises are also true.

## The concept in science and at the legal level

In the field of epistemology, a knowledge is valid when a certain scientific community recognizes it as true and coherent. If a person who defines himself as ufologist maintains that the Earth was created by Martians, it is likely that the scientific community does not consider said “knowledge” as true and, therefore, the statement lacks validity.

Of course, the validity of a theory or an unprecedented statement can not always be evaluated in a short time, but usually a lot of tests and checks are necessary, some of which depend heavily on events that are difficult or impossible to reproduce by force.

History has shown us that science can commit mistakes, since it is not absolute but evolves along with the rest of human knowledge. For this reason, something that today is considered invalid may become an irrefutable truth within a few years, as has happened on many occasions.

Finally, at the legal level, the validity of a rule depends on the satisfaction of material and formal requirements by the same.