In many ancient cultures, the word "demon" (or more commonly "daemon") didn't necessarily have the evil connotations that it has today. It simply meant that the being was of a spiritual nature rather than a mortal. Most of the ancient gods of myth were considered "daemons" at some point. It wasn't until Catholicism came into power that we get the same interpretation that we have today.
The words "Demon" and "Demonic" in modern terminology have a direct connotation with evil. The Devil himself is considered to be a demon - a spirit who in modern mythology seeks to consume or command the souls of mortals.
But the term "demon" is often generalized as meaning "evil spirits", becoming less and less specific the more they become generically "evil". I wouldn't consider every ill-intentioned spirit to be a demon. An angry spirit who has yet to move on, for example, isn't necessarily a demon, even if they cause trouble or are, in fact, evil. Demons are of a higher-ranking nature. They have the power to cross over and affect our plane of existence, if only for a little while at a time. They are very, very powerful and potentially dangerous beings.
The most common purpose of a demon is thought to be demonic possession - the overtaking of a human's body in order to claim its soul. At least, this is the most popular interpretation of their intentions. People who are victims of demonic possession become controlled to various extents by these evil spirits. The demon may try to physically harm the person or their family, but usually they seek to scare them. Why? Because excessive fear makes a person weak.
As a demon weakens its victim it gains more and more control over him or her. As it gains more control it gets closer and closer to its ultimate goal - to own the soul of the victim. Why they seek mortal souls most certainly has to do with gaining power and growing stronger. In the world of the human, power is seductive. In the world of the demon, power is everything.
The List of Demon Names
Below are the names of the 72 demons listed in the Ars Goetia - a subsection from the Lesser Key of Solomon.
The first thing to understand about demons and other spirits is that they don't truly exist in our plane of existence. That is, they do not have a corporeal, earthly form. We, on the other hand, do. This is a key advantage for humans.
As you may have noticed from demonic stories, demons don't get to wander free at full force in our world. If they did they would have destroyed and corrupted everything by now. Instead, they only have temporary power that can be used here - unless they find a way to gather more.
Think of it like swimming. We can dive down into the water and hold our breath for some time. While we're there we can make a mess of things, or simply see what's going on. After a short while, though, we run out of oxygen and need to come back to "our world" on the surface. This appears to be the same with demons. They can "hold their breath" and come into our world for a time, but they can't stay for too long.
The exception comes in a similar way as swimming. Just as a diver can go for longer dives with a breathing apparatus, so can a demon take longer stays on our plane of existence if they have a way of doing so.
So what is the "oxygen" that demons need to stay longer? The answer is energy. Spiritual energy is by far the strongest, though spirits have been known to drain batteries, heat, and light among other sources. Energy is energy in a sense, but comparing spiritual energy to electricity is like comparing a nuclear reactor to a car battery. Both can power a light bulb with ease, but they're still not in the same ballpark in terms of strength and range.
To put it simply, demons feed off of energy. Now, just as electricity is polarized (positive or negative), so is all energy. This is exactly what people are referring to when they talk about positive and negative attitudes. We largely ignore these types of personal or spiritual energies because they can't be measured very well on a scientific scale. All that means is that we don't have the technology or understanding needed to measure them, not that they don't exist. If you don't believe me, try getting a dog to listen to you. Smart dog owners know that you don't have to say a word, you just have to change your energy and your dog will pick up on it much better than if you are yelling commands.
The key to keeping demons from affecting you is to learn how to control your energy. Evil spirits need negative energy while positive spirits need positive energy. It's just like a battery - it doesn't work backwards. By starving a demon of negative energy you are effectively suffocating it from this world, just like a diver with no oxygen. No matter what techniques you use to do this, the key is to remember that removing negative energy is the engine that makes it work.
Controlling your personal (spiritual) energy is actually pretty simple. As yogis and zen masters can tell you, it takes a lot of practice to get really good at it, but what doesn't? No matter how good or bad you are at controlling your energy, you can always get better, so there is absolutely no reason not to start practicing this today (especially if you are concerned about evil presences around you.)
Some emotions come from subconscious responses to stimuli, but most of our emotions can be controlled with our thoughts. In fact, even the subconscious responses can be trained over time using this same technique. Just as a karate master knows how to block a punch before he has time to think about it, your subconscious can be trained to automatically respond in a certain way. That comes later, of course, but it isn't really any different from what we're talking about here - controlling your thoughts is the key to controlling your energy.
Being aware of these irrational thoughts and fears is the first and most crucial step to getting rid of them. They can be replaced with positive thoughts and responses just by "rewiring" your logic and connecting the stimulating events with either positive or neutral responses. It's surprisingly simple, yet far too often ignored.
So back to the demons... Demons feed off of negative energy, so if you get rid of the negative energy the demon has less power, less time in our plane, and thus less effect on people and things that exist in our plane. Understanding this is VITAL to keeping evil away. Energy attracts like energy, so if you are putting out positive vibrations, you will not only be attracting positive vibrations, but you'll also be repelling negative ones!
Fear is the #1 source of negative energy. In fact, if you trace most other negative emotions back they turn out to be a sub-form of fear. Think about how you react when you are in a scary situation. Psychologists call it a "fight or flight" response. When faced with danger or fear you get an adrenaline rush that helps you do one of two things - either stand and fight or run away. Both are survival instincts, and neither is inherently good or bad. The problem though is that the emotions that come with fighting tend to be anger and fear, and those that come with running are mostly fear. All negative feelings.
This is how demons get their power. As I mentioned, they start of fairly weak in our plane of existence. Just tourists on a bus passing through. They can watch what's going on, but they don't have much effect over anything. Give them a day pass, though, and they'll mix in like they belong.
If you let demons scare you, anger you, or consume your thoughts you are effectively giving them the exact energy they need to get stronger. This is foolish! Luckily energy is not permanent though, and it takes a lot of energy for a demon or other evil entity to exist in our world. Even if you've fed the beast for years with your fear, anger, anxiety, and sorrow... stop. Resolve to rid yourself of the negative energy, no matter how long it takes or how hard it seems. At the very least get to the point where your reactions to scary events and feelings are neutral. Clear your mind and tell yourself that everything is just fine. If you know how to meditate, this is the perfect time to use it. If you don't know how to meditate, learn.
Over time you can actually make yourself unafraid, and with more time you can view spirits with a detached curiosity rather than a terrified reaction. As you learn to accept your own fear of the unknown, you will actually become stronger and will automatically begin to detach from the fear itself.
Some people use rituals to cleanse people, places, or things that are believed to be cursed. What's important to remember is that it's not actually important what item or ritual is used, but that you believe that it works. Like I said before, it doesn't really matter what method you choose to get rid of a demon because it's all coming from the same basic premise - getting rid of negative energy and replacing it with positive (or at least neutral) energy.
The reason many Catholics choose exorcism rituals is simply because that's what they believe works. Other religions use other techniques because they believe that those techniques work for them. The key is knowing that positive energy is ALWAYS more powerful than negative energy. If you believe that all things are connected in the universe through our energy, as I do, then it becomes pretty easy to realize that you have an incredible amount of energy at your disposal. The energy that created all things is still in all things (even scientifically speaking everything and everyone in our universe is, at our cores, just collections of energy).
This source energy is called different things by different people - God, Source, Flow, Tao, etc. It's not really important to define it, only to believe that it exists. If there are rituals that make you feel powerful in a positive way, include those while you transform your energy and the energy surrounding you in a positive way. It's the belief that you are stronger than the demon (which is true) that gives you true power.
Part of ridding your life of demons is learning to face your own "demons". That is, identifying and confronting the things in your life that are negatively out of balance. It starts with something as simple as cleaning your house - it is well known that messy or dirty surroundings attract negativity and by extension evil. If you are lazy, exercise. If you are overweight, go on a diet. If your boyfriend abuses you, leave him. I know this doesn't sound like great demon-fighting advice, but it is, in fact, the best advice you're likely to get. It's much harder to clean up your mind when your surroundings are a mess. As you go through and sort out your thoughts, go through and sort out the rest of your life as well. It doesn't have to be overwhelming - that's another thought that can simply be challenged and changed.
As physics will tell you, momentum is a great way to sustain the direction of energy, so start making positive changes RIGHT NOW and build on them - a little every day. Ignore the negative things in your life and they will go away. Choose positivity in everything you do and soon you will be nothing but positive energy.
The best way to start is by literally cleaning up your surroundings. If you are disorganized, start finding places for things to be, if you need to vacuum the floors, do it now. A messy life is a huge cause of stress, which is negative energy, which invites in more negative energy, which is like leaving food out for any malevolent spirits around.
If you feel overwhelmed, just pick one thing to clean up a day, one habit to start working on. Every little bit will make you stronger and the culmination of your efforts will show you how powerful you really are. You may not need an exorcist after all. You may be able to create enough positive change that the demons will starve and like any beast, will soon go find somewhere else to feed.
With enough practice demons will have no interest in you anymore.