Well it is actually both because there ghost that want attention and some that don't want to be seen. that's mainly what I know how to answer this question.
phoenix wrote this! But of my opinion its a easy question
I'd say it can appear as just about anything. Some may appear as human figures that you can see clearly, some may be a human figure yet just all black (I have seen one of these.. but that's another...
It is the nature of ghosts that they do not appear in response to human summoning. Many ghosts do not seem to be aware of the presence of living persons at all.
A ghost might appear because: It died unfairly such as murder and their murder was never caught. It has some unfinished business...love/ it was tried or accused unfairly/family/ it has to send a...
Usually ghosts appear when they have been killed by a certain SOMETHING and have come back to haunt that certain THING. Even though maybe there is a ghost in your house and it is haunting you doesn't...