The problem of criterion

Guarding the gates of knowledge is an ancient and terrible creature who poses this riddle to anyone who wishes to pass:

“to know whether things really are as they seem to be, we must have a procedure for distinguishing appearances that are true from appearances that are false.  But to know whether our procedure is a good procedure, we have to know whether it really succeeds in distinguishing appearances that are true from appearances that are false.  And we cannot know whether it does really succeed unless we already know which appearances are true and which ones are false.  And so we are caught in a circle.” How do we escape the circle?

From The Problem of Criterion, by Roderick Chisholm.

By the way, Chisholm is not that terrible creature – he merely tells of that riddle. Here is a picture of Chisholm describing the horrific creature to a mortified student.

Put another way, the quest to understand knowledge goes through 2 questions:

(1) What do we know?

(2) What is the criterion for determining when we know something?

It seems we cannot answer (1) unless we first have the answer to (2). After all, how can you tell if you truly know something without first having the proper criterion to determine that? Yet it seems (2) cannot be answered without (1). How should we know if the criterion is the right one unless we can show that it truly separates what we know and what we don’t? But that requires us to know what we know.

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