四诊者，望闻问切也。望以辨色，闻以辨声，问以辨证，切以辨脉。盖人禀气血以生，气血不和而为病，
有诸内者，必形诸外，但病变多端，其脉其证皆有真假，差之毫厘，失之千里，故圣人立法，必以四端互相
参合，方无错误，如《素问·疏五过论》、《征四失论》，谆切告诫，而俗学不明此理，妄意揣度，虚言矜夸，
谓切脉即能知病，欺人自欺，其害实甚。又如《难经》言∶假令得肝脉，其外证善洁、面青、善怒，其内证脐
左有动气，按之牢若痛，其病四肢满闭，淋溲便难，转筋，有是者肝也，无是者非也。此言诊得弦急之脉为肝
脉，必有肝脏之证，如面青、善怒等，方为肝病，如无肝证，即非肝病，各脏皆然，是故一脉所主，病有多
端，一病所现，亦有多脉，必当脉证互相印合，方能知其病由，故四诊之道，缺一不可，经文已详悉矣。惟辨
舌苔之法，未曾论及，止有《灵枢·师传篇》云∶
脾者主为卫，使之迎粮，视唇舌好恶，以知吉凶；《热病篇》言∶肺热病，舌上黄而已。盖脾主肌肉，卫者，
肌肉也，唇舌为肌肉之本，故视之可验病之吉凶也。若夫强弱寿夭之形，及一切病状，尤当于禀赋疾病诸门合
参，以明其理。本门最详者脉也，脉为气血流行之象，而有升降出入，故当与营卫经络、阴阳脏腑诸门同观。
必得悟其神理，指下方能明其为和为病、为虚、为实。古人论脉云∶吾心之所解，口莫能宣。此神理必须心悟，
非言语所能传。能明其脉，则证之真假自见；能辨其证，则脉之虚实自明。所谓真者，脉证相合，虚实显然也；
所谓假者，脉证不合，实病似虚、虚病似实也。真者易辨，假者难辨，不辨其假而误治之，杀人于反掌间，
可不畏哉！可不慎哉！
The Four Diagnostic Methods refer to inspection (Wang), auscultation and olfaction (Wen), inquiry (Wen), and palpation (Qie). Inspection is used to distinguish colors, auscultation and olfaction are used to distinguish sounds and smells, inquiry is used to distinguish syndromes, and palpation is used to distinguish pulses. Since humans are born with Qi and Blood, disease arises when Qi and Blood are disharmonious. Internal pathology must manifest externally. However, pathological changes are manifold, and both pulses and syndromes may present as true or false. A discrepancy of a hair's breadth can lead to an error of a thousand miles. Therefore, the Sages established laws requiring the mutual cross-reference of these four methods to avoid errors. As repeatedly and earnestly warned in *Suwen: Shu Wu Gu Lun* (Plain Questions: Discourse on Avoiding Five Negligences) and *Suwen: Zheng Si Shi Lun* (Plain Questions: Discourse on Identifying Four Failures), lay practitioners who fail to understand this principle often speculate rashly, boast with empty words, and claim that pulse diagnosis alone suffices to know the disease. This deceives others and oneself, causing great harm.
Furthermore, *Nan Jing* states: Suppose one obtains the Liver Pulse. Its external manifestations include a preference for cleanliness, a bluish complexion, and irritability. Its internal manifestations include pulsating Qi at the left side of the umbilicus, which feels firm and painful upon pressure. Its diseases include fullness and obstruction of the four limbs, dribbling or difficult urination, difficult defecation, and tendon spasms. If these symptoms are present, it is a Liver disease; if absent, it is not. This indicates that obtaining a wiry and rapid pulse identified as the Liver Pulse requires accompanying Liver organ syndromes, such as a bluish complexion and irritability, to confirm Liver disease. Without Liver syndromes, it is not Liver disease. The same applies to other Zang organs. Thus, one pulse type may correspond to multiple diseases, and one disease may present with multiple pulses. One must mutually verify pulses and syndromes to ascertain the origin of the disease. Hence, the Four Diagnostic Methods are indispensable, as detailed in the classics.
However, the method of distinguishing tongue coating is not extensively discussed here. Only *Lingshu: Shichuan Pian* (Spiritual Pivot: Chapter on Teacher's Transmission) states: "The Spleen acts as the guard, facilitating the reception of grain. By observing the condition of the lips and tongue, one can discern auspicious or inauspicious outcomes." *Re Bing Pian* (Chapter on Heat Diseases) states: "In Lung Heat Disease, the tongue coating is yellow." This is because the Spleen governs muscles, Wei Qi (Defensive Qi) resides in the muscles, and the lips and tongue are the roots of the muscles; thus, observing them verifies the prognosis. Regarding physical strength, longevity, and all pathological conditions, one must particularly integrate findings from constitutions (Bingfu) and various disease categories to clarify the principles. Among these, pulse diagnosis is most detailed. Pulses reflect the circulation of Qi and Blood, involving ascending, descending, exiting, and entering movements. Therefore, they should be viewed in conjunction with Ying and Wei (Nutritive and Defensive Qi), meridians, Yin and Yang, and Zang-Fang organs. One must comprehend their subtle principles so that under the fingers, one can clearly distinguish between harmony and disease, deficiency and excess. Ancient masters said regarding pulse diagnosis: "What my mind understands, my mouth cannot fully express." These subtle principles require mental comprehension and cannot be transmitted merely through words. If one understands the pulses, the truth or falsity of syndromes becomes apparent; if one distinguishes the syndromes, the deficiency or excess of the pulses becomes clear. What is termed "True" is when pulses and syndromes coincide, making deficiency and excess obvious. What is termed "False" is when pulses and syndromes do not coincide, where Excess diseases mimic Deficiency, and Deficiency diseases mimic Excess. True conditions are easy to distinguish; False conditions are difficult. Failing to distinguish the false and treating erroneously can kill someone in the blink of an eye. Can one not revere this? Can one not be cautious!