Definition of A Posteriori and A Priori

These two Latin expressions have a leading role singular in the world of philosophy, but they are also used in everyday language. A posteriori literally means "after" and a priori means "before" or "before".

Two ways of knowing

Philosophers like Aristotle and later medieval scholastics differentiated two sources of knowledge: reason and reason. experience. From reason we can reach conclusions without the need for any observation empirical and, therefore, it is a priori knowledge. From the experience of what we observe we make affirmations, which are a posteriori.

In Kant's theory of knowledge

This philosopher established new criteria to define scientific knowledge. For this he proposed a distinction between the different types of trials. In a priori judgments, no information based on experience is provided (for example, the line is the shortest distance between two points) and in a posteriori judgments the truth or falsity of the same must be based on experience (for example, some birds are yellow).

Traditionally, it was understood that analytical judgments (those in which the predicate of a sentence is already contained in the notion of subject) were a priori, while synthetic judgments (those in which the predicate of the sentence is not included in the idea of ​​subject) were a posteriori. However, for Kant this interpretation it is not valid for establishing scientific judgments and for this reason he argued that scientific claims must be synthetic a priori judgments.

In other words, a statement or judgment will have scientific validity if it increases knowledge and, at the same time, if it has universal value.

With this analysis Kant achieved a double objective. On the one hand, it revealed a valid criterion for handling a scientific language in a rigorous (judgments that are not synthetic a priori will not be acceptable from a scientific). On the other hand, he proposed a solution to integrate two traditionally irreconcilable currents: empiricism and rationalism.

In common parlance

The expression a priori is equivalent to others, such as beforehand, beforehand or in advance. In turn, the expression a posteriori means the same as after or posteriorly.

In the language of everyday life, both are used in a different sense than tradition philosophical.

Fotolia photos: Natalia9 / Stocken