Despite challenges from movies, radio, and television, theater has continued to thrive in the twentieth century. Perhaps this is so because of the "live" nature of theater, for theater is an event in which the performers are in the presence of the audience. This creates a circular flow of energy, as performer affects audience and audience affects performer.
This effect is magnified by the fact that theater is a communal event. The group experience is indispensable to theater, as the group reinforces the emotions experienced by the individual and creates a "collective mind." When a collection of individuals respond more or less in unison to what is occurring onstage, their relationship to one another is reaffirmed and strengthened.
In addition, the makeup of the audience can have an effect on the quality of the actor-audience relationship and alter the theatrical event. A homogeneous group of people will affect the performance in one way, a heterogeneous group another.
A degree of aesthetic distance is necessary for theater to be effective. It is essential that the roles of the performer and the observer remain distinct. It is this distinction that separates observed theater from participatory theater. In observed theater, the audience uses its imagination to participate in the play vicariously while separated from the action. In participatory theater, those who take part in the play are not performers in the usual sense, and there is no attempt to follow a written script. The emphasis is on education, personal development, or therapy.
Nowhere is the exchange between actors and audience more evident than in the creation of illusion in theater. While illusion may be initiated by the creators of theater, it is completed by the audience through the use of the dramatic imagination. Two powerful tools of the imagination, which are an important part not only of theater but of real life, are symbol and metaphor.
Theater can mirror life in many ways, presenting aspects of either observable reality or the reality that lies beneath the surface or within the imagination. An audience in a theater is asked to accept many kinds of imaginary worlds. One way to differentiate these imaginary realms is to divide them into what is called realistic and nonrealistic theater. Realism, which became the dominant form of European drama in the late nineteenth century, attempts to recreate life so closely that the audience assumes it must be life. Nonrealism, on the other hand, attempts to transcend observed reality and present the part of life that exists in the mind. However, it is a mistake to assume that these two approaches are mutually exclusive. Most theater performances contain a mixture of realistic and nonrealistic elements.