Full Idea
A concept of the understanding, which contains the general rule, must be supplemented by an act of judgement whereby the practitioner distinguishes instances where the rule applies from those where it does not.
Gist of Idea
General rules of action also need a judgement about when to apply them
Source
Immanuel Kant (True in Theory, but not in Practice [1792], Intro)
Book Reference
Kant,Immanuel: 'Political Writings', ed/tr. Reiss,Hans [CUP 1996], p.61
A Reaction
This is Aristotle's phronesis, and Hart's 'rules of recognition' in law courts. So is the link between theory and practice an intellectual one, or a sort of inarticulate intuition? I like 'common sense' for this ability.
Related Idea
Idea 20932 Positive law needs secondary 'rules of recognition' for their correct application [Hart,HLA, by Zimmermann,J]