The phenomenon of thought forms is a very simple one, which can become rather complex. They can also be classified into various headings that define their purpose for existence. Basically a thought form is an energetic being that has existence only through the continued Intent of the person creating it. Once the person stops thinking about it, there is no more intent for existence and so the energy that was feeding it dissipates and so does the thought form.
You will find that all things that are done via magic and spell work, are done with energy. Energy is the main foundation to all things. What we experience as the real world we live in is actually just energy that we have created a consensual reality upon in order to experience it as solid and material. When a thought form is created, it may not be seen as material or manifest, but it still exists as a body of energy.
The most common example of a thought form is that which a mob will generate. The mob mind will start with a couple people who are unhappy about something. They will cause other people to feel the same and their energy is then connected to the mob mind, which starts to escalate. After time the energy that is generated by the mob will start to take on a life of its own, it will connect the people and cause their minds and intentions to be focused on that one purpose. As more people join and more energy is fed to the thought form or Group Mind, it will grow and the emotions of the people are affected which leads to the mob moving as one body, as opposed to moving as individual people all trying to express the same thing. All members of the mob will think as one, and this is the thought form that is being fed, which feeds the members of the mob, creating one Group Mind. As soon as the mob has been separated and the people start to think as individuals again, they will often wonder how they got so caught up in the actions.
This classic example is what we would refer to, in many cases, as the Egregore. The Egregore is a thought form that acts to hold a group of people together. As thoughts are added to the Egregore, it grows, but it also allows those connected to the Current of the Egregore to access the knowledge of that group. It is the Group Mind, many individual minds all connected to a common mind. Jung referred to the Collective Consciousness, which we could suggest is an Egregore that encompasses all things, all thoughts, all ideas. This we could then conclude would be what many people consider to be God. That which is all things. However, this may suggest that it is the people on this planet that create God, and in a way they do, but God also creates the people, in a symbiotic relationship. As the Egregore is fed, so too do the people connected to it get fed.
And as the Great Egregore that is THE ALL exists and will continue to exist, so too do smaller Egregores. Each religion will have an Egregore, each school, each business, each society, etc., etc. As long as the group stay together and keep feeding the Egregore, it will remain and will grow. In the magical sense the Egregore will exist with each Order, coven, study group, hof, etc. The members of the magickal group will be able to access the knowledge of the group through the Egregore. It is the god of the group and many Orders have named the Egregore, and they continue to worship it and feed it energy.Another thought form is the Servitor. The definition of a servitor is a person who is at the beck and call of the master. When a magician creates a Servitor through a magical act, the Servitor is given a task to accomplish. Once that task has been completed or the Servitors life span has expired (in most cases the Servitor is given the task and a certain period of time to accomplish it in), then the Servitor is absorbed back into the magician.
The creation of Servitors is always very specific, whereas the Egregore develops over time and remains in existence until the Intent stops feeding it.
In the same lines as the Servitor we also have the Artificial Elemental. The differences are quite apparent. The Servitor is created from the personal power of the Magician, whereas the Artificial Elemental is created through the Elements themselves, those being Fire, Air, Water and Earth. In the metaphysical world we find beings called Elementals. These are the Salamanders, Sylphs, Mermaids, Nymphs, Gnomes, etc. Each one of them is constructed from a specific element. As humans we are made from all four elements, including Spirit, and so we can exist in this constructed world of ours which is also created from all the elements combined to form Earth. As an Elemental, and because of their very specific make up, to exist in this world is very difficult as the elements which oppose them are found to contradict their existence. Therefore, they exist in a parallel reality which can be crossed from this world and vice versa.
The reason I use the term Artificial Elemental in the case of a thought form is because the Elementals do not exist because humans think about them. The Artificial Elemental is an energetic being that is constructed by the Magician from one or more of the Elements. The purpose of the Artificial Elemental will determine which Elements are used.
There are many warnings about working with Thought Forms, more specifically Servitors, and for good reason. I made the following comment in the first paragraph: "Once the person stops thinking about it, there is no more intent for existence and so the energy that was feeding it dissipates and so does the thought form." However, this is not always true. In most cases, it is, but in some the Servitor will actually latch on to another source of energy to feed from. What this means is that once the time span has expired, or the Magician forgets, the Servitor continues to exist because the food source is coming from somewhere else besides the Magician. Never forget that once something exists, it has a level of consciousness. Maybe not quite like ours, but it can function as a thinking entity.
The other thing to remember is the way in which you treat these entities. Because you are the Master of the Servitor, many people think they can boss them around, punish them, treat them like dirt and generally show no regard for them what so ever, just because they are a body of energy that is there to do the Magician's bidding. A Servitor demands the same respect as any person you will meet on the street. You are the Master, but the Servitor is also your "child" as you birthed it, you created it and allowed it to grow. Treat it with respect and love it, but make sure it stays in line. If you kick it around and it does manage to find an independent food source, then it may just come back and show you what it thought of your treatment.
If you are a Clive Barker fan you may have read Ararat, and there is a very good example of a pissed off Servitor in there.
So, do what thou wilt, but play nicely.