In the philosophy of language and speech acts theory, __performative utterances__ are Sentence (linguistics)s which not only describe a given reality, but also change the social reality they are describing- wikipedia 
In a 1955 lecture series, later published as How to Do Things with Words, J. L. Austin argued against a positivist philosophical claim that the utterances always "describe" or "constate" something and are thus always true or false.
After mentioning several examples of sentences which are not so used, and not truth-evaluable (among them nonsensical sentences, interrogatives, speech acts and "ethical" propositions), he introduces "performative" sentences or illocutionary act as another instance.
- How to Do Things with Words - pdf
# See also - Performative - Performative Science