Truth versus Mendacity
A preoccupation with telling the truth, having the strength to accept the truth, and withholding the truth runs through Cat on a Hot Tin Roof. Big Daddy thinks he has just learned the truth when he is told, after extensive medical examinations, that he merely has a spastic colon and not cancer as he had feared. But this is not the truth; his worst fear is realized when Brick, in a moment of anger tells him that he is, in fact, dying. Brick has let out the big secret in response to Big Daddy's unveiling of Brick's secret truth—that Brick drove Skipper to the suicidal use of alcohol and drugs when he hung up on Skipper's attempt to "confess" his homosexual love for Brick. While Brick believed that the confession resulted directly from Maggie's jealous pressure upon Skipper, he also feared that he and Skipper's love would be misunderstood, even though it was the most "true" thing he had ever known.

Rather than face the truth of his role in his friend's death, Brick withdraws from the world, complaining that it is full of lies and liars ("mendacity"). His hatred for mendacity is a trait he shares with his father, Big Daddy, although the two men fail to recognize the extent to which their values correspond. Big Daddy has learned to live and thrive within a world of mendacity. Although he appears crass, he cares about Brick. While Big Daddy has learned to live with lies, his son cannot, turning to liquor to escape not only from liars but also from the horrible truth about Skipper's death. Brick gives no indication of the impact his discussion with Big Daddy has had on him; he remains aloof (and drunk) throughout the rest of the play. It becomes clear that Big Daddy, who lived with mendacity, had a healthier means of keeping himself true than does his son

Homosexuality
When Cat on a Hot Tin Roof was first staged, its main theme was widely thought to be homosexuality. Williams denied this, and the play itself, after entering a more sexually permissive era, demands acknowledgment that homosexuality is not its central concern. Brick's love for Skipper, he insists— and both Maggie and Big Daddy affirm—was a platonic, non-physical love. That the physical aspect of their love is never resolved in the play indicates the discomfort and ambivalence over homosexuality that existed in the 1950s. Was Brick in love with Skipper, or was theirs the simple and profoundly deep love of friendship that Brick proclaims it to be? Brick had had a satisfactory relationship—sexual and otherwise—with Maggie until her jealousy of Skipper prompted her to disrupt the careful balance the three of them had achieved. Can two men who love each other also participate in a physical, sexual relationship without harming their status in society? This question reverberates in the play because the answer as to whether or not Brick and Skipper physically consummated their love is precluded by Skipper's death. Writers often "kill off" a character whose actions or presence contradict or threaten society's most cherished mores, thus raising a question without openly challenging the society with an explicitly stated answer.

Idealism
In this play, idealism opposes life itself, with its messiness and its impure combination of good and bad. When Brick tells Big Daddy that he drinks out of disgust with mendacity, he reveals that he is an idealist. Big Daddy explains to his son that he too feels surrounded by mendacity, it thrives in his family, in the church, in his clubs, even in himself, forcing him to make a pretense of liking it all. But Big Daddy is a realist—he keeps his ideals separate from his life. Big Daddy enjoys living: his idea of celebrating his new lease on life is to find a woman, "smother her with minks and hump her from hell to breakfast."

Brick, on the other hand, eschews sexual passion absolutely, looking up at the cool moon as a model of the ideal detachment he wants in his life and relationships. Brick's form of idealism is an escape from life Maggie refuses to let him escape, however. She accuses him of feeling a passion for Skipper so "damn clean" and incorruptible that it was incompatible with life—"death was the only ice box where you could keep it," she tells him. Maggie defies Brick's sterile idealism, his death-in-life oblivion achieved through alcohol, and she demands that he cure it with life—by fathering a child.