Every work of art has some kind of structure. Just as buildings vary enormously in size and shape, plays too vary in their internal laws and framework. In theater, structure usually takes the form of a plot, which is the arrangement of events or the selection and order of scenes in a play. Plot, in turn, is generally based on a story. This story is brought to life through action, which is based on some sort of conflict or tension. Dramatic structure is based on a set of conventions, which include the limitation of space and time, the existence of strongly opposed and equally balanced forces, and incentive or motivation for the characters. The first scene of a drama starts the action and sets the tone and style for everything that follows. Goals are set for the characters, and obstacles and complications serve as impediments to the attainment of those goals. As a result of conflicts, obstacles, and complications in a play, the characters become involved in a series of crises, which lead to the most significant crisis, referred to as the climax. In the final climax, the issues of the play are resolved, happily or sadly according to the dictates of the genre.