Acts and scenes
An act is a part of a play and is defined by elements such as rising action, climax and resolution. A scene is a part of an act defined with the changing of characters.
To be more specific, the elements that create the plot of a play or any story, and divide a play into acts include the exposition, which give information, setting up the rest of the story. Another is the inciting incident, which starts all of the action that will follow. Going along with the inciting incident, the major dramatic question is formed; this holds the rest of the play.
The majority of the play is made up of complications. These are the things that change the action. These complications lead up to the crisis, this is the turning point. Most of the time, at this point, the major dramatic question has been answered. Finally, there is the resolution. This is the end of the play where everything comes together and the situation has been resolved. This leaves the audience satisfied with the play as a whole. These more specific elements of plot in a play are the main things used to divide a play up in to acts and sometimes scenes.
The Roman theatre was the first to divide plays into a number of acts separated by intervals. Acts may be further divided into scenes; in classical theater each regrouping between entrances and exits of actors is a scene, while later use describes a change of setting.
Modern plays often have only one level of structure, which can be referred to as either scenes or acts at the whim of the writer; and some writers dispense with firm divisions entirely. Successive scenes are normally separated from each other in either time or place; but the division between acts is more to do with the overall dramatic structure of the piece. The end of an act often coincides with one or more characters making an important decision. A decision which has a profound impact on the story being told.
Many operettas and most musicals are divided into just two acts, so in practice the intermission is seen as dividing them, and the word “act” comes to be used for the two halves of a show whether or not the script divides it into acts.