- Imagination - including induced by EMF, drugs etc. It can be quite reasonably argued that our imagination creates many manifestations. However, just because something presents itself from our imagination, that doesn't make it any the less frightening - or dangerous. Remind me to post about Ouija boards!
- Staining. In this case, a place (usually) is stained by strong emotion. It is like the mental state of someone who previously resided there - and who may or may not still be alive - has impregnated the environment. Usually this is a negative thing - a depressive thing. There's nothing to see, and in fact there is no 'spirit' or 'ghost' there - just a stored set of emotions.
- Recording. This is a classic haunting scenario. The ghost walks past, possibly with some appropriate sound and so forth. But there is no ghost. Somehow, in ways we don't understand, the environment has been left with a recording of the past that some are able to pick up. It is like staining but rather than a feeling, a recording involves sensory stimulation.
- Tulpas. Tulpas are also called 'thought-forms'. The result of mental concentrations, these are a type of 'mind' that is created and which often can assume an almost independent existence. In reality it is closer to a computer - i.e. no self-awareness, just programmed. Rare. Very rare.
- Poltergeist. If you've seen the movie then forget it. Poltergeist activity is actually psycho-kinetic energy - i.e. energy that can move objects. Mostly (but not exclusively) it is derived from the subconscious of living human beings - frequently pre-pubescent children. As the child encounters various hormonal changes, these can also trigger sub-conscious psycho-kinetic powers that cause noises, movement of household items and so forth.
- Bound Spirits. Ghosts. The 'souls' or awareness of those who have died. Normally the death process is exactly that - a process. There are many beliefs regarding what happens once the process of death has occurred but in the case of bound spirits, that process is not fully completed for some reason. Unfinished business is the popular explanation though every case differs. Bound Spirits are essentially trapped - usually by their own obsessions, guilt, fears, ignorance etc - and once correctly moved on, cease to present issues.
- Entities - positive, negative, benign. There are more things in Heaven and Earth and there are more 'things' than ghosts. Different religions give them different names - Angels and Demons being just two. They are sentient and they are here for different reasons. Dealing with them - when necessary - requires experience and skill. They are also not very common.
- Time slips - when people from another time cross into this or vica versa. Ever found that a journey you always take one day takes only half the time? There's no explanation for that except to say you read your watch incorrectly. But there are many cases where 'time slips' seem to occur, ranging from lost time to gained time, from seeing a glimpse of the past to witnessing something from the future. In this case we are not talking about the skill of prophesy - we are describing a situation where some freak link between now and a different time has opened up. Fantasy, fiction or fact? Hard to say, harder to prove.
- Dimensional slips - as above but 'beings' from different dimensions. Don't think time, think dimensions. OK, stop thinking them because it will hurt your brain. Creatures that don't exist appearing for short times, parallel universes - it sounds like the thing of science fiction but may not be that impossible. Quantum physics has opened up numerous new concepts including the multi-verse and who is to say that others in other universes are not playing with their own large hadron colliders.....
There are many types of paranormal manifestations that can be encountered. This list is not exhaustive but it does cover the essential varieties. Nor may all actually exist. Come to that, some - although perceived as paranormal - may not in fact be so :