A key theme in Cat on a Hot Tin Roof revolves around the fixation on truth, the bravery required to accept it, and the choice to conceal it. Big Daddy believes he has discovered the truth when he is told, after extensive medical evaluations, that he has a spastic colon instead of the cancer he feared. However, this is not the actual truth; his worst fears are confirmed when Brick, in a moment of anger, reveals that Big Daddy is indeed dying. Brick discloses this heartbreaking secret in retaliation for Big Daddy revealing Brick's own hidden truth—that Brick's actions led Skipper to suicide through alcohol and drugs after rejecting Skipper's attempt to "confess" his romantic feelings for him. While Brick blamed Skipper's confession on Maggie's jealousy, he also feared their love would be misconstrued, despite it being the most "authentic" bond he ever felt.

Instead of facing his role in Skipper's death, Brick withdraws from reality, lamenting that the world is filled with lies and deceit ("mendacity"). This disdain for dishonesty is something he shares with his father, Big Daddy, yet neither acknowledges how much they have in common. Big Daddy has learned to prosper in a world laden with deception. Despite his gruff demeanor, he genuinely cares for Brick. While Big Daddy has found a way to live alongside lies, Brick cannot, turning to alcohol to escape both from deceivers and the harsh truth about Skipper's death. Brick remains unaffected by his conversation with Big Daddy; he stays detached (and intoxicated) for the remainder of the play. It becomes clear that Big Daddy, who managed to live with mendacity, had a more effective coping strategy than his son.

When Cat on a Hot Tin Roof premiered, many audiences thought its main theme was homosexuality. However, Williams denied this interpretation. As society grew more open about sexuality, the play itself suggests that homosexuality isn't its central focus. According to both Maggie and Big Daddy, Brick's love for Skipper was platonic and non-physical. The ambiguity around their physical relationship reflects the 1950s' unease and uncertainty about homosexuality. Was Brick in love with Skipper, or was their connection simply a deep friendship, as Brick insists? Brick had a satisfying relationship—both sexually and otherwise—with Maggie until her jealousy of Skipper disrupted their fragile harmony. Can two men love each other physically without harming their social reputation? This question remains unresolved in the play, as Skipper's death leaves the physical nature of their relationship unanswered. Authors often "kill off" characters whose behaviors challenge societal norms, thereby raising questions without offering clear answers.

This play explores the tension between idealism and the inherent chaos of life, with its blend of virtues and flaws. When Brick admits to Big Daddy that his drinking is driven by a disdain for deceit, he exposes his idealistic tendencies. Big Daddy, on the other hand, confesses that he also feels engulfed by dishonesty, whether from his family, his church, his social circles, or even within himself, compelling him to pretend to accept it all. Despite this, Big Daddy is a realist who distinguishes between his ideals and his everyday existence. He cherishes life and expresses his newfound enthusiasm by declaring his desire to find a woman and "smother her with minks and hump her from hell to breakfast."

Conversely, Brick distances himself from sexual passion, idolizing the cool moon as a symbol of the ideal detachment he seeks in his life and relationships. For Brick, idealism is an escape from reality, a route Maggie refuses to let him pursue. She accuses him of nurturing a passion for Skipper that is so "damn clean" and pure that it cannot coexist with life—"death was the only ice box where you could keep it," she asserts. Maggie challenges Brick's barren idealism and his alcohol-fueled escape, urging him to engage with life by becoming a father.