Improvisatory

Edward Albee in The Paris Review:
I find that when my plays are going well, they seem to resemble pieces
of music.
After a certain point, I make experiments to see how well I know the characters. I’ll improvise and try them out in a situation that I’m fairly sure won’t be in the play. And if they behave quite naturally, in this
improvisatory situation, and create their own dialogue, and behave according to what I consider to be their own natures, then I suppose I have the play far enough along to sit down and write it.