I suggest a new role for authority and interest in the theory of right: Rights can be explicated as sets of prohibitions, permissions and commands, and they must be justified by interests. I argue as follows: (1) The two dominant theories of right—“Will Theory” and “Interest Theory”—have certain standard problems. (2) These problems are systematic: Will Theory’s criterion of the ability to enforce a duty is either false or empty outside of its original legal context, whereas Interest Theory includes in the definition of a right what actually belongs to the justification of the practice within which that right is assigned. (3) I recast the connection between authority, interests and rights in a way that avoids each theory’s standard problem. (4) The resulting theory also has three further advantages: It analyzes rights in terms of very basic and familiar concepts; it mirrors the understanding of rights in actual public discourse, and it is compatible with a wide selection of moral theories. Since its core is about a specific use of modal auxiliary verbs, I call this new theory the “Modal Theory of Right.”