《此事难知》云∶冬行秋令，当寒而温，火盛水亏云云。推作瘟病之原，固为近理。乃又云∶
火土合德，湿热相助，故为温病。是温病必原于湿热，将湿热一门，并可以不立矣。须知湿热乃
夏时之正气，瘟疫乃天地之杂气，二者迥乎不同。谓瘟病而兼湿热则有之，未闻湿热而为温病者
也。又云∶惟房室劳伤辛苦之人得之，是省房室就安逸之人，必无瘟病矣，有是理乎？每见瘟疫
盛行之年，节欲安逸之辈，往往有无端而感者，又何以称焉？又云∶多欲辛苦之人，肾水内竭，
阳气外泄，生化之源既绝，身之所存独热云云。谓瘟病中有此一种则可耳，若云瘟病尽由乎此，
则万无是理也。至于暑字，《字汇》解为夏天气热。则人之受是气者，断无尚有属阴
之理。其曰阴暑者，只因人畏暑纳凉，外受寒邪所致，仍是感冒，乃抛却现下之受寒，而止泥前
此之受暑，故以阴暑名之，亦犹之曰阴热也，有是理乎？知阴热二字之不通，则知暑之不可以
阴言也，明矣。
吴又可《瘟疫论》中驳冬温之说曰∶夏凉冬暖转得春秋之和气，岂有因其和而反致疾者？
四时之序，应寒则寒，应暖则暖，所以人得天地之正气不能为病。若夏宜热而反凉，冬宜寒
而反暖，未有不致疾者。但夏过于凉，其为病也，实时而见，惟冬令天气过于和煦，往往当时不
能为害，至来岁春夏之间方大发瘟疫，此余屡经而屡验者，实非臆说也。第夏应热而反凉，人感
寒邪而闭塞腠理，不能疏泄，其为病也，固无足异。唯冬时有非节之暖，当时不即病，必至来岁
春夏间始作，此诚不可解也。人动曰∶冬伤于寒，至春夏变为温暑病。余则曰∶冬过于温，至春
夏多发瘟疫病。彼吴又可谓冬暖夏凉不足以致疾也，吾弃不以为然。盖以暖属于春，凉属于秋，暖
与凉为春秋之正气，谓之和也始宜，若见于冬夏之令，（夏凉冬暖。）此为非其时有其气，则不
得谓之和矣。不和即为反常之戾气，此夏凉冬暖之多致疾也，又乌得言温暖清凉之未必为病也哉。
《此事难知》中说：冬季施行秋季的时令，本该寒冷却温暖，这是火气过盛而肾水亏虚等等。将其推演为瘟疫病的根源，固然合乎情理。但又说：火与土共同施德，湿热相互助长，所以成为温病。这意味着温病必定起源于湿热，那么“湿热”这一门类，就可以不必设立了。必须知道湿热是夏季的正常气候，瘟疫则是天地间的杂气，两者截然不同。说瘟疫病兼夹湿热症状那是有的，没听说过湿热本身就能导致温病的。又说：只有那些因房事过度、劳累辛苦的人才会得此病，意思是节制房事、生活安逸的人，就一定不会得瘟疫了，有这样的道理吗？我常见到瘟疫盛行的年份，那些节制欲望、生活安逸的人，往往也有无缘无故感染的，这又怎么解释呢？又说：多欲且劳累辛苦的人，肾水在内枯竭，阳气在外耗散，生化之源既然断绝，身体所剩下的只有热邪等等。如果说瘟疫病中有这一种情况是可以的，如果说瘟疫病全都是由这个原因引起的，那绝对没有这样的道理。至于“暑”字，《字汇》解释为夏天的热气。那么人受到这种气的影响，绝对没有属于阴证的道理。所谓“阴暑”，只是因为人们害怕暑热而贪凉，外感寒邪所致，这仍然是感冒，却是抛弃当下感受的寒邪，只拘泥于之前感受的暑热，所以用“阴暑”来命名，这也就像说“阴热”一样，有这样的道理吗？知道“阴热”这两个字不通顺，就知道“暑”是不可以用“阴”来形容的了，这很明白了。
吴又可的《瘟疫论》中反驳关于冬温的说法说：夏天凉爽、冬天温暖，转而得到春秋两季的平和之气，难道会因为这种平和之气反而致病吗？四季的顺序，应该寒冷就寒冷，应该温暖就温暖，因此人得到天地的正气是不会致病的。如果夏天本该热却反而凉，冬天本该冷却反而暖，没有不致病的。只是夏天过于凉爽，其发病是即时显现的；唯有冬天天气过于温和，往往当时不能为害，到了第二年春夏之间才大规模爆发瘟疫，这是我多次经历并验证过的，确实不是凭空臆测。只是夏天本该热却反常地凉，人感受寒邪而导致腠理闭塞，不能疏泄，其发病，本来就不值得奇怪。唯独冬天有时出现非时节的温暖，当时不立即生病，一定要等到来年春夏之间才开始发作，这实在无法解释。人们动不动就说：冬天受寒，到了春夏变成温暑病。我却说：冬天过于温暖，到了春夏多发瘟疫病。那位吴又可认为冬暖夏凉不足以导致疾病，我摒弃他的观点而不以为然。因为暖属于春季，凉属于秋季，暖与凉作为春秋两季的正气，称之为“和”才是适宜的，如果出现在冬夏的时令中（即夏凉冬暖），这就是非其时而有其气，就不能称为“和”了。不和就是反常的戾气，这就是夏凉冬暖多致疾病的原因，又怎么能说温暖清凉未必致病呢。
*This Matter is Hard to Know* states: "Winter follows the command of Autumn; it should be cold but is warm, indicating excessive Fire and deficient Water," and so on. Deducing this as the origin of pestilential diseases is indeed reasonable. However, it further states: "Fire and Earth combine their virtues, with damp-heat assisting each other, thus becoming warm disease." This implies that warm diseases must originate from damp-heat, in which case the category of "damp-heat" could be abolished. One must understand that damp-heat is the righteous qi (normal climate) of summer, whereas pestilence is the miscellaneous qi of heaven and earth; the two are vastly different. It may be said that pestilential diseases can involve damp-heat, but I have never heard of damp-heat itself causing warm disease. It also states: "Only those who suffer from sexual excess and hard labor contract this." Does this mean that those who abstain from sex and live in comfort will certainly not get pestilence? Is there such logic? I often see that in years when pestilence prevails, people who practice moderation and live comfortably often contract it without apparent cause. How does one account for this? It further states: "Those with excessive desires and hard labor have their Kidney water exhausted internally and their Yang qi leaking externally. Since the source of generation and transformation is cut off, what remains in the body is only heat," and so on. It is acceptable to say that this is one type among pestilential diseases, but to claim that all pestilential diseases stem from this is absolutely illogical. Regarding the character "Shu" (summer heat), *Zihui* defines it as the hot air of summer. Therefore, anyone affected by this qi cannot logically be classified under a Yin syndrome. The term "Yin Shu" (Yin Summer Heat) arises only because people fear the summer heat and seek coolness, thereby contracting external Cold pathogenic factors. This is essentially a common cold. By ignoring the current contraction of Cold and sticking rigidly to the prior exposure to Summer Heat, they name it "Yin Shu." This is akin to saying "Yin Heat." Is there any logic in this? If one recognizes that the phrase "Yin Heat" is nonsensical, it becomes clear that "Shu" cannot be described as "Yin."
Wu Youke, in his *Treatise on Pestilence*, refutes the theory of Winter Warmth, stating: "Summer coolness and winter warmth result in obtaining the harmonious qi of Spring and Autumn. Could it be that this harmony causes illness? The order of the four seasons dictates that it should be cold when it ought to be cold, and warm when it ought to be warm. Thus, humans receiving the righteous qi of heaven and earth do not become ill. If summer should be hot but is instead cool, or winter should be cold but is instead warm, illness inevitably results. However, if summer is excessively cool, the resulting illness appears immediately. But if winter weather is excessively mild, it often causes no harm at the time, only to erupt into widespread pestilence during the following spring and summer. This is something I have experienced and verified repeatedly; it is truly not a baseless speculation. Indeed, if summer should be hot but is cool, humans contract Cold pathogenic factors, causing the couli (pores) to close and preventing dispersion; the resulting illness is hardly surprising. However, the fact that non-seasonal warmth in winter does not cause immediate illness, but only manifests in the following spring and summer, is truly inexplicable. People often say: 'Injury by Cold in winter transforms into Warm or Shu diseases in spring and summer.' I say: 'Excessive warmth in winter leads to frequent pestilential diseases in spring and summer.' Wu Youke claims that winter warmth and summer coolness are insufficient to cause disease, an opinion I reject. Warmth belongs to Spring, and coolness belongs to Autumn. Warmth and coolness constitute the righteous qi of Spring and Autumn, and are appropriately termed 'Harmony' (He). If these appear during the commands of Winter and Summer (i.e., summer coolness and winter warmth), this constitutes 'qi present out of season,' and thus cannot be called 'Harmony.' Disharmony is abnormal, pernicious qi. This is why summer coolness and winter warmth frequently cause disease. How can one argue that warmth and coolness do not necessarily cause illness?"