People of average intelligence (unless there is some form of organic brain damage) can be hypnotised in most cases, if they are willing. The depth of hypnosis varies with a person’s ability to respond. If you are not a naturally responsive subject, you can improve your receptivity to hypnosis with practice.
This question alone, however, is an example of the misunderstanding of what hypnosis is and how it works. Hypnosis or being in a hypnotic state is just as natural as breathing and sleeping. You may even be in a hypnotic state as you are reading this.
Any time we are in what is called ‘the zone’ or spaced out or daydreaming we are referring to the same thing, being out of the state of conscious, analytical thinking and entering what is a light hypnotic state. We drift in and out of this ‘light trance’ state all day, every day.
There are four levels of brain wave activity: Beta, Alpha, Theta and Delta. Once we leave the total awareness, conscious, analytical state of mind (Beta) we drift into the Alpha state. This is considered a light level hypnotic state though a lot of change can be directed in this state. This is also why some hypnosis clients may think they were not hypnotised, because it was a lighter level and not what they expected hypnosis to be. Though these same people welcome the positive changes they achieve from this process.
Theta is the state of mind when we are dreaming when asleep, though still conscious as we are aware of many of our dreams.
Delta is to to be unconscious.
With this simple understanding, it may seem that all people can be hypnotised. Well, not quite. Though the number varies a bit, it is reported that people with an IQ below 70 will not respond to hypnosis and anyone who is too drunk would not be a good candidate either. Therefore it is safe to say that almost all people, especially anyone who comes to a hypnosis session on their own is capable of being hypnotised.
There is definitely one factor to prevent the hypnotic process from happening though and that is you! If you do not want to be hypnotised, then you won’t.