Philosophers often contrast personal authority to authority vested in offices. Some such distinction is traditional and sometimes useful. But it does not provide us with an exhaustive classification of the types of authority, for there is a third type of authority that I shall argue is more fundamental than these two. Let us start with the types marked out by the usual distinction.

Consider first the sort of authority illustrated by the following sentences:

1. (1) Smith is an authority on physics.

2. (2) Smith has (some) authority as a physicist.

3. (3) Smith's views (utterances) on physics have (some) authority.

4. (4) O.K., I believe you—after all, you're the authority on physics!

A person is an authority in virtue of possessing extensive knowledge of a field or subject-matter. There seem to be no limits on what the field or subject-matter can be—for instance, one can be an authority on trivia.