Among the many principles of feng shui, the most widely known and most fundamental are mountain-behind-water-ahead and the sheltering of wind with the gathering of water. These two form a pair and have served as a great yardstick for judging good ground. Mountain-behind-water-ahead means, quite literally, a configuration that turns its back to a mountain and faces water in front. When a person settles with a sturdy mountain behind and clear water flowing before the eyes, such an arrangement has long been regarded as the most stable and livable of sites.
The mountain of this principle was seen not as mere background but as serving a real function. Winters on the Korean peninsula bring cold and fierce northwesterly seasonal winds, and when a mountain rises to the north or rear of a site, it blocks this cold wind and makes the place far warmer and more sheltered. Feng shui treated as important this way a mountain governs the wind and keeps energy from scattering, holding that when the rear is empty, both energy and livelihood scatter easily. To set a mountain at one's back was thus interpreted as softening the rough forces of nature to gain stability.
Sheltering wind and gathering water is a phrase that compresses the principle of mountain-behind-water-ahead still more sharply. Sheltering wind means harboring the wind, that is, mountain forms ringing all sides to temper cold and strong gusts and to keep the energy warm and even. Only a site where the wind does not pass freely but is well harbored, it was held, has settled energy in which people and household are at ease. Gathering water means obtaining water, a site where clear water flows or pools nearby so that domestic and farming water can be had with ease. In this single phrase, harbor the wind yet obtain the water, lies the image of the ideal site that feng shui pursued.
Regarding the gathering of water, a traditional way of thinking that likens water to fortune has also been handed down. Comparing the flow of water to the flow of wealth, a site where water gathers slowly and then curves gently away was held to be more auspicious than one where water drains straight off at speed. Water that departs in haste was thought to leave fortune unable to remain and scattered, whereas water that turns slowly as if embracing the site was thought to let gathered energy and fortune linger long. This shows well the traditional notion that received water not as a mere resource but as a symbol of vitality and abundance.
These principles of mountain-behind-water-ahead and the sheltering of wind with the gathering of water can actually be observed in the siting of many traditional Korean villages. A representative example is Hahoe Village in Andong, where the course of the Nakdong River winds around and embraces the village while a mountain ridge supports it from behind, often cited as a model of the auspicious form in which water circles slowly. Beyond this, old villages and historic houses were generally sited in mountain-behind-water-ahead positions with a mountain at the back and water and fields in front, which is interpreted as the natural meshing of feng shui thought with the conveniences of real life.
In the end, mountain-behind-water-ahead and the sheltering of wind with the gathering of water can be called principles that compress a traditional wisdom seeking to settle along the grain of nature, without going against its mountains, water, and wind. Blocking the wind to gain warmth and stability, and keeping water close to foster daily life and abundance, this way of thinking is said to hold, beyond the dimension of fortune, a way of living in which people and nature dwell together in harmony.
Looking a little more deeply into the gathering of water, one cannot leave out the concern with the mouth where water exits the site. People of old held that if the mouth by which water departs were left too widely open, the gathered energy and fortune would leak away with it, and so they deemed auspicious a site where the water mouth was suitably narrowed and screened by mountains or rocks. They also distinguished the shapes of water, calling foremost a stream that curves like a bow as if rounding and embracing the site, a form likened to the metal phase. This shows well the traditional eye that prized a flow which turns slowly as if gathered into an embrace over one in which the water turns its back on the site and runs straight off.