"Radical drama," Graham Murdock notes...
...sets out to present a critical perspective on the present social order.
This means it contemplates and studies socioeconomic groups within society. The idea is that "power and privilege...permeate everyday life." These socioeconomic elements stymie the chance for people to more clearly know themselves, and also inhibit "social change."
...radical drama probes the idealizations and rationalisations that justify the present order.
In this case, things that are seen as natural elements of society are brought into question, as one searches for the reality vs. the ideal in civilization at the time in which the drama takes place.
Radical drama questions the substance of society, concentrating on wealth and power—and realistically assesses how these things hinder development of members and classes of society, which can have an undesirable effect on the rest of society.
This kind of drama was first introduced in the Boston at the turn of the century (in the 1890s).
...radical drama and independent theater [entered American society]...dealing with contemporary social and moral problems...
"Radical drama" today would most likely not be called by that name as the term "radical" has changed since 1890, and again since the 1960s. However, the concept significantly addresses social issues, especially that apply to the rich who control much of what occurs throughout the social realm—especially with those not controlling great wealth. Ironically, the concerns of "radical drama" are very much the same today as when they were first conceptualized.
It would seem that maintaining focus on the plot of the "radical drama" is important to preserving the integrity of the drama's intention.
Henrik Ibsen's Norwegian play, A Doll's House (1879) might well fall into the category of "radical drama," as it took a very close look at the Torvalds (an upper-class family) and drew a stark comparison with the lives of two other main characters, Kristine Linde and Nils Krogstadt—both struggling to survive while those of wealth faced a much easier life. It also examined timely moral issues. The play was very "radical" for its time!
"Post-dramatic theater" is very different. Hans-Thies Lehmann recognized the elements of this dramatic movement with the publication of his book at the end of the 20th Century, identifying...
...tendencies and stylistic traits occurring in avant-garde theatre since the end of the 1960s.
Immediately the difference between the "radical drama" and "post-dramatic theater" is apparent, as this newer concept sacrifices the story's plot to something it perceives to be of greater significance...the audience. It is...
...more striving to produce an effect amongst the spectators than to remain true to the text.
In summary, it would seem that while "radical drama" intended to bring to the attention of the public social concerns, the "post-dramatic theater" was not satisfied with informing the public—but was more intent upon changing the way the audience reacted to the information conveyed.
...postdramatic theatre knows no "plot" at all, but concentrates fully on the interaction between actors and audience.
Throughout the history of drama, the plot has been essential to one's understanding of the play. In "post-dramatic theater," the plot disappears, and the significant activity on stage is an exchange between actors and spectators—that becomes of paramount importance.
Radical drama and postmodern theatre: First, the terms drama and theatre have to be cleared up: Drama is a literary term meaning “imitation of an action by language without narrator (Aristotle). Theatre is imitation of an action by means of action, and is a physical art form that may or may not have a literary component. Post-modernism refers to innovations after the modern era of realistic staging and naturalistic themes—domestic struggles such as those dramatized by Henrik Ibsen (Doll’s House, etc.) and Anton Chekhov (Three Sisters, etc.), the two linchpins of modernism. By the middle of the 20th century, post-modern playwrights like David Mamet and Sam Shepard were departing from modernism into post-modern drama. At about the same time, however, theatre radicals were rethinking every part of the theatrical metalanguage; the Living Theatre (Julian Beck and Judith Malina), the Open Theatre (Joe Chaikin), the Performance Group, and a dozen similar theatre groups throughout the world were rethinking the playwright’s role in the metalanguage, breaking the fourth-wall convention of modern theatre, combining dance with their performances, and confronting the conventions of audience’s expectations. Their “radical” theatrical practice was fueled by the socially radical ideas in society at the same time; thus, “radical” theatre was radical in content as well as in style.