1. Yin and Yang

1. Yin and Yang

Yin and Yang are the first of the Eight Principles. All disease characteristics can broadly be divided into two major categories: Yin syndromes and Yang syndromes. No matter how complex or varied the clinical manifestations may be, they ultimately fall into one of two categories: excessive Yin and deficient Yang, or excessive Yang and deficient Yin. When conducting syndrome differentiation, we must first distinguish between Yin and Yang, and then further differentiate between Exterior and Interior, Cold and Heat, and Deficiency and Excess, so as to achieve clear layering and accurate diagnosis. The “Plain Questions” states: “Yin and Yang are the way of heaven and earth, the guiding principles of all things, the parents of change, the origin of life and death, the abode of the divine, and the foundation of healing. One must seek the root cause when treating illness.” The “Plain Questions” also says: “A skilled diagnostician first distinguishes Yin from Yang by observing color and taking the pulse.” Zhang Jingyue further stated: “In all pulse diagnosis and treatment, one must first examine Yin and Yang, for they are the fundamental principles of medical practice. Without Yin and Yang, there can be no proper treatment. Though medical practice may seem complex, it can be summed up in one word: Yin and Yang.” From this, we can see the crucial role of Yin and Yang in syndrome differentiation and treatment.

(1) Basic Manifestations of Yin and Yang Syndromes

Basic manifestations of Yin syndromes: listlessness, dull complexion, vacant gaze, weak voice, feeling cold with cold limbs, slow movements, poor appetite and little drinking, clear and long urination, loose stools, thin white tongue coating, and a fine, slow, and weak pulse. In short, any condition involving decline in bodily functions, nutritional deficiency, or organ degeneration generally falls under the category of Yin syndromes.

Basic manifestations of Yang syndromes: high spirits, flushed face, bloodshot eyes, loud voice, aversion to heat and preference for coolness, restlessness and hyperactivity, thirst and rapid breathing, short and reddish urine, hard and dry stools, thick yellow and dry tongue coating, and a rapid, strong, and forceful pulse. In short, any condition involving heightened bodily functions, adequate nutrition, or new organic lesions in the organs generally falls under the category of Yang syndromes.

However, the Yang and Yin syndromes encountered in clinical practice are rarely as typical as the examples above. More often, they present as “Yin contains Yang” or “Yang contains Yin,” forming complex syndromes such as “Exterior and Interior combined,” “Cold and Heat intermingled,” or “Deficiency and Excess seen together.” Some patients exhibit Yin deficiency with Yang excess, others have excessive Yin and deficient Yang, some suffer from both Yin and Yang deficiency, while others experience both Yin and Yang excess. Given the complexity of Yin and Yang clinical manifestations, it is essential during clinical differentiation to clearly identify the true nature of Yin and Yang, their mutual transformation, and which is predominant, in order to provide an accurate basis for treatment.

(2) Yin Deficiency and Yang Deficiency

The kidneys are the foundation of innate vitality and the source of true Yin and true Yang. The right kidney is the “Mingmen,” housing true Yang; the left kidney is the “Kidney,” housing true Yin. If true Yin is insufficient, internal fire rises, causing red cheeks and rosy lips, dry mouth and throat, bone-steaming heat, five-heart vexation, night sweats and nocturnal emissions, a red tongue with little coating, and a fine, rapid, and weak pulse. If true Yang is insufficient, the complexion becomes pale, there is spontaneous sweating and fatigue, loss of appetite, shortness of breath and reluctance to speak, feeling cold and afraid of cold, abdominal distension and loose stools, diarrhea at dawn, impotence and nocturnal emissions, heavy and sluggish legs, a swollen tongue with tooth marks, a thin white coating, and a large, weak pulse, especially a weak pulse at the cun position.

(3) Loss of Yin and Loss of Yang

The “Plain Questions” states: “When Yin and Yang are severed, vital energy disperses.” Loss of Yin and loss of Yang are signs that Yin and Yang are about to be completely severed, representing dangerous syndromes that appear during the progression of disease and marking the inevitable path toward death. In such situations, it is crucial to make an accurate diagnosis and take immediate, decisive action to implement the most rapid and effective rescue measures in order to turn danger into safety.

Clinical manifestations of loss of Yin include chest tightness and shortness of breath, warm hands and feet, hot skin, thirst for cold drinks, salty and non-sticky sweat, a red tongue with no moisture, and a fine, rapid, and weak pulse.

Clinical manifestations of loss of Yang include a pale face, cold limbs, feeling cold and afraid of cold, spontaneous sweating, a pale and swollen tongue, and a floating, hollow, or extremely weak pulse.

Loss of Yin represents the extreme stage of Yin deficiency syndrome. According to the principle that “Yin deficiency generates internal heat,” loss of Yin syndrome still retains symptoms similar to “internal heat,” such as warm hands and feet and hot skin. However, as loss of Yin progresses, these “internal heat” symptoms may disappear due to the principle that “isolated Yin does not generate heat” and “isolated Yang does not grow.” Loss of Yang, on the other hand, can quickly lead to loss of Yin syndrome, followed by death. All fatal cases end with loss of Yang, meaning that loss of Yin precedes loss of Yang, and the two often occur simultaneously. The “Plain Questions” states: “Yang qi is like heaven and the sun; if it loses its place, lifespan is shortened and vitality is diminished.” Thus, among loss of Yin and loss of Yang, loss of Yin is the critical sign, and the progression of loss of Yin inevitably leads to loss of Yang; however, there are also cases where loss of Yang occurs first, followed immediately by loss of Yin, and sometimes both loss of Yin and loss of Yang occur concurrently.