Philosophers classify statements into a priori and a posteriori.

For the A-Level exam, you must be able to distinguish between them.

Here, we examine the characteristics of each.

a priori

An a priori statement does not require any experience to know whether it is true or false.

Examples include:

• All triangles are three-sided shapes.

• No cat is both black and white all over.

• All Mondays are not Fridays.

The truth or falsity of these statements can be known just by thinking about them.

There is no possible experience that would change their truth or falsity, so it is not necessary to examine any evidence.

a posteriori

An a posteriori statement is true or false depending on what the world is like.

Examples include:

• That shape is a triangle.

  • Not true if, on inspection, the shape turns out to have four sides.

• That is a white cat.

  • Not true if the cat rolls over and shows a black spot on its tummy.

• Today is Monday.

  • Not true (and rather good news) if today is actually Friday.

These statements are true or false depending on what the world is like.

Knowing whether they are true or false requires that you examine the evidence.

Arguments

Arguments can also be classified as a priori or a posteriori.

An a priori argument has only a priori premises.

An example is Anselm’s ‘Ontological Argument’.

The truth or falsity of these arguments cannot be determined by experience. To evaluate them, you must simply think about whether the premises are correct.

An a posteriori argument has at least one a posteriori premise.

Examples include William Paley’s ‘Design Argument’ and Thomas Aquinas’s ‘Cosmological Argument’.

These arguments can only be true if experience verifies their premises.

To evaluate them, you must actually examine the world.