Ostensibly "The Lady or the Tiger" is a story about justice, that is, the only kind of justice possible in fiction--poetic justice. The end of the game played by the semibarbaric king has only two alternatives, and they are quite purposely the conventional alternative endings of comedy or tragedy--marriage or death.
The fact that this particular story "ends" before it ends, giving the reader the freedom to choose a conclusion, is a game on Stockton's part to exploit the reader's need to "close" a story, to see true justice enacted. Stockton urges readers to close the story not by choosing what they want to come out of the doors, but rather in the way readers always achieve closure--by looking back at the plot, the tone, and the thematic motifs to determine the story's thematic "end."
Since the story makes quite clear that the semibarbaric nature of the princess consists of her being both lady-like and tigerish, what readers ae really asked to decide is which aspect of the princess dominates at the end--her lady side or her tiger side. Because the presentation of what goes on the princess' mind makes quite clear which side that is, the reader is not so free to choose as it first appears.
An interesting film version of this story in the Short Story Showcase Series distributed by Encyclopaedia Britannica places the story in a modern setting and relies heavily on montage to structure the events The film manages to capture the satiric intent of the story and to suggest the numerous ironies in the story, most of which focus on the concept of pure justice as being that which is uncontaminated by human knowledge or choice.
The story is most interesting, however, for its focus on the reader's need for closure. For even though the story leaves little doubt that the tiger pounces out at the end (for the princess has more tiger in her personality than lady), most readers feel somehow tricked or cheated that the author leaves the final choice ostensibly open.
Tomorrow: Henry James's "The Real Thing"