To communicate a threat, one has to communicate the commitment that goes with it, and similarly with a promise; and to communicate a commitment requires more than communication of words. One has to communicate evidence that the commitment exists; this may mean that one can communicate a threat only if he can make the other person see something with his own eyes or if he can find a device to authenticate certain allegations.

DEFINE: Distinguishes communicating a commitment (which needs evidence/authentication) from merely communicating words.

Thomas C. Schelling, The Strategy of Conflict, loc. 342