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The tongue body is purple and lacks coating, indicating heat residing in the Yin aspect.

The tongue body is red and lacks coating, suggesting that pathogenic heat has just entered the Yin aspect, or it may be due to food stagnation preventing Stomach Qi from ascending, or due to worry and overthinking causing Qi stagnation and preventing Yang Qi from ascending.

If there is no coating on the tongue and the surface is smooth like a mirror, this indicates damage to both Stomach Yin and Stomach Yang. The villi within the intestines adhere to the walls, leading to symptoms of undigested food in stool (Wan Gu Bu Hua) and hunger without desire to eat. It may also be caused by tenacious phlegm stagnating in the stomach, preventing the formation of tongue coating, presenting similar signs. Pulse diagnosis must be consulted for comprehensive judgment.

In the former case of undigested food with Yin-Yang deficiency, the pulse will likely be fine and choppy (Xi Se). In the latter case of phlegm stagnation, the pulse will likely be surging, slippery, and large (Hong Hua Er Da).

The tongue body is dry and prickly, lacking coating. If it is purple and dry, it indicates heat damaging Yin fluids; if it is red and dry, it indicates Qi failing to transform into fluids. Pulse diagnosis must be consulted for comprehensive judgment.

A depression in the center of the tongue, appearing mottled or peeled, suggests dryness accumulation in the Stomach damaging Yin, or long-standing dryness accumulation in the cecum that remains unresolved.

A straight groove in the center of the tongue, resembling an imprint from the back of a knife, indicates deficiency of both Yin fluids and Yuan Qi.

Transverse cracks on the tongue body indicate a constitutional deficiency of Yin.

Cracks on the tongue resembling ice patterns are common manifestations of Yin deficiency in the elderly. This is rare in the young; its presence is inauspicious.

The anterior half of the tongue is smooth and lacks coating, while two fleshy nodules of the same color as the tongue flesh appear at the root. This is a sign of Yin deficiency consumptive disease (Yin Xu Lao Zheng).

The surface of the tongue lacks coating, but there is a coin-sized patch beneath the mucosa, colored yellow or white. This indicates insufficiency of Righteous Qi, blood deficiency, or phlegm condensation. Pulse diagnosis must be consulted for reference.

Round halos appearing on the tongue coating, divided into two or three colors, indicate internal binding of Dryness Metal and failure to pass dry feces; the condition is necessarily perilous.

Tongue coating appearing cyan-green indicates a fatal condition.

In summary, yellow coating is the normal/positive presentation, followed by white. Regardless of the disease, if treatment is appropriate, the coating will change from white to yellow, then recede, and finally regenerate as a new thin white coating. This is called a favorable pattern (Shun Xiang). Conversely, regardless of the disease, if treatment is inappropriate, the coating will change from yellow to white, from white to gray, from gray to black, and transform from a living coating to a dead coating. This is called an unfavorable pattern (Ni Xiang).

When Qi disperses, the coating disperses; when Qi condenses and knots, the coating condenses and knots. When Qi knots on one side, the coating also knots on one side. Therefore, in cases of Qi stagnation, the edge of the coating is neat, like the edge line of stone steps: coating inside the line, no coating outside the line, leaving only a red edge. If Qi relaxes and disperses, the coating becomes sparse from dense, losing its sharply cut, uniform edge. Thus, a coating with edges neat as if cut indicates Qi aggregation, associated with accumulation and depression.