Human memory is a strange thing and can play tricks. Sometimes a long-forgotten memory reappears in a dream or hallucination, and you think it's something new to you. For example, you were once told or read about an 'orrible murder' in some haunted house in the past, and forgot all about it. Years later you re-visit the house and experience the long-forgotten memory in an hallucination. Then - you ask one of the locals and he thoughtfully 'refreshes' your memory about the 'orrible murder' - and here we are with a clear case of precognition!
At least, that's one rational way of looking at it.
Ghosts can be of people you have known in the past, who have since died. For instance, my father died in 1971. Sometimes I still have a dream with him in it, doing something anachronistic like browsing the internet or using a mobile phone. That's just a wrong association of memories that often happens in dreams. It doesn't mean my father has appeared in the present day 'as a ghost'...
At least, that's one rational way of looking at it.
Ghosts can be of people you have known in the past, who have since died. For instance, my father died in 1971. Sometimes I still have a dream with him in it, doing something anachronistic like browsing the internet or using a mobile phone. That's just a wrong association of memories that often happens in dreams. It doesn't mean my father has appeared in the present day 'as a ghost'...