I am not going to attempt to convince you that ghosts are real. Let's face it, regardless of what I (or other people say), most people will remain skeptical until they personally experience something of a paranormal (meaning outside of the normal experience) or unexplained nature.
Skepticism is a good thing. To blindly accept without thinking or questioning can lead someone into the nether regions of reason. Yet when someone goes to the point of refusing to accept that there are still unexplained "things" in this Universe, then they limit themselves for human-kind definitely does not have all the answers to everything at this point in time.
I have a very logical mind and when I run into something that seems "out of the ordinary," the first thing I do is attempt to find a very normal and rational explanation for it. All logical possibilities must be carefully examined. When all reasonable thinking fails, then and only then can the experience be placed under the heading of the unexplained or paranormal.
Some common characteristics of "ghostly activity":
Electromagnetic field changes drastically
Physical objects moving or operating by themselves.
Call them ghosts, call them energy anomalies or simply call them unexplained phenomena... the name or label doesn't really matter. The fact is that strange things happen!
Banshees & Other Damned
If you spend a lot of time wandering alone in Irish bogs you may find yourself listening to the kind of sound that sends proverbial chills down your spine. Its half anguish and half anger, but universally bad news for you. It’s probably the howl of a Banshee, a ghost of a particularly evil person who’s now cursed to wander the earth. It’s crying because it is phenomenally unhappy. We aren’t really sure why as it has seemingly avoided a far nastier fate in Hell, then again, maybe only pathetic whiners become Banshees. Some will tell you that to hear the cry of the Banshee is to die on the spot. Since our friend Bob (who’s got his drinking problem under control) assures us that he has heard one and is not yet dead, we tend to think the immediate death theory is crap. A more reasonable version of the story is that a Banshee only howls to evil people that are soon to die. The fear may serve to convert this into a self-fulfilling prophecy, or there may be some element of genuine foresight here. Banshees are actually one of a larger class of ghosts that we refer to as the Damned. These are spirits that have been cursed (By whom? God?) to wander the earth as punishment for their sins in life. Their only joy in life (death?) seems to be torturing the living. Some like to prey on other evil individuals while others have different targets. These creatures tend to hang out in places where they can easily lead people to their deaths (bogs, cliffs, etc.), particularly at night. Our advice? Avoid dangerous places at night. That will do a decent job of protecting you from creatures that might have attacked you at random; however, you are still in trouble if a Damned soul is after you in particular. This might come about simply because the celestial powers that be decided to send one of their goons to get you, or because you’ve hastened a nasty soul onto its end and now it is back for you. Either way, this can be trouble. Luckily, there is some hope. Of course, you could just turn over a new leaf and become a decent person. Nah. This might be an option if a haunt comes to get you because otherwise you are pretty much toast. However, for the Damned there are other avenues to be explored first. These things are usually anchored to the material world by some item (Jack’s pumpkin lantern) or place (a will-o-wisp’s swamp). If you can find and destroy that you’re in business. Don’t waste any time thinking the thing is all in your mind. Music, particularly from bells and drums, has been reported to at least temporarily drive these creatures away. Oh, you can also try the exorcism option but what kind of holy man is going to help out your sorry soul?
Haunts (Wraiths, Revenants, etc.)
While the Damned retain some level of self-awareness this is usually blinded by their overwhelming misery and hatred of the living. This is not necessary the case for Haunts. Many have basically lost their minds, but others are very much aware of themselves and their surroundings. Some may even still believe themselves to be alive. Usually the ability of the Haunt to manipulate its surroundings and self are based on its will. These things are created when a strong willed human (sometimes even an animal) dies and refuses to pass into the next life. (Okay, we realize this sounds like absolute crap. It probably is. We have a hard time believing that there is a vitalistic force that animates people and that reclaims their spirits when they die. However, it sounds better than anything else we could come up with.) This refusal may be the result of an horrific death, an untimely one, an overwhelming love of some corporeal person or place, or any of a host of other reasons. As each Haunt is a reflection of its human counterpart, each is unique. The haunt of a serial killer may be a violent and terrifying entity, while the haunt of a child who died with her family may be a sullen and tragic figure. There are a few elements that unify this group. First, all our bound to something in this world. To many it is a place, usually where they died or are buried. For others it is an object that they treasured or despised, and for others is an individual that they wish to protect or destroy. Second, all have power (although they might not be consciously aware of it) over their forms and environment. They can alter the temperature of a room, appear ghostly or solid, induce powerful emotions, etc. Finally, all are incredibly dangerous. This is obvious for the spirit of a serial killer, but don’t be fooled by the haunt of the innocent girl. These beings are no longer human and have become profoundly selfish in their narrow existence. Knowingly or not that child may well cause additional car accidents on the bend where she died. So how do you deal with them? These creatures are, almost without exception, victims of a serious obsessive compulsive disorder. They literally can not leave an unfinished crossword puzzle or go past a Magic Eye image without finding the boat. Leaving this kind of stuff in between you and the Haunt is a good delaying tactic. Unfortunately their isn’t a whole lot more you can do. Again, exorcism is an option and many a holy man will help you out even if you are scum, since they see creatures like this as a threat to decent folk. The real problem arises when you create a ghost from that poor soul that you tortured to death in your lab. Unfortunately, a haunt determined to take revenge is probably going to get it. Start praying. Sorry.
Poltergeists (Angry Spirits, Restless Dead, etc.)
Poltergeists are usually considered the least self-aware of any of the ghost classes. They can be created when a large number of individuals are killed (think human experimentation or mass execution) or when a large number of corpses are troubled. (How you trouble a corpse we don’t know, but several famous cases of poltergeists being generated following whole cemetery exhumations indicates that it is possible.) In general they do not present with a visible physical manifestation. At some point in the haunting they may appear as a collection of ghostly figures or as a mass of glowing globes, however they are usually invisible. They are by no means harmless. Their most frequent manifestation is to levitate and hurl many objects around a room. They also can also effect temperature, emotions, visual perceptions. The odd possession of an inanimate object and even direct physical assault are not unheard of. All of these activities are the result of a mass of weak spirits irrationally trying to manipulate a world that they no longer understand. Exorcisms are unlikely to remove them all as only a small fraction of the spirits tied to the given haunting are active at any given time. They are usually more of an annoyance than anything else, but can become more disruptive as time goes on. If they were caused by lifetime suffering there isn’t a lot that can be done (planting daisies is not going to make a mass grave anything else), moving is probably the only option. If they were formed as the result of messing with bodies then returning the corpses to their proper resting places is a good idea although not guaranteed to work. Once you wake a spirit it may not want to go back to sleep. For these, as well as other spirits, standard protective methods (pentagrams, holy wafers, etc.) are unlikely to be effective.