# Definition:A Priori (Logic)

## Definition

A priori knowledge is the sort of knowledge which comes from reason alone.

That is, it does not require the exercise of experience to know it.

Thus the truth value of a statement can be decided by a logical argument whose premises are definitions.

## Examples

### Probability

The following is an example of a priori reasoning:

The probability of rolling a $6$ on a fair die is $\dfrac 1 6$.

The truth of the above statement is dependent upon:

the definition of the term probability
the definition of a fair die.

### A Legal Statement

The following is an example of a priori reasoning:

If Fred Bloggs has committed a crime, then he is guilty.

The truth of the above statement is dependent upon the definition of the term guilty, which, in natural language simply means having committed a crime.

Contrast this with:

Fred Bloggs has committed the crime of usury

the truth value of which is dependent upon knowing whether or not he actually did it.

## Linguistic Note

The phrase a priori derives from the Latin for from what comes before.