Art
The life-affirming significance of art is one the central themes in "The Last Leaf." Art as a subject arises early in the story when the narrator discusses how Greenwich Village is a mecca for artists seeking cheap apartments with good light and architectural character, and O. Henry expands on the theme with a cast of characters who all wish to become artists of renown. Johnsy and Sue have come to New York to pursue careers in art and illustration, and old Behrman—considered by most to be an alcoholic failure—has endeavored his entire life to paint a masterpiece, but he has never found the courage to start it. After Sue tells the doctor of Johnsy's desire to paint the Bay of Naples one day, the doctor dismisses the possibility of art to sustain Johnsy's will to live. However, Behrman's artistic intervention is precisely what extends Johnsy's life: in choosing to paint a leaf so realistic that Johnsy is fooled, Behrman makes good on his promise to paint a masterpiece. In this way, art not only encourages Johnsy to continue to live, it confirms Behrman's status as a great artist, as he dies having proven his inherent talent and value.
Superstition
Early in the story, Sue becomes aware of Johnsy's "fancy": she believes that her fate is somehow tied to the fate of the ivy leaves, and she is certain that her death will result as a consequence of the last leaf falling. In this way, Johnsy's superstition becomes another central theme. Sue and Behrman dismiss Johnsy's illogical and romantic attachment to the dying ivy vine as the fancy of someone whose mind has become weakened by illness. However, Johnsy's ominous feelings toward the ivy vine turn out to be justified when, at the end of the story, Sue and Johnsy learn that Behrman died after contracting pneumonia while painting the last leaf. Therefore, the last leaf falling did precipitate a death.
Willpower
Willpower emerges as another major theme of "The Last Leaf" when the doctor delivers his grim prognosis: he believes Johnsy's chances of survival are slim because she has lost the will to live. He goes on to remark how medical intervention is only effective when a patient uses the medicine in combination with the will to recover. Though she wishes to die, Johnsy's willpower is nonetheless strong: she sets her will toward the goal of dying when the last leaf falls. Through painting the fake leaf, Behrman is able to exploit Johnsy's will and use it against her, for as long as she believes there is one leaf left, she will continue to live, while her body simultaneously fights the infection.
Fate
Fate—the unfolding of events beyond a person's control—is another of the story's major themes. Because of her pessimism and superstition, Johnsy believes her fate is tied to the ivy leaves, which implies that supernatural forces beyond her control have determined her imminent death. The doctor pushes back against this notion, believing that a patient's fate is determined not by forces beyond their control but by their individual will to recover. Fate arises in relation to Behrman as well, as he speaks often about how he is fated to paint a great masterpiece, which he spends his life avoiding. Ultimately, fate reveals itself as significant when Johnsy learns that Behrman met his fate by painting the last leaf, and that her fate and his were intimately entwined.
