A Facebook friend just asked me: "Just quickly, what is speech act theory in a nutshell?"
Words do things. To speak is to act. We don't want people to simply listen to us, but to be impacted by what we say and respond in some way. Eg: you asked me a question - you want your words to act upon me in such a way that I respond by providing you with information concerning speech-act theory. Which I have now done. I take it you don't want me to respond to your question by writing a thesis on speech-act theory, rolling it into a scroll, squeezing it into a nutshell, and handing it to you...
The intended impact of a particular unit of discourse depends on its context.
Eg: Fred says to George: "the door is open."
Does Fred mean:
- It's cold - could you shut the door, please;
- Take the opportunity while you have the chance;
- Get out!
- Something else...?
It depends on context - what Fred & George's relationship is like; where they are; what they've been saying to each other... etc. When communicating in person, we discern nuances of meaning from body language. When dealing with a written text, we need to pay attention to genre ("writing style"), literary and historical context, and author's particular writing style... etc.
Eg: your request for info "in a nutshell" depends on a shared assumption between you & I that by "nutshell" you don't literally mean you want information stored inside the empty shell of a nut, but you want a brief answer. This rambling discourse proves my complete inability to answer anything briefly, nutshell notwithstanding.