Yoi’ can mean different things depending on which kanji is used. In Karate, it can mean: ready; good; preparation.
Many karateka go into yoi by moving both feet, crossing arms low in front of the body (or making large arcs above their heads), then spreading their arms down wider than their bodies. I was taught to stand straight (musubi dachi), cross arms at chest level covering the solar plexus, then moving the left foot out shoulders-width and unfolding the arms down narrow, within the body’s width. Which way is correct? Is there a difference?
The first yoi is very expressive; ideal for performing kata. While dramatic, the first yoi takes two steps, keeping you on the embusen (line of attack). Folding the arms low on the body leaves your torso and head exposed to attack. Making large arcs above the head leaves the lower part of your body exposed to attack. Spreading your arms wider than your body leaves you exposed to frontal attack. Yoi as I was taught is better for self-defense. Crossing the arms at chest level makes it equally easy to block high or low, while covering vital organs and the solar plexus. Moving just the left foot out takes you off the attack line. Bringing the arms down narrow within the body’s width offers more protection from attack. Like the front bumper of a car, the arms can absorb some impact from a forward attack.
A student once asked me how wide (or narrow) the arms should be. I told him, “The rule of thumb is to extend the thumbs from your fists and they touch.” He smiled and said, “So the rule of thumb is the rule of thumbs.” Yep. He then thought if I wrote this blog entry it should be called ‘The Thumb - Going My Way’ (a play on words since ‘Dō’ means ‘The Way’).
So, which yoi is correct? Which yoi is proper? The correct yoi is the one your sensei requires at your dojo. The proper yoi is either one, although you can probably guess my preference.