I'm never very certain, my grandfather is a spiritualist who believes that he can perceive and talk to the dead, I've always perceived this as far fetched and yet he has taught me various things, some of which others would refer to as magic and others idiocy such as perceiving auras..
That in itself is simple and scientifically founded given that all people generate a kinetic energy field about them individual to a person as such if this is possible ghosts as they are may be as well..
As to encounters with them I have read a lot about them but never seen one...Personnally I find the history and study of angels far moire interesting....