The Automatism Theory
Some people believe that you are actually moving it and answering your questions all by your self with out you knowing it. When you have two or more people, you are all thinking together. The Ouija board use to be used as a mind reader, that was the purpose of the board, and that’s how the medium could read your mind. By asking a simple question, you repeat it in your head and then you answer it. But you don’t know your answering it. With the Ouija board you can find things out that you knew, but you didn’t know you knew. It is kind of like automatic writing or the old Planchette. When there is more than one mind answering the questions, it's like all of your thoughts together and you all just think the same thing and spell it without you knowing.
The Spiritualists Theory
Spirits and demons are controlling the board. They can hear you and if you are using something that is a “door way” to the other side, then they will be able to respond. They were people once so they know how to read, write, talk and spell. When you ask a question, the spirit moves the Planchette and answers your question, only if they trust you. People that do not believe in ghosts might not think this theory is true. Many mediums also think that nobody is really dead. Your soul has to be dead before you are. And just because your body is gone doesn't mean that your spirit is gone. And those spirits are answering our questions and helping us. But some might just be trying to hurt or confuse us.