What are A Priori and A Posteriori?

"A Priori" and "A Posteriori" - two mysterious yet powerful terms that have deep philosophical roots, but are quite often encountered in our everyday speech. Both words come to us from Latin, where a priori means "from the previous," and a posteriori means "from the subsequent." These terms not only enrich our vocabulary but also open doors to complex questions about how we know the world and what knowledge we can consider reliable.

A Priori is knowledge that we obtain independently of any experience. It is what we know before we interact with the world or gather facts. This may seem strange: how can one know something without any experience? But philosophers argue that such knowledge truly exists.

The philosopher Immanuel Kant was one of the most influential thinkers who developed the idea of a priori knowledge. He explained that we have built-in structures for understanding the world, such as mathematical knowledge. After all, none of us discovers that 2+2=4 through experiments. We do not learn this through observation or experience. This knowledge exists within us a priori - prior to any experience, and does not require proof. The same situation applies to logic: the rules of logic are a priori because they underlie our thinking.

Another example is geometry. Euclidean geometry, which is studied in school, is based on axioms that do not require proof. They simply "are." For instance, the fact that a straight line is the shortest distance between two points is perceived as something obvious and self-evident. This knowledge is a priori because we do not have sensory confirmations for it - it arises from the very nature of our thinking.

In contrast to a priori knowledge, a posteriori is knowledge that we acquire through experience, observation, and experiments. This is knowledge that emerges after we have directly encountered reality.

For example, you cannot know that water freezes at 0°C until you see it with your own eyes or receive such knowledge from others. This knowledge is gained through experience, and it is not "built-in" to your mind like mathematical or logical knowledge. This is a typical example of a posteriori knowledge.

Another example: we learn that summer is warmer than winter only through observations and experiences of living through different seasons. Such knowledge is the result of our direct contact with the surrounding world.

Immanuel Kant was one of the first philosophers to thoroughly develop the concept of distinguishing knowledge into a priori and a posteriori. He emphasized that our knowledge is not limited to just one of these types. Both types of knowledge are important, and they complement each other.

Rationalist philosophers, like René Descartes, emphasized the role of a priori knowledge - that which we can know only through reason, independent of sensory experience. For them, reason was the primary source of truth. For example, Descartes believed that the existence of a person could be proven a priori through reason, rather than through experience. His famous phrase "Cogito, ergo sum" ("I think, therefore I am") is one of the examples of knowledge that can be obtained independently of sensory data.

In contrast, empiricists, like John Locke or David Hume, emphasized that our mind is a sort of "blank slate" on which we record knowledge only after we learn about the world through experience. For them, all knowledge is a posteriori, and we cannot know anything without experience.

In modern life, we rarely think about which knowledge we acquire a priori and which is a posteriori. However, these concepts occur more often than it seems.

In everyday conversations, the word "a priori" is often used when we want to emphasize something obvious, something that does not require proof. For example, the phrase: "It is a priori clear that one must study mathematics for success in science" means that this knowledge is perceived as an axiom, as something self-evident.

On the other hand, a posteriori we acquire knowledge through experience. For example, when you say: "Now I a posteriori know that without planning, the trip will be chaotic," it means that your experience has given you this knowledge.