The class of speech acts that are called 'performatives' have the property that they are false unless uttered and become true by virtue of being uttered. Notice how such utterances can't be falsified or confirmed:
(11) A: I second that motion.
B: ??That's false
B': ??No, you don't.
(12) A: I dub thee Sir Walter.
B: ??Too true
B': ??I doubt it.
Performatives also have the property that they typically occur in the first person. This can be seen in the oddness of "hereby" with the 3rd person "She" in (13), the fact that the description of what the 3rd person "He" does in (14) does not have the force of creating the bet the way the 1st person variant would, and the lack of apologetic force with the 3rd person "They" in (15):
(13) She (hereby? / thereby?) declares them man and wife.
(14) He bets her ten bucks the Cubs will win.
(15) They apologise.
The examples in (13-15) are not ill-formed. The point is that they are just plain assertions. Likewise, the examples in (16-19) are not ill-formed but in order to work as performatives, they would need to be in the present tense:
(16) I declared them man and wife.
(17) I could bet you ten bucks the Cubs will win.
(18) I have sentenced you to five years in jail.
(19) I am apologising.
What performatives bring to light is the importance of distinguishing truth from felicity. This is a theme that runs through much of Pragmatics. Most of the sentences that we are dealing with in Pragmatics are licensed by the grammar, but they are only appropriate in certain contexts. The grammar can be said to overgenerate and we must identify the pragmatic constraints that are at play which rein in the multitude of ways of saying something and help pinpoint what is most appropriate in a given context.
Performative sentences carry felicity conditions. They are as follows:
First, There must be a conventional procedure having a conventional outcome. The circumstances and persons must be appropriate, as specified in the procedure. For example, not everyone can effect change in the world by uttering (20). It matters who says it, who the listener is, and what the marital circumstances of that speaker-hearer pair currently are. You can't divorce someone who you never married. You can't divorce someone who you already divorced. You can only utter (20) (and have it take its consequence) to a current spouse.
(20) I hereby divorce you.
Second, the procedure must be executed correctly and completely. Examples (21) and (22) highlight the importance of correct execution.
(21) ??I hereby arrest you.
(22) Marriage vows: Do you...
a. ??Yes.
b. ??I am.
Third, there are requisite thoughts, feelings, and intentions, as specified by the procedure that must be in place. If consequent conduct is specified, the relevant parties must follow through. This can be seen in the requisite feelings (or lack of feelings) on the part of the people involved in a wedding annulment (that they never loved each other) or the expected payment for a bet (that the money must in fact be paid).
What are the consequences of violating the conditions listed above? Well, most of the conditions are easily detected and such detections are labeled misfires (e.g., your instructor Hannah says "I hereby place you under arrest"). What is harder to detect are abuses which arise when the requisite thoughts/feelings/intentions are violated.
To go on to section 6.3 on "Speech acts and felicity conditions", click here.