Most hypnotic induction scripts use a countdown procedure such as "I am now going to count down from ten to one, and with each number you will become more and more relaxed, more at ease and when I reach the number one you will find yourself in a deep trance". Why is this form so common, and how does it work?
The reason count down inductions work is because the mind works primarily by metaphor. Metaphors are not just about words, we all have whole body metaphors, feelings and responses that are imbedded in our whole being.
When we are babies we have to learn some basic things about our world.
One of the very fundamental things all babies learn is the concept of 'up' and 'down'.
As infants we get lifted up and down.
Getting lifted up equals fun, attention, food and other active things.
Getting laid down equals quiet, being sung to, sleep.
Then we learn that the sun goes up and down.
When the sun goes down we go to sleep.
We all form unconscious associations between 'quiet, dark, down' and 'sleep'.
At school we learn that numbers go up and down. We form unconscious associations with numbers and link the progression of numbers to the up/down basic concept.
The whole notion of up/down is embedded in our worldview.
We talk about getting up, feeling up, (or feeling down) etc.
All of 'down' has to do with sleep, dark, quiet, sad, etc.
All of 'up' has to do with bright, alert, active, happy, etc.
So telling someone that you are going to count down causes them to expect to go quiet and relaxed, as when preparing for sleep. Add to that the use of the voice in ever deeper 'darker' tones, getting more quiet as you reach the lower numbers, invokes the entire metaphoric equivalence of 'down = sleep' and the body responds appropriately. Then add an image of going down stairs, floors in a building, an escalator etc., and you add another congruent metaphoric element. Then add to that suggestions that they relax their muscles, and the physical metaphor of 'relaxation = prepare for sleep' and the effect is even more powerful and invokes more automatic responses. Then suggest that they focus on their breathing, or the position of their hands, or some other physical aspect and you get dissociation. Put them all together and most people go into trance.
Whether you count 1 - 10 or 10 - 1 is irrelevant. Both can be considered going up or down, depending on how you choose to look at them. We are all comfortable with either direction. What is important is that you tell the client that the progression equals 'down'. That then invokes the metaphor equivalence.
You can actually use other lists to induce trance. Why stick to numbers? Why not list all the railway stations from north to south? Well, if you recite the names of the stations in an ever deepening voice and modulate the volume, that list would work just as well. It would also work if it was a long enough list of anything because the client's mind gets bored with a repetition of meaningless sounds and goes directly to dissociation. This is the basis of chants, mantras, religious rituals etc.
So, you do not need to use numbers, but numbers have the advantage of tapping into existing fundamental metaphors linked to preparation for sleep and relaxation.