The problem is that what you are trying define is intangible. You can feel or touch it. It is a state of mind that you may or may not be aware of. We are actually in this naturally several times a day. The problem is that if you ask a bunch of experts for a definition, you will get a bunch of definitions. Roy Hunter posts the FAQ in alt. hypnosis.
Even as we enter the 21st Century, opinions still vary on the exact definition of this natural state of mind. First of all, contrary to what many commonly believe, hypnosis is NOT a "sleep" state even though a person in hypnosis may appear to be sleeping. James Braid, a 19th Century English physician, gave us the name "hypnotism" because the people he mesmerized appeared to be asleep. Within a few months he tried to change the name that he coined, but instead found that hypnotism is here to stay.
Some people assume that a hypnotized person is asleep, especially because one who goes into a very deep trance can sometimes have partial amnesia. I prefer the way my late mentor, Charles Tebbetts, defined hypnosis, so let me quote his exact words as written in MIRACLES ON DEMAND (which is currently out of print): "There is no legal definition of hypnosis. Webster's dictionary describes it incorrectly as an artificially induced sleep, but it is actually a natural state of mind and induced normally in everyday living much more often than it is induced artificially. Every time we become engrossed in a novel or a motion picture, we are in a natural hypnotic trance (p. 211-212)." He also taught that all hypnosis is self-hypnosis, and many in the hypnotherapy profession believe likewise.
I totally agree with the above, and I also believe that THE POWER IS IN THE MIND OF THE PERSON BEING HYPNOTIZED. So, in reality, the hypnotherapist acts like a guide who facilitates the hypnotic process. Myron Teitelbaum, M.D., author of HYPNOSIS INDUCTION TECHNICS, came to the same conclusion - as is evidenced by what he wrote in the last part of Chapter 3: "The hypnotist is merely the guide who directs and leads the subject into the trance (page 18)." Yet even today there are debates over whether this is true. (Simply by reading the postings on this newsgroup, you may soon discover that people are still debating over who has the power!)
In my opinion, the most accurate way of defining hypnosis is to simply call it "guided meditation." Since many of us enter a meditative or "trance" state while listening to music, watching TV, listening to a good speaker or a good sermon at church, or even while reading, you could say that the hypnotist does not even have to be a live person. So if hypnosis were ever outlawed, it would be virtually impossible to enforce, because we would have to stop the freedom of speech and freedom of press; and we would have to outlaw TV, music, sermons, political speeches, etc.!
The above being said, a personal friend of mine (and a well-known expert in hypnotherapy) does NOT believe that all hypnosis is self-hypnosis...as stated on his web site. He states, "Hypnosis is a focusing of attention and resonation with the unconscious mind. It is fairly easy to do this without the cooperation of another person's conscious mind." He is not alone in this opinion, nor am I alone in my opposite viewpoint. While I respect my friend's accomplishments in the field of hypnotherapy, I respectfully disagree with him and retain my personal opinion. No matter how deep one goes into the hypnotic state, if the hypnotized person BELIEVES that all hypnosis is self-hypnosis, he/she will be more easily able to reject (or modify) any unwanted suggestions. However, if one believes that he/she is under the total control of the hypnotist, might he/she be more likely to respond according to that belief?