Authoritative speech
There are various more or less familiar acts by which to communicate something with the reasonable expectation of being believed. We can do so by stating, reporting, contending, or claiming that such-and-such is the case; by telling others things, informing an audience of this-or-that, or vouching for something; by affirming or attesting to something’s being the case, or avowing that this-or-that is true.
What do these acts have in common? Each is an instance of the kind of speech act known as an assertion.