"A principle does not determine its own application."

A principle requires interpretation before it can be applied.

Example:

Principle:

Freedom of speech should be protected.

Most people agree with the principle.

But they disagree about its application.

Does it protect:

political criticism?

hate speech?

defamation?

threats?

The principle alone does not answer all those questions.

Interpretation is needed.

however, that once a court or legislature adopts a particular interpretation, that interpretation strongly influences how the principle is applied in practice.