The Portrait of a Lady explores the conflict between the individual and society by examining the life of Isabel Archer, a young American woman who must choose between her independent spirit and the demands of social convention. After professing and longing to be an independent woman, autonomous and answerable only to herself, Isabel falls in love with and marries the sinister Gilbert Osmond, who wants her only for her money and who treats her as an object, almost as part of his art collection. Isabel must then decide whether to honor her marriage vows and preserve social propriety or to leave her miserable marriage and escape to a happier, more independent life, possibly with her American suitor Caspar Goodwood. In the end, after the death of her cousin Ralph, the staunchest advocate of her independence, Isabel chooses to return to Osmond and maintain her marriage. She is motivated partly by a sense of social duty, partly by a sense of pride, and partly by the love of her stepdaughter, Pansy, the daughter of Osmond and his manipulative lover Madame Merle.
As the title of the novel indicates, Isabel is the principal character of the book, and the main focus of the novel is on presenting, explaining, and developing her character. James is one of America's great psychological realists, and he uses all his creative powers to ensure that Isabel's conflict is the natural product of a believable mind, and not merely an abstract philosophical consideration. In brief, Isabel's independence of spirit is largely a result of her childhood, when she was generally neglected by her father and allowed to read any book in her grandmother's library; in this way, she supervised her own haphazard education and allowed her mind to develop without discipline or order. Her natural intelligence has always ensured that she is at least as quick as anyone around her, and in Albany, New York, she has the reputation of being a formidable intellect.
After she travels to England with her aunt, Mrs. Touchett, however, it becomes clear that Isabel has a woefully unstructured imagination, as well as a romantic streak that suits her position as an optimistic, innocent American. (For James, throughout Portrait of a Lady, America is a place of individualism and naïveté, while Europe is a place of sophistication, convention, and decadence.) Isabel often considers her life as though it were a novel. She also has a tendency to think about herself obsessively and has a vast faith in her own moral strength—in fact, recognizing that she has never faced hardship, Isabel actually wishes that she might be made to suffer, so that she could prove her ability to overcome suffering without betraying her principles.
When Isabel moves to England, her cousin Ralph is so taken with her spirit of independence that he convinces his dying father to leave half his fortune to Isabel. This is intended to prevent her from ever having to marry for money, but ironically it attracts the treachery of the novel's villains, Madame Merle and Gilbert Osmond. They conspire to convince Isabel to marry Osmond in order to gain access to her wealth. Her marriage to Osmond effectively stifles Isabel's independent spirit, as her husband treats her as an object and tries to force her to share his opinions and abandon her own.
This is the thematic background of Portrait of a Lady, and James skillfully intertwines the novel's psychological and thematic elements. Isabel's downfall with Osmond, for instance, enables the book's most trenchant exploration of the conflict between her desire to conform to social convention and her fiercely independent mind. It is also perfectly explained by the elements of Isabel's character: her haphazard upbringing has led her to long for stability and safety, even if they mean a loss of independence, and her active imagination enables her to create an illusory picture of Osmond, which she believes in more than the real thing, at least until she is married to him. Once she marries Osmond, Isabel's pride in her moral strength makes it impossible for her to consider leaving him: she once longed for hardship, and now that she has found it, it would be hypocritical for her to surrender to it by violating social custom and abandoning her husband.
In the same way that James unites his psychological and thematic subjects, he also intertwines the novel's settings with its themes. Set almost entirely among a group of American expatriates living in Europe in the 1860s and 70s, the book relies on a kind of moral geography, in which America represents innocence, individualism, and capability; Europe represents decadence, sophistication, and social convention; and England represents the best mix of the two. Isabel moves from America to England to continental Europe, and at each stage she comes to mirror her surroundings, gradually losing a bit of independence with each move. Eventually she lives in Rome, the historic heart of continental Europe, and it is here that she endures her greatest hardship with Gilbert Osmond.