四气五味

The four natures and five flavors are the core of Chinese materia medica theory. Every herb in the pharmacopeia can be initially described along two axes: its qi (here meaning its thermal property — warming or cooling) and its wei (its functional flavor). These categories are not subjective tasting impressions; they were arrived at empirically by generations of physicians observing how each herb actually behaves in the body. "Flavor" therefore designates not only the sensation on the tongue but, more importantly, a class of functional effects associated with that flavor.

Taken together, these two properties — together with channel tropism (归经) — constitute the three primary attributes of any Chinese herb. They are visible at the top of every herb page in this database.

The four natures are cold (寒, hán), cool (凉, liáng), warm (温, wēn), and hot (热, rè), with a fifth category, neutral (平, píng), added for herbs whose thermal effect is mild or balanced. Cold and cool herbs clear heat, drain fire, resolve toxicity, and cool the blood — they are used to treat heat patterns. Warm and hot herbs warm the middle, dissipate cold, restore yang, and tonify the fire — they are used to treat cold patterns. Cold and cool, and warm and hot, differ only in degree along a single axis: cold is stronger than cool, hot is stronger than warm. Neutral herbs are mild and are often used to harmonize a formula.

The nature of an herb is judged by the reaction it produces in the patient. An herb that resolves heat is classified as cold or cool; one that dispels cold is warm or hot. Coptis (黄连, Huáng Lián) is intensely bitter and cold, clearing Heart fire and treating mouth sores; aconite (附子, Fù Zǐ) is intensely acrid and hot, restoring yang and rescuing patients in collapse. The classical maxim governs use: "For cold, warm; for heat, cool."

The five flavors are acrid (辛, xīn), sweet (甘, gān), sour (酸, suān), bitter (苦, kǔ), and salty (咸, xián), with two further categories, bland (淡, dàn) and astringent (涩, sè), added by later writers. Each flavor names a class of functions:

Acrid herbs disperse and move — they release the exterior, move qi, and invigorate blood. Examples: ephedra (Má Huáng), cinnamon twig (Guì Zhī), fresh ginger (Shēng Jiāng).

Sweet herbs supplement, harmonize, and moderate — they tonify qi and blood, harmonize the actions of other herbs in a formula, and slow urgency or relieve pain. Examples: licorice (Gān Cǎo), ginseng (Rén Shēn), Chinese date (Dà Zǎo).

Sour herbs contract and bind — they astringe and stop leakage, treating diarrhea, sweating, bleeding, and frequent urination. Examples: schisandra (Wǔ Wèi Zǐ), white peony (Bái Sháo).

Bitter herbs drain, dry, and harden — they clear heat, redirect rebellious qi downward, dry dampness, purge the bowels, and "harden" yin (an idiom for restoring depleted yin against blazing fire). Examples: coptis (Huáng Lián), rhubarb (Dà Huáng), scutellaria (Huáng Qín).

Salty herbs soften and descend — they soften hardness, dissolve nodulation, and purge through the bowels. Examples: mirabilite (Máng Xiāo), seaweed (Hǎi Zǎo).

Bland herbs percolate dampness and promote urination, draining without harming the upright qi. Examples: poria (Fú Líng), Job's tears (Yì Yǐ Rén).

Astringent herbs share the function of the sour flavor, contracting and binding. Examples: dragon bone (Lóng Gǔ), Chinese gallnut (Wǔ Bèi Zǐ).

As with the four natures, "flavor" must not be reduced to literal taste. An herb classified as "sweet" need not taste sweet on the tongue — some bland-tasting tonifying herbs are still classified as sweet because their functional profile (supplementing, harmonizing, moderating) belongs to the sweet category.