1. Unity of Action
In other words, no matter how many events you place one after another—no matter how you pile incident upon incident—you will not have a plot unless you so inter-relate them that the removal of anyone event will destroy the whole story. Each event must depend on the one preceding it, and in turn form a basis for the one following, and each must depend upon all the others so vitally that if you take one away the whole collapses. [1]
[1] See Aristotle, Poetics, Chapter VIII, and also Poe's criticism, The American Drama.
(a) Unity of Hero is not Unity of Action. One of the great errors into which the novice is likely to fall, is to believe that because he makes every event which happens happen to the hero, he is observing the rule of unity. Nothing could be farther from the truth—nothing is so detrimental to successful plot construction. [2]
[2] See Freytag's Technique of the Drama, p. 36.
Aristotle tried to correct this evil, which he saw in the plays of the great Athenian poets, by saying: "The action is the first and most important thing, the characters only second;" and, "The action is not given unity by being made to concern only one person."
Remember, unity of action means unity of story.
(b) Double-Action is Dangerous to Unity. If you have a scene in which two minor characters come together for a reason vital to the plot, you must be extremely careful not to tell anything more than the facts that are vital. In long plays the use of what is called "double-action "—that is, giving to characters necessary to the plot an interest and a destiny separate from that of the chief characters—is, of course, recognized and productive of fine results. But, even in the five-act play, the use of double-action is dangerous. For instance: Shakespere developed Falstaff so humorously that today we sometimes carelessly think of "Henry IV" as a delightful comedy, when in reality it was designed as a serious drama—and is most serious, when Falstaff's lines are cut from the reading version to the right proportions for to-day's stage effect. If Shakespere nodded, it is a nod even the legitimate dramatist of today should take to heart, and the playlet writer—peculiarly restricted as to time—must engrave deeply in his memory.
The only way to secure unity of action is to concentrate upon your problem or theme; to realize that you are telling a story; to remember that each character, even your hero, is only a pawn to advance the story; and to cut away rigorously all non-essential events. If you will bear in mind that a playlet is only as good as its plot, that a plot is a story and that you must give to your story, as has been said, "A completeness—a kind of universal dovetailedness, a sort of general oneness," you will have little difficulty in observing the one playlet rule that should never be broken—Unity of action.
2. Unity of Time