How wide is your default horse stance? I see teachers recommending shoulder width when they are plainly standing much wider themselves. In my school we go to great pains to measure - here are two methods that we use. 1. We widen out our hand span thumb to little finger, and take our hands down to our feet, measuring with thumbs together, tips of little fingers to the centre of the foot (not inside or outside edge) 2. Feet together, turn toes out 45 degrees, then pivot on toes and end up with the outside edges parallel. Some further observations; I find one's imagined shoulder stance can depend on ego - those with a large ego have a wide stance, and those with self esteem problems stand much more narrow. Gender can play a role too, which made me wonder - should men use shoulder width and women hip width, or whichever is wider regardless of gender? I'd love to hear your thoughts.
I don't think that it's really all that important. Look at pictures of masters from the past doing forms and you will see that things like the width of the Horse Riding stance vary a great deal. My take (for what it's worth) is that you should do what feels comfortable and relaxed. The way we are taught the stance is to stand with our feet shoulder width apart, then to slide the left foot back half a foot length. Then to turn it to forty five degrees and 'sit down'. That is Single Whip posture, which is the most common use of the Horse Riding stance in our slow form.
I should think it depends a lot on which style of taijiquan you practice. I would imagine Chen stylists would have wider stances while Wu stylists would tend towards narrower stances. As a Hung Gar practitioner my horse stance is typically wider - the width is measured by standing with feet together, pushing heels out 45 degrees, then pushing toes out 45 degrees, then heels again. When I practice Yang style, my stance is the same width or slightly narrower (mostly because this is natural for me) and this does not seem at all unusual by Yang standards.
When both of your feet are - touching, you have very narrow horse stance. When you stand like this, you are weak to resistance against "foot sweet", but you are strong to resist against "leg spring". - moving apart, your resistance against "foot sweep" will increase, but your resistance against "leg spring" will decrease. - separate far apart, you have very wide horse stance. When you stand like this, you are strong to resistance against "foot sweet", but you are weak to resist against "leg spring". The horse stance is like a belt curve. There is only one proper width. Any width other than that will have to sacrifice resistance for either "foot sweep" or "leg spring".
I think some tai chi teachers like to play with measurements because that is all they know. Martial art practitioners talk about the transfer of weight between the legs instead of distance between the legs.
