Skeptics always ask for proof. Being a science person myself, earlier, I did not believe in ghosts as such, but recent personal experiences did bank me into believing towards them. I recall various other people narrating their experiences to me, but I used to disapprove of them until I got proof, which incidentally never happened. But a spate of bad incidents happened to me, for which I could find no answer, made me helpless, and I had to take the help of a shaman. He could easily solve my problems, and it awakened to me that India is really a land of magic, spirits, and shamans. I discussed with him in-depth about the validity of the other unseen world, and came up with facts that I heard the first time.
The spirit and the body together make our identity. When our body dies, the spirit passes on to a next level of consciousness, where the material world is meaningless and impossible to enjoy. But ghosts are merely restless spirits, whose passing onto the next world is prevented for a number of reasons. For instance, the person may have died with a need to pass on an urgent message, or to accomplish some unfinished task. In some other cases, the ghost may be angered over its betrayal and murder in life, and cannot rest until the one who has committed the crime is properly punished. A ghost might also, through its misbehavior in life, find itself bound to an unhappy existence between worlds, until it finds some sort of way to atone for its actions. A relatively weak spirit might remain under the domination of a greater spirit, who might be continuously tormenting him, and would not be able to rest until the greater spirit is destroyed, captured or set free. Finally, a ghost may just not know that it has died.
And he went on, most of the time; ghosts are the transparent image of a person, usually at the time of their death. Since deaths can be violent, they may have broken necks or gaping, fatal wounds. Others who die more peacefully or perhaps as a result of poison, may show no outward sign of trauma. They are usually clothed in the garments they wore at the time of death, or in what they were fond of wearing prior to that.
In most cases, these spirits are confined to a limited area. Ghosts are usually limited to remain near the area of their original demise. They may, however, wander about the vicinity, although their weakness makes it difficult for them to make their presence known. In some rare cases, they have been known to be tied to particular objects or people―usually something it was fond of in life―accompanying the object when it is removed elsewhere.
Ghosts generally leave no trace of themselves on the real world. During their wanderings, they are usually non-material. They have no odor, and, with some exceptions, cannot manipulate physical objects. Even the sight or sound of a ghost is elusive―like a hallucination, they are only seen and heard in a person's mind. Their presence might otherwise be noted through a gentle wafting of air as they pass by, and some individuals seem to be able to sense their presence psychically. At times, a ghost may be seen and heard by some people in a group, and not others. Many ghosts can select who can sense it, and who cannot. They are non-corporeal, and are usually noticed only by others in a similar state.
One clue that ghosts are present is through encountering certain sounds that are obviously out of place to their surroundings. These creatures can project the sounds that were significant to them in life. This can range from children at play to the merriment of balls and dances, or even just footsteps. The sound will usually seem to be coming from behind a door or a wall, and they will cease when someone living enters the area.
Places where ghosts are particularly strong are known to have lot of visions telling the person(s) seeing it about the way in which they were killed or how they died. These extremely rare and terrifying illusions appear to take people encountering them back in time to when the ghost was still alive. They often reveal why the being was turned into a ghost. People in these visions may freely interact with the illusion, but any attempt to significantly alter the outcome can shatter it. The illusion may continue at different times, or may repeat itself endlessly. No one can predict accurately when a place may experience such an effect, as they often occur on the anniversary of the ghost's death, or other meaningful dates.
A ghosts can give the impression that it is teleporting. It decides to not be visible, then moves to a new spot, and materializes there. They can move through most physical objects unimpeded. Magical things can block ghostly travel. Some are able to materialize into a physical shape. They may be fought with certain mantras, herbs, yantras, and symbols. Most of them can be detected and wavered off by shamans, or persons knowledgeable in this field.
As far as attacking humans is concerned, most ghosts have no real means of attack, other than acting in a threatening manner when their area is trespassed upon. They may, however, possess physical objects for some time, causing, for example, the chimes of a clock to ring, or the strings of a musical instrument to be strummed. The supernatural power of these creatures is such, however, that the mere sight of them, or realization of their presence, can be so frightening as to terrify the observer.
Fighting them off is just a control of your willpower and mental practice against such unnatural instances. People have been sharing their residences with ghosts, and both are living peacefully. Spirits cannot be defined as good and bad, but they are just like most of us, whose feelings and emotions need to be heard by others.
Coming back to 'my' experience, I had accidentally picked a small metal ring from a very old temple near my residence. Apparently, the ring belonged to some miser about 300 years back (I got this information from the shaman I visited). This person was so much attached to this ring, that I kept having terrible nightmares for nearly seven continuous days after I picked up the ring. I barely escaped an accident that could have taken my life.
These experiences and discussions had a profound effect on turning me from a non-believer to a believer. Our world apparently has another world superimposed on it, i.e., the non-material world. Scientists are trying day and night to prove scientifically that this world exists. Scientists are constantly agreeing and disagreeing within themselves regarding this topic. And I have just joined this debate, on which side I don't know, but I sure hope to find out in the near future.