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The essentials of disease can be summarized in eight characters: Cold, Heat, Deficiency, Excess, Exterior, Interior, Yin, and Yang. Since pathological conditions do not fall outside this scope, the methods for syndrome differentiation also do not exceed it. To distinguish the Cold or Heat of a specific disease, one relies entirely on thirst or lack thereof, whether ingested water is consumed/digested, preference for hot or cold food and drink, presence of irritability or cold extremities (Jue Ni), length and color (red or pale) of urine, consistency of stool (loose or hard), and pulse rate (slow or rapid). For instance, if there is thirst with ability to consume fluids, preference for cold drinks/food, irritability, short red urine, hard stool, and a rapid pulse, this indicates Heat. Conversely, if there is no thirst, or false thirst without ability to consume fluids, preference for hot soups/drinks, cold hands and feet, clear and long urine, loose stool, and a slow pulse, this indicates Cold.

To distinguish the Deficiency or Excess of a specific disease, one relies entirely on presence or absence of sweating, presence or absence of chest/abdominal distension and pain, whether distension subsides or persists, whether pain rejects pressure or welcomes pressure, duration of the illness (new vs. old), constitution (robust vs. weak), and pulse quality (excess or deficient). For example, if there is no sweating during the illness, abdominal distension does not subside, pain rejects pressure, the illness is recent, the constitution is robust, and the pulse is excess and forceful, this indicates Excess. Conversely, if there is profuse sweating, abdominal distension temporarily subsides but returns, pain welcomes pressure and ceases upon pressing, the illness is chronic, the constitution is weak, and the pulse is deficient and weak, this indicates Deficiency.

To distinguish the Exterior or Interior location of a specific disease, one relies entirely on fever versus tidal fever (fever at fixed times), aversion to cold versus aversion to heat, headache versus abdominal pain, nasal congestion versus dry mouth, presence or absence of tongue coating, and pulse depth (floating or sunken). For instance, if there is fever with aversion to cold, headache, nasal congestion, no tongue coating, and a floating pulse, this indicates an Exterior syndrome. Conversely, if there is tidal fever with aversion to heat, abdominal pain, dry mouth, yellow or black tongue coating, and a sunken pulse, this indicates an Interior syndrome.

Regarding Yin and Yang in disease, they encompass the aforementioned six categories broadly. Heat belongs to Yang, Excess belongs to Yang, and Exterior location belongs to Yang; Cold belongs to Yin, Deficiency belongs to Yin, and Interior location belongs to Yin. When Cold pathogen lodges in the Exterior, it is Yin within Yang; when Heat pathogen enters the Interior, it is Yang within Yin. When Cold pathogen enters the Interior, it is Yin within Yin; when Heat pathogen reaches the Exterior, it is Yang within Yang. However, the distinction between True Yin and True Yang differs. For instance, if the pulse is rapid but forceless, deficiency fire flares intermittently, mouth and lips are dry, internal heat causes hard stool, and Qi rebels upward, this indicates insufficiency of True Yin. Conversely, if the pulse is large but forceless, limbs are fatigued, lips are pale and mouth feels harmonious, skin is cold, stool is loose, and food is not digested, this indicates insufficiency of True Yang.

The distinctions among Cold, Heat, Deficiency, Excess, Exterior, Interior, Yin, and Yang generally follow these principles. However, some cases present Heat syndromes yet prefer hot drinks due to "like attracting like." Some cases present Cold syndromes yet crave cold drinks but cannot swallow them, which is a sign of false thirst. Some cases present Heat syndromes yet have loose stools, known as diarrhea with accompanying Heat. Some cases present Cold syndromes yet have hard stools, named Yin Constipation (Yin Jie). Some cases present Heat syndromes yet have cold extremities, illustrating the principle that "the deeper the heat, the deeper the cold extremities; the milder the heat, the milder the cold extremities." Some cases present Cold syndromes yet exhibit irritability, desiring to sit or lie in mud or water, named Yin Restlessness (Yin Zao). Some cases with sweating manifest as Excess syndromes due to Heat pathogen transmitting to the Interior. Some cases without sweating manifest as Deficiency syndromes due to insufficiency of Body Fluids (Jin Ye). Some cases with aversion to cold manifest as Interior syndromes due to direct invasion by Cold. Some cases with aversion to heat and thirst manifest as Exterior syndromes because Warm-Heat diseases emerge from the Interior to the Exterior. These are the principles of Yin-Yang transformation and serve as the standard for treatment; therefore, early differentiation is particularly crucial.