Full Idea
Every action which by itself or by its maxim enables the freedom of each individual's will to co-exist with the freedom of everyone else in accordance with a universal law is right.
Gist of Idea
Actions are right if the maxim respects universal mutual freedoms
Source
Immanuel Kant (Metaphysics of Morals I: Doctrine of Right [1797], Intro C)
Book Reference
Kant,Immanuel: 'Political Writings', ed/tr. Reiss,Hans [CUP 1996], p.133
A Reaction
This idea shows the moral basis for Kant's liberalism in politics. If all individuals acted without contact or reference to other individuals (a race of hermits) then that would appear to be optimum moral right, by this standard.