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The *Yin Yang Ying Xiang Lun* (Treatise on Yin and Yang Corresponding to Images) states: The accumulation of Yang Qi (vital energy) forms Heaven, and the accumulation of Yin Qi forms Earth. Yin is quiet, while Yang is restless; Yang generates, Yin grows; Yang destroys, Yin stores.
Yang transforms into Qi, while Yin takes form. Yang manifests as Qi, and Yin manifests as Flavor. Flavor nourishes Form, Form relies on Qi, Qi transforms into Essence, and Essence is generated through transformation; Essence consumes Qi, and Form consumes Flavor, transformation generates Essence, and Qi generates Form. Excessive Flavor damages Form, excessive Qi damages Essence, Essence can transform into Qi, but Qi is damaged by excessive Flavor. Yin flavors exit through the lower orifices, while Yang Qi exits through the upper orifices. Clear Yang disperses into the Cou Li (interstitial spaces of skin and muscle), while Turbid Yin flows into the Zang organs (solid organs); Clear Yang fills the four limbs, while Turbid Yin returns to the Fu organs (hollow organs). Flavors that are strong belong to Yin, while those that are weak belong to Yang within Yin; Qi that is strong belongs to Yang, while that which is weak belongs to Yin within Yang. Strong flavors have a purgative effect, while weak flavors have a unblocking effect; weak Qi has a dispersing and releasing effect, while strong Qi has a heating effect. Pungent and Sweet flavors have a dispersing action and belong to Yang; Sour and Bitter flavors have an inducing-vomiting or purgative action and belong to Yin; Salty flavor has an inducing-vomiting or purgative action and belongs to Yin; Bland flavor has a leaching and draining action and belongs to Yang. These six properties either astringe or disperse, either relax or tense, either moisten or dry, either soften or harden. They are utilized according to their benefits to harmonize Qi and restore balance.

Zhang Yuansu stated: The clearest of the clear disperses into the Cou Li; the turbid part of the clear fills the four limbs. The most turbid of the turbid returns to the Fu organs; the clear part of the turbid flows into the Zang organs. Fuzi (Aconiti Lateralis Radix Preparata) has strong Qi and belongs to Yang within Yang; Dahuang (Rhei Radix et Rhizoma) has strong Flavor and belongs to Yin within Yin. Fuling (Poria) has weak Qi and belongs to Yin within Yang, thus it promotes urination and enters the Hand Taiyang channel, remaining close to the nature of Yang; Mahuang (Ephedrae Herba) has weak Flavor and belongs to Yang within Yin, thus it induces sweating and enters the Hand Taiyin channel, remaining close to the nature of Yin. All things with the same Qi must possess various flavors, and all things with the same flavor must possess various Qis. Because Qi and Flavor vary in strength, their therapeutic effects differ.

Li Gao stated: Weak flavors promote unblocking, such as Sour, Bitter, Salty, and Neutral natures. Strong flavors promote purging, such as Salty, Bitter, Sour, and Cold natures. Strong Qi causes heat, such as Pungent, Sweet, Warm, and Hot natures. Weak Qi promotes leaching and draining, such as Sweet, Bland, Neutral, and Cool natures. "Leaching" refers to slight perspiration, and "draining" refers to promoting urination.

Wang Haogu stated: After Heaven and Earth separated, only the Five Qi generated all things. Once the positions of the Five Qi were established, the Five Flavors arose. Thus, it is said that Qi generates living things, while Flavor completes them. What is born from odd numbers becomes even upon completion, and what is born from even numbers becomes odd upon completion. Cold Qi is firm, so its flavor can be used to soften; Heat Qi is soft, so its flavor can be used to harden; Wind Qi is dispersing, so its flavor can be used to astringe; Dryness Qi is collecting, so its flavor can be used to disperse. Earth is generated by the Harmonious Qi, which harmonizes everything, so its flavor can be used to relax. Firm Qi strengthens, so Bitter flavor can nourish Qi. Soft pulses indicate harmony, so Salty flavor can nourish vessels. Collecting bones indicate strength, so Sour flavor can nourish bones. Dispersing sinews prevent spasms, so Pungent flavor can nourish sinews. Relaxed muscles prevent stagnation, so Sweet flavor can nourish flesh. One must first harden before one can soften; one must first collect before one can disperse. To relax, use Sweet flavor; if relaxation is not desired, do not use it. Do not overuse it, for excess also causes disease. Ancient practitioners of health preservation and disease treatment must first understand this principle; otherwise, few could cure others' illnesses.

Li Gao stated: Medicines have Warm, Cool, Cold, and Hot Qis, and Pungent, Sweet, Bland, Sour, Bitter, and Salty flavors. There are interactions of Ascending, Descending, Floating, and Sinking, and differences in Strength, Weakness, Yin, and Yang. Within a single herb, both Qi and Flavor are present; within a single medicine, its therapeutic nature is complete.
Some have the same Qi but different flavors, some have the same flavor but different Qis. Qi resembles Heaven: Warm and Hot are Heaven's Yang; Cool and Cold are Heaven's Yin. Heaven has Yin and Yang, Wind, Cold, Summer-heat, Dampness, Dryness, and Fire, along with Three Yin and Three Yang, which are upheld by Heaven. Flavor resembles Earth: Pungent, Sweet, and Bland are Earth's Yang; Sour, Bitter, and Salty are Earth's Yin; Earth has Yin and Yang, Metal, Wood, Water, Fire, and Earth, corresponding to Generation, Growth, Transformation, Harvest, and Storage, which are responded to by Earth. Those with weak Qi and Flavor are light and clear, forming images, belonging to Heaven and亲近 the upper; those with strong Qi and Flavor are heavy and turbid, forming shapes, belonging to Earth and亲近 the lower.

Kou Zongshi stated: Materia Medica flavors are five, and Qi types are four. However, within one flavor, there may be four Qis; for example, among Pungent flavors, Shigao (Gypsum Fibrosum) is Cold, Guizhi (Cinnamomi Ramulus) and Fuzi are Hot, Banxia (Pinelliae Rhizoma) is Warm, and Bohe (Menthae Haplocalycis Herba) is Cool. Qi belongs to Heaven: Warm and Hot are Heaven's Yang, Cold and Cool are Heaven's Yin; Yang ascends, Yin descends. Flavor belongs to Earth: Pungent, Sweet, and Bland are Earth's Yang, Sour, Bitter, and Salty are Earth's Yin; Yang floats, Yin sinks. Some medicines primarily utilize Qi, some primarily utilize Flavor, some utilize both Qi and Flavor, some act via Qi first then Flavor, and some via Flavor first then Qi. There are herbs with one flavor, three flavors; with one Qi type, two Qi types. Raw and processed forms may have different Qi and Flavor; roots and shoots may have different Qi and Flavor. If Warm predominates, it becomes Hot; if Cool predominates, it becomes Cold; if Cold and Hot are equal, it becomes Warm. If Hot predominates and Cold is scarce, the Cold nature is suppressed and does not manifest as Cold; if Cold predominates and Hot is scarce, the Hot nature is suppressed and does not manifest as Hot. One cannot apply a uniform rule. If Cold and Hot are equal, taking it during the day follows the Hot category and ascends, while taking it at night follows the Cold category and descends; sunny days follow Heat, cloudy days follow Cold. Changes are diverse like this. Moreover, the Four Seasons and Six Positions differ, and the Five Movements and Six Qi vary. How can one prescribe lightly?

The *Liu Jie Zang Xiang Lun* (Treatise on the Six Nodes and Viscera Manifestations) says: Heaven feeds humans with Five Qi, and Earth feeds humans with Five Flavors. Five Qi enter through the nose and store in the Heart and Lung, causing the complexion to become bright and the voice to resonate clearly. Five Flavors enter the mouth and store in the intestines and stomach; the stored flavors nourish the Five Qi. When Qi is harmonious, life arises; when fluids and essence combine, Spirit naturally emerges. It also states: For deficiency of Form, warm it with Qi; for deficiency of Essence, tonify it with Flavor.

Wang Bing stated: Among the Five Qi, Dryness Qi approaches the Liver, Scorched Qi approaches the Heart, Fragrant Qi approaches the Spleen, Fishy Qi approaches the Lung, and Putrid Qi approaches the Kidney. The Heart governs blood color, and the Lung governs sound, so Qi stores in the Heart and Lung, making color bright and sound resonant. Qi is the mother of Water, so Flavor stores in the intestines and stomach to nourish the Five Qi. Sun Simiao stated: Essence is nourished by Qi, and Qi nourishes Essence to brighten the complexion; Form is nourished by Flavor, and Flavor nourishes Form to generate strength. Essence becomes spiritual by following the Five Qi, and Form is completed by receiving the Five Flavors. If the consumed Qi is contrary, it damages Essence; if the consumed Flavor is unbalanced, it harms Form. Therefore, sages first used dietary taboos to preserve life, and later formulated drugs to prevent death, using the warming and tonifying properties of Qi and Flavor to preserve Essence and Form.