Principles of Inquiry                        Discussion project: The A Posteriori and the A Priori

 

Here are several propositions.  Try to decide which of them can be known a priori and which depend on evidence (and thus can be known only a posteriori):

 

  1. 2+3=5
  2. If you have two koalas and three kangaroos, you have five animals.
  3. If Perth is west of Adelaide and Adelaide is west of Sydney, then Perth is west of Sydney.
  4. Perth is west of Sydney.
  5. George W. Bush is the President of the United States.
  6. The President of the United States has the power to veto legislation passed by Congress.
  7. No bachelor is married.
  8. No goose is purple.
  9. No goose is a fish.
  10. If you work hard, you will succeed.
  11. If you lose all the hair on your head, you will be bald.
  12. Everything that has a color has a shape.
  13. Everything that has a shape has a size.

 

 

Here are several classical arguments for the existence of God.  Try to decide which of them is a posteriori and which a priori:

 

The Ontological Argument

 

  1. God is, by definition, the most perfect being.
  2. A God that exists is surely more perfect than a merely imaginary or fictional God.
  3. So, God exists.

 

 

The Argument from Design

 

  1. If we examine the natural world we find many intricate and intricately related structures.  (Think, for example, of the human eye and of the way our power of sight enables us to meet our needs.)
  2. Quite generally, when we find intricately structured objects we suppose that intelligent designers created them.  (Think, for example, of finding an object on the beach, examining it, and discovering that it was a working timepiece.  Surely we would assume that it had been made by some intelligent designer, not that it had just grown, like a seashell.)
  3. So, we should also infer that the intricate structures in nature are the product of intelligent design.
  4. So, God exists.

 

 

A Cosmological Argument

 

  1. It is a self-evident truth that every event must have a cause.
  2. But the chain of cause and effect cannot go on forever.
  3. So, there must be a First Cause.
  4. So, God exists.