THE CLOSE examination of the dialogue of a scene from any play will reveal the fact that normally a character is given three or four sentences, depending upon their length, in which to express a single thought or feeling. If, for instance, in a greeting there is some reason why the audience should know the degree of warmth in the greeting it is apt to be expressed in several sentences; as "Hello. How are you? I'm glad to see you again. Where have you been?" If the greeting is expressed in a simple "Hello," then the actor would assume that the author did not think it necessary to define the relationship between the characters.
There is an old rule of playwriting that if you want an audience to know anything you should repeat it three times. There is something about the psychology of an audience which requires that the attention be directed onto a given subject for a certain length of time for a large group of people to be impressed with the subject. If two characters merely greeted each other by saying "Hello" there would not be sufficient time for the greeting to become effective in the consciousness of the audience, but the more extended form of the greeting which includes several more sentences allows the audience time to be aware of the fact that the two characters have seen each other and have experienced a certain degree of pleasure or displeasure in so doing.
A simple exercise will illustrate the problem. Let one character greet another character, saying, "Hello. How are you? I'm glad to see you again. Where have you been?" Invent whatever actions seem appropriate to these lines. Then repeat the exercise using only one word of greeting, "Hello," but assume that the character's thoughts and feelings remain the same -- that he is equally glad to see his friend, that the thought passes through his mind that he hasn't seen his friend for a long time, and that he wonders where the friend has been. The actor will immediately discover that it is impossible to convey these thoughts to the audi