We must conclude, from the above discussion, that Putnam has not satisfactorily explained how a person can go back in time and thus has not offered any compelling reason why we should accept his description of Oscar rather than his objector's description. However, earlier in our discussion, a possible way to show that Oscar did go back in time came to light: namely, if it could be shown that Oscar2 was at B at t 1 because Oscar1 entered the time (...) machine at t 2. Thus, if backward causation were possible, such backward causes could be used to send a person back in time. But whether backward causation is a conceptual possibility or not is the topic for another paper. (shrink)