competence

The general sense, and the one the word's doublet shares: competence and competency both go back to Late Latin competentia, the first borrowed through Middle French compétence. Used this way it is a mass noun with no plural. It readily takes qualifiers that name a whole field of ability. Intercultural communicative competence, for one, is something language teachers are now required to teach.

Here the noun becomes countable, and that changes how it behaves: a person can have several competences, each one a defined skill such as public speaking. Where the general sense describes overall capability, this one itemizes it. That is why it suits training programs that list the core competences a role requires, one by one.

Lawyers and political scientists use it for who may decide, not who is able to. A court acts within or outside its competence, and a parliament may lack legislative competence on a matter. In the plural it names powers divided between governments, such as the division of competences in a federal constitution. Despite the shared word, it is unrelated to skill at a task and says nothing about how well anyone performs.

A linguist's term that only makes sense as half of a pair: competence is what a speaker knows, and performance is what a speaker actually does with it. The distinction lets the slips, pauses and false starts of real speech be set aside from the knowledge underneath. Its fuller name is linguistic competence. Unlike ordinary capability, it is not a measure of how well someone does anything.

Structural geology borrows the word for how stiffly a rock layer holds its shape under stress. A bed of high competence tends to fracture rather than bend, while weaker layers around it fold or flow. Differences in competence between neighboring layers therefore help explain fold patterns. Geologists use the matching adjectives as well, describing beds as competent or incompetent.