A Posteriori vs. A Priori

Attribute	A Posteriori	A Priori
Knowledge source	Based on experience or empirical evidence	Independent of experience or empirical evidence
Justification	Justified by observation or experience	Justified by reason or logic
Examples	Snow is white (based on seeing snow)	All bachelors are unmarried (based on the definition of bachelor)
Contingency	Contingent on empirical facts	Necessary and universal

Definition

A posteriori and a priori are two terms used in philosophy to distinguish between types of knowledge or justification. A posteriori knowledge is knowledge that is dependent on experience or empirical evidence. This means that a posteriori knowledge is derived from observation or sensory experience. On the other hand, a priori knowledge is knowledge that is independent of experience. It is based on reason, logic, or intuition rather than observation.

Origin

The terms a posteriori and a priori have their roots in Latin. A posteriori means "from the latter" or "after the fact," while a priori means "from the former" or "before the fact." These terms were popularized by the philosopher Immanuel Kant in his Critique of Pure Reason, where he used them to categorize different types of knowledge.

Examples

Examples of a posteriori knowledge include knowledge gained through sensory experience, such as the knowledge that the sky is blue or that water boils at 100 degrees Celsius. These are facts that we can only know through observation. On the other hand, examples of a priori knowledge include mathematical truths, such as 2+2=4, or logical truths, such as "all bachelors are unmarried." These are truths that we can know without having to observe the world.

Justification

One of the key differences between a posteriori and a priori knowledge is the way in which they are justified. A posteriori knowledge is justified by empirical evidence. For example, if we want to know whether it is raining outside, we can look out the window and see for ourselves. A priori knowledge, on the other hand, is justified by reason or logic. We can know that all triangles have three sides without having to measure every triangle in existence.

Necessity and Contingency

Another important distinction between a posteriori and a priori knowledge is the distinction between necessity and contingency. A priori knowledge is often considered necessary, meaning that it could not be false. For example, the statement "all bachelors are unmarried" is necessarily true because it is part of the definition of a bachelor. A posteriori knowledge, on the other hand, is often considered contingent, meaning that it could be false. For example, the statement "it is raining outside" is contingent because it depends on the current weather conditions.

Scope

A posteriori knowledge is often seen as having a wider scope than a priori knowledge. This is because a posteriori knowledge is based on empirical evidence, which allows us to learn about the world around us. A priori knowledge, on the other hand, is limited to truths that can be known through reason or logic. While a priori knowledge is more certain, a posteriori knowledge allows us to discover new facts about the world.

Criticism

Both a posteriori and a priori knowledge have been subject to criticism in the field of philosophy. Critics of a posteriori knowledge argue that it is limited by our sensory experiences and can be influenced by biases or errors. Critics of a priori knowledge argue that it is too abstract and disconnected from reality. Despite these criticisms, both types of knowledge continue to play important roles in philosophy and epistemology.