When Tennessee Williams made the decision to take Big Daddy, the pivotal personality of Cat On a Hot Tin Roof, off stage for the entire final act of the play, it was a bold choice. so bold a choice, in fact, that the original Broadway director Elia Kazan forced Williams to rewrite the last act to fix it.
Film is a director's medium – the final control over a movie is entirely in the hands of its director. The stage, however, is the providence of writers. While a powerful director or a weak-willed writer can make the balance swing in the other direction, it is largely acknowledged that a completed play is what it is, and there's only just so much a director can change without the consent of the author.
The Broadway premiere of Cat On a Hot Tin Roof was a special case. A blockbuster writer and a blockbuster director came together to produce their first play since their most significant achievement together, A Streetcar Named Desire. After their long association Williams greatly respected Kazan, and trusted his instincts. Williams writes in the explanatory note of the published edition of the play that a playwright can hand a director an absolute final play without allowing him access to drafts, or he can find a director who will cave to the writer's every request – and neither is desirable. In Kazan, Williams said, he had found a director he could trust to give perceptive and meaningful notes early on in the process.
And Kazan had major reservations about the first completed draft of the play, the one that is still printed in published editions. As summed up by Williams in his explanatory note, these reservations were:
1) Big Daddy was too vivid and important a character to disappear from the play except as an offstage cry after the second act curtain.
2) The character of Brick should undergo some apparent mutation as a result of the virtual vivisection that he undergoes in his interview with his father in Act Two.
3) The character of Margaret should be, if possible, more clearly sympathetic to the audience.
Williams did not agree with these edits – especially the second, bcause he felt that "a conversation, however revelatory, [never] effects so immediate a change in the heart or even conduct of a person in Brick's state of spiritual disrepair." But he wanted Kazan to direct his play, and he wanted it to be a success, and so he re-wrote the third act to address these concerns.
This revised third act covers much of the same material as in the published version, but compresses much of the dialog to make room for Big Daddy, who storms around the stage, makes some coarse jokes, learns of Maggie's feigned pregnancy, and then exits again to survey his kingdom from the roof. The added appearance by Big Daddy adds nothing to the play except for what it explicitly is – a final connection with the character before the last curtain. Yet for that reason alone, for the mere presence of Big Daddy on stage, it is a substantial change to the feelings of the audience regarding his character. No doubt the act can be (and has been) performed effectively either way, but it is easy to see why Kazan was uneasy about letting such a monumental character fade away unseen.
The one other significant change is to the very end. In the published script, we are left entirely uncertain as to whether Brick will concede to sleep once more with Maggie and allow her to bear a child. The text itself leads one to suspect that nothing is going to change, but with enough ambiguity that each production can choose for itself which ending will be implied.
In the playing script, however, Brick ends the act sitting on the bed – and although the dialog is also quite different from the published script, it is this stage direction that significantly weights the dice in favor of Brick having a change of heart. That big bed has been sitting in the middle of the stage all night, the demilitarized zone of their marriage, and by sitting on it at the end Brick finally crosses that line towards Maggie.
The revised third act played in the Broadway premiere and is often published alongside the original third act. Many high profile productions have used the original script, or Williams further revision of the original for the 1974 revival. Today, a director is given the option to essentially play at being Elia Kazan, and decide which third act of Cat on a Hot Tin Roof is preferred. There's no right answer.