User blog comment:Auslly~Bobbie~Music/Talk Like Crazy!/@comment-6156346-20130509215517

Paradox Suppose a man traveled back in time and killed one of his grandfathers (say his paternal grandfather) before the traveler’s father was conceived. The traveler would then never have existed and hence could not have traveled back in time. In this case, however, his grandfather would not have been killed, and hence the traveler could have been born and traveled back in time.