Consistent histories and quantum delayed choice

John Wheeler devised a gedanken experiment in which a piece of apparatus can be altered just before the arrival of particle, and this "delayed choice" can, seemingly, alter the quantum state of the particle at a much earlier time, long before the choice is made. A slightly different gedanken experiment, which exhibits the same conceptual difficulty, is analyzed using the techniques of consistent history quantum theory. The idea that the future influences the past disappears when proper account is taken of the diversity of possible quantum descriptions of the world, and their mutual compatibility or incompatibility.