One of the variables which governs appropriacy is purpose. We decide what- we want to say on the basis of what purpose we wish to achieve. Do we wish to invite? To agree? To congratulate? All these purposes have been called language functions, since to say ‘Congratulations’ to someone actually performs the function of congratulating as soon as the word is out of your mouth. ‘I promise’ performs the function of promising. With such words the relationship between word and function is easy. It is more complex when a superior says pointedly to someone else in the room ‘It’s very hot in here’ in such a way that he or she is clearly requesting the other person to open the window.