When I wrote a week ago about natural authority, I left out an important aspect of the discussion: power.
Again, I will examine this question from an etymological perspective, and from the perspective of exousia in Rom. 13:1. If you look up exousia in a dictionary, you will find several possible definitions besides "authority," one of which will be “power.” Another way of seeing this is to think of the “authorities” in question as “the powers that be.” The two expressions seem to be functionally equivalent, at least in many circumstances.
If you look up the Neo-Vulgate translation of Rom. 13:1, you find the Latin word potestas, which means “power.” For instance, the power possessed by the tribunes of the people in republican Rome was called potestas tribunicia.
If you look up the German translation of the same passage, you will find St. Paul admonishing the Romans to submit to the state's Gewalt, or “the state’s power.” Gewalt, however, is much more than mere power; it implies violence. For instance, a derivate of this word, vergewaltigen, means “to rape.”
These three possible translations of exousia show that there is considerable overlap between the concepts of authority and power. On the one hand, authority and power are not identical. After all, might does not make right. On the other hand, authority and power cannot be completely separated. Indeed, authority without power is a joke.
Is there any way to understand power and authority? The neatest way of thinking about this is, I believe, as follows. Authority can be defined as the right to use force, and power can be defined as the ability to use force. These two terms, however, are not mutually exclusive; instead, power needs authority, and vice versa. They each complete the other.
My discussion is, of course, completely inadequate for such a complicated topic, so I hope some of you will contribute your insights.