A posteriori knowledge is

based on experience, on observation of how

things are in the world of changing things. A priori

knowledge is based on reasoning rather than

observation.

Your knowledge that it is raining outside is a

posteriori knowledge. It is based on your experience,

your observation of what is happening out side. One couldn’t figure out whether it was raining

or not by just reasoning about it. Now consider

the following questions: (1) Are there any

married bachelors? (2) What is the sum of 38 and

27? After a bit of thought, you should conclude

that there are no married bachelors, and 38 + 27

= 65. You know these things a priori. You didn’t

need to make any observations about what was

happening. You just needed to reason.

One important question about a priori truths

is whether they are all analytic, or whether there

are some synthetic a priori truths. The philosopher

Kant thought that (1) above was a priori and

analytic, whereas (2) was a priori and synthetic.

See analytic and synthetic for further discussion.

An a priori argument is one that uses no empirical

premises. An a priori concept is one that is innate

or could be acquired just by using one’s

reason.

See also analytic and synthetic; contingent

and necessary; matters of fact and relations of

ideas.

a priori See a posteriori and a priori.

argument from analogy See analogy.