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This classification method divides the East, West, South, and North into four principal directions (Si Zheng), and further divides the Southeast, Southwest, Northeast, and Northwest into four intermediate directions (Si Wei), totaling eight directions. Each direction has its governing climate qi: South wind is hot, East wind is warm, West wind is dry, and North wind is cold; Southeast wind is both warm and hot, Southwest wind is both dry and hot, Northeast wind is both cold and warm, and Northwest wind is both cold and dry. This represents the normal state of climate (Ping Qi). If the wind is excessive, it is called "Thief Wind" (Zeifeng, pathogenic wind). If Thief Wind is mild, the invasion in humans is also mild; if Thief Wind is severe, the invasion in humans is also severe.

The warmth, heat, cold, and dryness of the winds from the eight directions are distinguished solely by the East-West and South-North axes, existing regardless of the season. This differs from the Six Qi (Liuqi, Wind, Cold, Summer-heat, Dampness, Dryness, Fire) where Spring warmth, Summer heat, Autumn dryness, and Winter cold each govern a specific season.

Wei Qi (Defensive Qi) warms and nourishes the形体 (body form). As stated in the *Huangdi Neijing* (Yellow Emperor's Inner Canon), it "guards the exterior to maintain solidity"; as stated in the *Nan Jing* (Classic of Difficult Issues), it is the "Divine Spirit guarding against pathogens." When Wei Qi is solid and dense, various pathogens cannot invade; if there is even a slight gap, pathogens will attack. If the gap is in the head, the face is struck, resulting only in deviation of the mouth and eyes, while the hands and feet remain unharmed. If the gap is in the meridians of the hands, the arms are struck, resulting only in the inability to raise the wrists and arms, while the head and feet remain unharmed. If the gap is in the meridians of the feet, the hip joint is struck, resulting only in slow and heavy gait, while the head and hands remain unharmed. If the gap is on the left, the left side is affected and the right is unharmed; if the gap is on the right, the right side is affected and the left is unharmed.

If the pathogen strikes the Foot Shaoyin Kidney Meridian, the tongue becomes dry and speech is slurred (because the Shaoyin meridian winds around the root of the tongue); if it strikes the Hand Jueyin Pericardium Meridian, mental fatigue and frequent forgetfulness occur (because the Hand Jueyin Pericardium acts on behalf of the Heart Monarch); if it strikes the Hand Shaoyang Sanjiao (Triple Burner) Meridian, Sanjiao function becomes obstructed leading to frequent hiccups or choking sensations, and constipation occurs; if it strikes the Foot Taiyang Bladder Meridian, the bladder fails to clear turbidity, leading to cloudy urine, and even urinary retention (Longbi, difficulty or impossibility of urination) where urine cannot be expelled. This is because the Qi transformation of the bladder relies entirely on the permeating and draining action of Wei Qi. When Wei Qi is attacked by pathogenic wind and cannot perform this draining function, retention results. Such symptoms are too numerous to list; they all depend on the location of the gap where the pathogen enters. The *Huangdi Neijing* states: "Wherever pathogenic qi gathers, Zheng Qi (Upright Qi) must be deficient." This is analogous to chopping wood: an axe does not easily enter hard wood, but penetrates soft, brittle wood easily. Thus, this type of disease mostly occurs in people after middle age, because their Wei Qi has somewhat declined. In young and vigorous people, one in a hundred might suffer from it, because their Wei Qi is robust. Later generations, misunderstanding the meaning of Wei Qi, proposed the theory of "Left Blood, Right Qi," which is far off the mark. Others claim that blood deficiency generates internal wind, which is also not quite accurate. It should be known that the generation of internal wind is due to the deficiency of Wei Qi creating gaps, just as wind arises in empty valleys. It is not due to blood deficiency. Deficiency creates gaps, allowing pathogenic wind to enter; hence it is called "internal wind inducing external wind." Wei Qi originates from the Lower Jiao and is the root of wind generation, which is what the *Huangdi Neijing* refers to as the "Moving Qi between the Kidneys" (Shenjian Dongqi). The opening/closing, waking/sleeping, and entering/exiting of Wei Qi are distributed left and right. At the beginning of human formation, when the fetus first takes shape, its form resembles two shells, i.e., the two kidneys, wherein Wei Qi resides. Therefore, its movement during opening/closing and waking/sleeping must also be distributed left and right. This is a credible truth of inner physiology, merely unrecognized by mediocre physicians.

The root of the Moving Qi is indeed Kidney Qi, but it is specifically called "Moving Qi between the Kidneys" because it is the master of perception and movement, hence the addition of the character "Move" to denote it. If the Wei Qi on both sides is balanced, perception and movement are naturally crisp, healthy, and sharp. If the Wei Qi on one side is healthy while the other is diseased, perception and movement will inevitably fail to be as crisp, healthy, and sharp as usual. As the saying goes: "Many hands make light work, but one person struggles alone." This serves as a good analogy.

When wind strikes the left, the disease is on the left; when it strikes the right, the disease is on the right. However, deviation of the mouth corner is different: when striking the left, the mouth corner deviates to the right; when striking the right, the mouth corner deviates to the left. The reason is that when the left Wei Qi ceases to function, the meridians on the left become flaccid and relaxed, while the Wei Qi on the right functions exclusively, causing the meridians on the right to contract and spasm, thus pulling the mouth corner to the right (the meridians at the mouth corner are part of the Yangming Meridian encircling the lips, with one on each side). The case of striking the right follows this logic.