"I promise to pay you back." is an example of a:

1. Austin called such utterances performatives. 2. The action the sentence describes is performed by uttering it. 3. Nominating, sentencing and promising are typical instances. 4. So the promise is a performative utterance. **Why not the others:** A referential statement describes facts, a metalingual remark talks about language, and a phatic greeting only keeps contact. _Source: Wikipedia, "Speech act", section "Performative speech acts" (revision 1377995517)_