Youcat commented through CCC – Question n. 326.

YOUCAT Question n. 326 - When does an authority act legitimately?

(Youcat answer)  An authority acts legitimately when it works for the sake of the Common Good and applies just methods of attaining the goals thereof.    

A deepening through CCC

(CCC 1903) Authority is exercised legitimately only when it seeks the common good of the group concerned and if it employs morally licit means to attain it. If rulers were to enact unjust laws or take measures contrary to the moral order, such arrangements would not be binding in conscience. In such a case, "authority breaks down completely and results in shameful abuse" (John XXIII PT 51).    

Reflecting and meditating 

(Youcat comment) The people in a State must be able to rely on the fact that they live under a “government of laws”, which has rules that are binding for all. No one is obliged to obey laws that are arbitrary and unjust or that contradict the natural moral order. In that case there is a right, or in some circumstances even the duty, to resist.

(CCC Comment)

(CCC 1921) Authority is exercised legitimately if it is committed to the common good of society. To attain this it must employ morally acceptable means. (CCC 1904) "It is preferable that each power be balanced by other powers and by other spheres of responsibility which keep it within proper bounds. This is the principle of the 'rule of law,' in which the law is sovereign and not the arbitrary will of men" (CA 44).

(The next question is: How can the common good be promoted?)