The Grandfather Paradox is a proposed paradox of time travel which results in an inconsistency through changing the past. The paradox describes a time traveler going back in time to kill his grandfather before his grandfather meets his grandmother. As a result, the time traveller is never born. But, if he was never born, then he is unable to travel through time and kill his grandfather, which means the traveller would then be born after all, and so on.
- Reference: The Grandfather Paradox