四难曰∶脉有阴阳之法，何谓也？
然∶呼出心与肺，吸入肾与肝，呼吸之间，脾受谷味也，其
脉在中。
此言脉之阴阳虽在于尺寸，其阴阳之气，又在浮沉。如心肺居膈上，阳也，呼出必由之，肾
肝居膈下，阴也，吸入必归之。脾受谷味，为生脉之原而在中，而呼出吸入，无不因之，故诊
脉之法，浮取乎心肺，沉取乎肾肝，而中应乎脾胃也。
按∶经言呼出者，非气自心肺而出也，为肾肝在膈下，其气因呼而上至心、至肺，故呼出心
与肺也。心肺在膈上，其气随吸而入至肾、至肝，故吸入肾与肝也。夫呼者因阴出，吸者随阳
入，其呼吸阴阳，相随上下，经历五脏之间，乃脾胃受谷气以涵养之也，故言其脉在中。读此
节不得刻舟求剑，谓呼出之气为阳，吸入之气为阴也。
浮者阳也，沉者阴也，故曰阴阳也。
按之不足，举之有余曰浮，浮为阳者，象火而炎上也；按之有余，举之不足曰沉，沉为阴者，
象水而润下也。
心肺俱浮，何以别之？
然∶浮而大散者，心也；浮而短涩者，肺也。肾肝俱沉，何以别之？
然∶牢而长者，肝也；按之濡，举指来实者，肾也；脾者中州，故其脉在中。是阴阳之法也。
浮大无力，按之散而欲去者，名曰散；浮细而迟，往来蹇滞不前者，名曰涩。沉而有力，实
大弦强，按之但觉坚极而不移者，名曰牢；大而长微弦，按之隐指 然，中取、沉取皆有力
者，名曰实。心肺俱俘，何以别之？盖心属火，故其象浮而大散；肺属金，故其象浮而短涩。
肾肝俱沉，何以别之？盖肝属木，故其象牢而长；肾属水，故其象举指按之来实，水体外柔而
内刚也。脾属土在中，旺于四季，主养四脏，其脉来从容和缓，不沉不浮，故曰其脉在中也。
脉有一阴一阳，一阴二阳，一阴三阳；有一阳一阴，一阳二阴，一阳三阴。如此之言，寸口有
六脉俱动邪？
然∶此言者，非有六脉俱动也，谓浮沉长短滑涩
也。浮者阳也，滑者阳也，长者阳也，沉者阴也，短者阴也，涩者阴也。所谓一阴一阳者，谓脉来
沉而滑也，一阴二阳者，谓脉来沉滑而长也。一阴三阳者，谓脉来浮滑而长，时一沉也；所谓一阳
一阴者，谓脉来浮而涩也，一阳二阴者，谓脉来长而沉涩也，一阳三阴者，谓脉来沉涩而短，时一
浮也。各以其经所在，名病逆顺也。
过于本位谓之长，不及本位谓之短，按之往来流利，辗转替替然，谓之滑也。前引五脏之脉，
以应五行，此又引三阴三阳之脉，以应六气。其浮滑长，三阳也；沉短涩，三阴也。而于三部
中察此六脉，即可知阴阳盛衰之机。盖阴阳之脉不单至，惟其不单至，故有此六脉相兼而见，惟其
相兼，故有一阴一阳，一阳一阴之不同也。此别阴阳虚实之法。再参春夏秋冬，观其六脉之变，则
庶乎可知病之逆顺矣。
按∶徐氏曰∶此节言六脉互见之象也，此但举其例而言，亦互相错综，非一定如此也。其经，
手足三阴三阳也；逆顺，如心脉宜浮，肾脉宜沉，则为顺；若心脉反沉，肾脉反浮，则为逆。此又
见脉无定体，因经而定顺逆也。然脉之浮沉，或可相兼，滑涩长短，不得并见，亦当晓也。
第四难问道：脉象有区分阴阳的方法，这是什么意思呢？
回答说：呼气时，气由心与肺发出；吸气时，气归于肾与肝。在呼吸之间，脾脏接受水谷的精微之气，其脉象位于中部。
这段文字说明，脉象的阴阳虽然体现在寸口脉的尺部和寸部，但阴阳之气的表现又在于脉位的浮与沉。例如，心与肺位于膈肌之上，属阳，呼气时气必由此而出；肾与肝位于膈肌之下，属阴，吸气时气必由此而归。脾脏接受水谷精微，是生成脉气的本源，位于中焦，而呼气和吸气无不依赖于此，所以诊脉的方法，轻取（浮取）以候心与肺，重按（沉取）以候肾与肝，中取以候脾胃。
按语：经文所说的“呼出”，并非指气直接从心肺排出体外，而是因为肾与肝位于膈下，其气随着呼气向上运行至心、至肺，所以说“呼出心与肺”。心与肺位于膈上，其气随着吸气向下进入至肾、至肝，所以说“吸入肾与肝”。呼气是因阴气外出，吸气是随阳气内入，呼吸过程中的阴阳二气，相随上下，经历五脏之间，这是脾胃受纳谷气来涵养它们的结果，所以说脉象在中。读这一节不能拘泥刻板地认为，呼出的气就是阳，吸入的气就是阴。
轻按感觉不足，重举感觉有余的称为浮，浮脉属阳，像火一样炎上；重按感觉有余，轻举感觉不足的称为沉，沉脉属阴，像水一样润下。
回答说：脉象浮大而散漫的，是心脉；脉象浮而短促涩滞的，是肺脉。肾与肝的脉象都沉，如何区别它们呢？
回答说：脉象牢靠而长的，是肝脉；重按时柔软，轻抬手指时感觉充实有力的，是肾脉；脾脏位于中州（中焦），所以它的脉象位于中部。这就是区分阴阳的方法。
补充解释：脉象浮大无力，重按时散漫且似要离去的样子，称为散脉；脉象浮细而迟，往来艰难阻滞不前，称为涩脉。脉象沉而有力，实大弦强，重按时只觉得坚硬至极而不移动，称为牢脉；脉象大而长略带弦象，重按时隐指坚实，中取和沉取都有力的，称为实脉。心与肺的脉象都浮，如何区别呢？因为心属火，所以其脉象表现为浮而大散；肺属金，所以其脉象表现为浮而短涩。肾与肝的脉象都沉，如何区别呢？因为肝属木，所以其脉象表现为牢而长；肾属水，所以其脉象表现为轻抬手指重按时感觉充实，这是因为水性外柔内刚。脾属土，位居中央，旺于四季，主滋养其他四脏，其脉象来去从容和缓，不沉不浮，所以说它的脉象在中。
脉象有一种阴一种阳，一种阴两种阳，一种阴三种阳；还有一种阳一种阴，一种阳两种阴，一种阳三种阴。这样的说法，是指寸口六部脉同时跳动吗？
回答说：这里说的，并不是指六部脉同时跳动，而是指浮、沉、长、短、滑、涩这六种脉象。浮脉属阳，滑脉属阳，长脉属阳；沉脉属阴，短脉属阴，涩脉属阴。所谓“一阴一阳”，是指脉象来势沉而滑；“一阴二阳”，是指脉象来势沉、滑而长。“一阴三阳”，是指脉象来势浮、滑、长，偶尔出现一次沉象；所谓“一阳一阴”，是指脉象来势浮而涩；“一阳二阴”，是指脉象来势长、沉而涩；“一阳三阴”，是指脉象来势沉、涩而短，偶尔出现一次浮象。根据这些脉象所在的经络部位，来判断疾病的逆顺。
超过本位延伸的称为长，不及本位的称为短；重按时往来流利，辗转替替然，称为滑脉。前文引用五脏的脉象以对应五行，此处又引用三阴三阳的脉象以对应六气。浮、滑、长属于三阳脉；沉、短、涩属于三阴脉。在寸关尺三部中观察这六种脉象，就可以知道阴阳盛衰的机理。大概阴阳脉象不会单独出现，正因为不单独出现，所以有此六种脉象相兼而见；正因为相兼，所以有一阴一阳、一阳一阴等不同情况。这是辨别阴阳虚实的方法。再结合春、夏、秋、冬四季的变化，观察六脉的变动，那么大致可以了解疾病的逆顺了。
按语：徐氏说：这一节讲的是六脉互相交错出现的景象，这里只是举例说明，也是互相错综变化，并不一定完全如此。所谓的“经”，是指手足三阴三阳经脉；“逆顺”，比如心脉宜浮，肾脉宜沉，这就叫顺；如果心脉反而沉，肾脉反而浮，这就叫逆。这也显示出脉象没有固定的形体，要根据所属经络来确定逆顺。然而脉象的浮沉或许可以相兼，但滑、涩、长、短不得同时并见，这一点也应当明白。
Chapter 4 asks: There is a method for distinguishing Yin and Yang in the pulse; what does this mean?
The response states: During exhalation, Qi emerges from the Heart and Lungs; during inhalation, Qi returns to the Kidneys and Liver. Between breaths, the Spleen receives the essence of grain, and its pulse is located in the middle.
This passage indicates that although the Yin and Yang of the pulse are manifested in the Cun (inch) and Chi (cubit) positions, the Qi of Yin and Yang is further distinguished by floating (Fu, 浮) and sinking (Chen, 沉). For instance, the Heart and Lungs reside above the diaphragm, which is Yang; thus, exhalation necessarily proceeds through them. The Kidneys and Liver reside below the diaphragm, which is Yin; thus, inhalation necessarily returns to them. The Spleen receives the essence of food and drink, serving as the source of pulse generation, located in the middle jiao. Since both exhalation and inhalation depend on it, the method of pulse diagnosis involves light palpation (floating) to assess the Heart and Lungs, heavy palpation (sinking) to assess the Kidneys and Liver, and moderate palpation to assess the Spleen and Stomach.
Commentary: The scripture's statement "exhalation" does not mean that Qi exits directly from the Heart and Lungs to the outside. Rather, because the Kidneys and Liver are below the diaphragm, their Qi rises with exhalation to reach the Heart and Lungs; hence, it is said that "exhalation comes from the Heart and Lungs." The Heart and Lungs are above the diaphragm, and their Qi descends with inhalation to reach the Kidneys and Liver; hence, it is said that "inhalation returns to the Kidneys and Liver." Exhalation involves the outward movement of Yin, while inhalation involves the inward movement of Yang. The Yin and Yang of respiration follow each other up and down, passing through the five Zang organs. This is nourished by the Spleen and Stomach receiving谷物 (grain/food) Qi. Therefore, it is stated that the pulse is in the middle. When reading this section, one must not rigidly interpret it to mean that exhaled Qi is purely Yang and inhaled Qi is purely Yin.
A floating pulse belongs to Yang, and a sinking pulse belongs to Yin; thus, they are called Yin and Yang.
When light pressure feels insufficient but heavy pressure feels excessive, it is called Floating (Fu, 浮). Floating is Yang, resembling fire which flares upward. When heavy pressure feels excessive but light pressure feels insufficient, it is called Sinking (Chen, 沉). Sinking is Yin, resembling water which moistens downward.
Both the Heart and Lung pulses float; how can they be distinguished?
The response states: A pulse that is floating, large, and scattered belongs to the Heart; a pulse that is floating, short, and choppy (Se, 涩) belongs to the Lung. Both the Kidney and Liver pulses sink; how can they be distinguished?
The response states: A pulse that is firm (Lao, 牢) and long belongs to the Liver; a pulse that feels soft upon heavy pressure but becomes solid when the finger is lifted belongs to the Kidney. The Spleen resides in the central region (Zhongzhou), so its pulse is located in the middle. This is the method of distinguishing Yin and Yang.
Supplementary explanation: A pulse that is floating, large, and forceless, feeling scattered and seemingly departing upon heavy pressure, is named Scattered (San, 散). A pulse that is floating, fine, and slow, moving with difficulty and stagnation without advancing, is named Choppy (Se, 涩). A pulse that is deep, forceful, solid, large, wiry, and strong, feeling extremely hard and immovable upon heavy pressure, is named Firm (Lao, 牢). A pulse that is large and long, slightly wiry, feeling solid under the finger upon heavy pressure, and forceful in both moderate and deep palpation, is named Solid (Shi, 实). How to distinguish the floating pulses of the Heart and Lung? Since the Heart belongs to Fire, its pulse image is floating, large, and scattered. Since the Lung belongs to Metal, its pulse image is floating, short, and choppy. How to distinguish the sinking pulses of the Kidney and Liver? Since the Liver belongs to Wood, its pulse image is firm and long. Since the Kidney belongs to Water, its pulse image feels solid upon lifting the finger and pressing, reflecting the nature of water being soft on the outside and hard on the inside. The Spleen belongs to Earth, residing in the center, flourishing in the four seasons, and nourishing the four other Zang organs. Its pulse comes leisurely and harmonious, neither sinking nor floating, hence it is said that its pulse is in the middle.
There are pulses with one Yin and one Yang, one Yin and two Yangs, one Yin and three Yangs; there are also pulses with one Yang and one Yin, one Yang and two Yins, one Yang and three Yins. Does this statement imply that all six pulse positions at the Cun Kou move simultaneously?
The response states: This statement does not refer to all six pulses moving simultaneously. It refers to the characteristics of Floating (Fu, 浮), Sinking (Chen, 沉), Long (Chang, 长), Short (Duan, 短), Slippery (Hua, 滑), and Choppy (Se, 涩). Floating is Yang, Slippery is Yang, Long is Yang; Sinking is Yin, Short is Yin, Choppy is Yin. "One Yin and one Yang" means the pulse comes Sinking and Slippery. "One Yin and two Yangs" means the pulse comes Sinking, Slippery, and Long. "One Yin and three Yangs" means the pulse comes Floating, Slippery, and Long, occasionally presenting a Sinking quality. "One Yang and one Yin" means the pulse comes Floating and Choppy. "One Yang and two Yins" means the pulse comes Long, Sinking, and Choppy. "One Yang and three Yins" means the pulse comes Sinking, Choppy, and Short, occasionally presenting a Floating quality. Based on the meridian where these pulses are found, one determines the disease's favorable or unfavorable course (Ni Shun, 逆顺).
Extending beyond the normal position is called Long (Chang, 长); failing to reach the normal position is called Short (Duan, 短). Moving smoothly and continuously upon pressure is called Slippery (Hua, 滑). The previous section cited the five Zang pulses to correspond with the Five Elements; this section cites the Three Yin and Three Yang pulses to correspond with the Six Qi. Floating, Slippery, and Long belong to the Three Yang; Sinking, Short, and Choppy belong to the Three Yin. By observing these six pulse qualities within the three positions (Cun, Guan, Chi), one can understand the mechanism of Yin and Yang excess and deficiency. Generally, Yin and Yang pulses do not appear alone. Precisely because they do not appear alone, these six pulse qualities appear combined. Precisely because they combine, there are variations such as one Yin one Yang or one Yang one Yin. This is the method for distinguishing Yin/Yang and Deficiency/Excess. Further considering the changes of Spring, Summer, Autumn, and Winter, and observing the variations of the six pulses, one can generally ascertain the favorable or unfavorable nature of the disease.
Commentary: Xu states: This section describes the phenomenon of the six pulses appearing in mutual interweaving. This is merely an example given, showing mutual complexity, not a fixed rule. The "meridians" refer to the Hand and Foot Three Yin and Three Yang meridians. "Favorable or unfavorable" (Ni Shun, 逆顺): for example, if the Heart pulse should be Floating and the Kidney pulse should be Sinking, this is Favorable (Shun); if the Heart pulse is instead Sinking and the Kidney pulse is instead Floating, this is Unfavorable (Ni). This again shows that pulses have no fixed form; favorability or unfavorability is determined according to the specific meridian. However, it should be understood that while Floating and Sinking may coexist, Slippery, Choppy, Long, and Short cannot appear simultaneously.