Translated from Pertti Ruha’s blog HERE.
Seiza is written with two kanji (正座). The first is pronounced “sei” and means “correct, logical, true,” and if it stands on its own it is pronounced “tadashii.”
The character of “za” means “sitting position” and is written with an ideogram of two people sitting on a platform under a protective roof.
For Japanese seiza is, with the legs folded under the body, the proper and formal way of sitting on tatami mats indoors.
There are old images of Japanese warriors and noblemen sitting cross-legged, but during the Edo period (1600 – 1868) seiza was the position which applied to all well-mannered people on tatami mats.
There was an Edo period manuscript penned by Ogasawara Ryu, called Nihon no Reiho (Japanese etiquette; 日本之礼法).
We Westerners often find it difficult to sit with legs folded beneath us. We complain that the legs go to sleep, it hurts, etc. If it is any consolation, there were Japanese during the Edo period who complained about the same thing.
In Nihon no Reiho these complaints were dismissed and it was stated that they have not practiced enough. The author, Ogasawara Kiyonobu, advocates seiza because it shapes the body and spine into a natural posture, which leads to an alert mind. “Even if you just take your meals in seiza, it is good… by doing so, it creates a harmonious feeling and body posture is correct”
Seiza is a soothing position, but not for resting. Since seiza used for formal activities as described Ogasawara Kiyonobu it as “a loaded motion in stillness” (sei chu do; 静中動), as opposed to sitting in the full or half lotus position (stillness within stillness – sei chu sei; 静中静), and are used for meditation.
It emphasized that the eyes are naturally facing forward, eyes should be in the so-called “happo gan” (open look at all / eight directions – directed “beyond the mountains”). This means that the eye’s field of view is between directions at 9 am and 3 pm (9-12-3 eyes, battlefields gazing, etc.) and must not get stuck on any single object.
One should be alert, but also maintain a calm mind, balance the ability to “see” (ken; 見) and develop an ability to “sense” (kan; 觀).
“Kanken niyo no metsuke“(觀見によの目付) is a term that describes the warrior’s ability to see it visible and perceive the invisible in the environment.
Kiyonobu says that seiza probably grew naturally through experience, and it is a beautiful and active position, which is why it is currently used in Japanese martial arts and geido (art paths; 芸道).