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Cheng Mingqian stated: If one believes in Chu's theory, then why does seminal emission occurring first result in a male child, while emission occurring later results in a female child? If one believes in Li Dongyuan's theory, then why does intercourse immediately after the cessation of menstruation yield a female, whereas intercourse after a longer interval yields a male? Furthermore, there are cases where intercourse four or five days before menstruation fails to conceive, yet intercourse eight or nine days later succeeds. Why is this? Yu Zimu further asserted: "Weak Yang cannot penetrate Yin, and weak Yin cannot grasp Yang." If these words are believed, then why do frail and debilitated husbands and timid and weak wives frequently conceive, while men with robust blood and Qi (vital energy) and abundant vitality often remain sterile and fail to produce heirs? Danxi's discussion on treatment focuses primarily on the woman's menstrual flow. However, in wealthy households, concubines are common; surely not all of them have regular menstruation? Moreover, a woman who has frequently given birth previously might fail to conceive when married to a new husband seeking fertility. How can she conceive with him but not with the previous partner? Generally speaking, parents giving birth to children is akin to Heaven and Earth generating all things. The *I Ching* (Book of Changes) states: "The Way of Kun (Earth) is its submission, receiving from Tian (Heaven) and acting according to time." Knowing that Earth generates all things by submitting to Heaven, we know that a mother bearing children also submits to the father. Understanding that the mother submits to the father, we must ask: Is conception primarily dependent on the woman or the man? If it depends on the man, regardless of age, strength, health, or illness, and whether his essence is easy or difficult to emit, the key is that at the moment of sexual union, the Qi of the hundred vessels arrives simultaneously. To distinguish between male and female, one should not be constrained by the sequence of essence and blood arrival, the number of days since menstruation ended, the time of night (before or after midnight), or the strength of the parents. One should only distinguish based on which—essence or blood—arrives via the hundred vessels more dominantly. Thus, if the simultaneous arrival of essence via the hundred vessels surpasses that of blood, a male is conceived; if the simultaneous arrival of blood surpasses that of essence, a female is conceived.

Li Dongbi stated: The *I Ching* says, "One Yin and one Yang constitute the Dao (Way)." When male and female unite their essence, all things are transformed. The Way of Qian (Heaven) forms the male, and the Way of Kun (Earth) forms the female. This describes the generative mechanism of male and female, and the virtuous capacity of Yin-Yang creation. Chu Cheng of the Southern Qi dynasty said: If blood arrives first and envelops the essence, a male is born; if essence arrives first and envelops the blood, a female is born. If Yin and Yang arrive equally, a non-male, non-female body is formed. If essence and blood scatter and divide, it indicates twins or multiple fetuses. The *Daozang* (Daoist Canon) states: Conception on the 1st, 3rd, or 5th day after menstruation ends results in a male; on the 2nd, 4th, or 6th day, a female. Li Dongyuan stated: Conception within 1-2 days after the Blood Sea (uterus) is clean results in a male; on days 3-5, a female. The *Shengji Jing* (Holy Relief Classic) states: If Qi moves to the left, Yang nourishes it to form a male; if Qi moves to the right, Yin nourishes it to form a female. Zhu Danxi rejected Chu's view and supported Li Dongyuan's, basing his argument on the *Shengji Jing*'s theory of left and right, attributing it to the ligaments of the left and right uterus. His explanation was considered thorough. I privately believe Chu's view cannot be entirely dismissed, nor is Li Dongyuan's entirely correct. Chu spoke of the sequence of essence and blood; the *Daozang* spoke of odd and even days; Li Dongyuan spoke of the waxing and waning of women's blood; the *Shengji Jing* and Danxi spoke of the left and right of the uterus. Each held a partial truth; integrating them reveals the complete principle. Can single-gender fetuses be determined by days, but can twins/multiples also be determined by days? Historical records show single births of three or four children, sometimes mixed gender, some male-heavy, some female-heavy. Does the "1,3,5 for male, 2,4,6 for female" rule hold true? Is there any logic that a male is conceived on one day and a female on the next? Therefore, the theories of Chu, the *Shengji Jing*, and Danxi regarding essence/blood and uterine left/right are insightful, while those of the *Daozang* and Li Dongyuan regarding days are questionable. Wang Shuhe's *Mai Jing* (Pulse Classic) distinguishes genders of irregular births by the floating/sinking of pulses on the left/right; Gao Yang's *Mai Jue* (Pulse Manual) distinguishes twin shapes by pulse direction and smoothness/obstruction. These are likely speculative and not definitive conclusions.

Shenzhai commented: The above seven passages present differing theories on determining fetal sex during conception. The Classics state: "Left and Right are the pathways of Yin and Yang." "Male and Female are the images of Yin and Yang." Thus, when Yin and Yang harmonize, all things are born; when husband and wife unite, male and female forms arise. It is evident that the birth of males and females is rooted in the principles of Yin and Yang. Therefore, Chu Cheng distinguished sexes by the sequence of essence and blood, Li Dongyuan by odd/even days, and Cheng Mingqian by the simultaneous arrival of the hundred vessels. All these views are imperfect. Hence, Danxi criticized Chu and Li as incomplete, relying instead on the *I Ching*'s concept of Qianyuan initiating life and Kunyuan nurturing life. Lou Quanshan praised this as reaching the pinnacle of subtlety and revealing what predecessors had not. The idea that the uterus divides into left and right to determine sex is flawed. The uterus is the Gate of Life (Mingmen); in women, the Bao Luo (womb) resembles a closed bowl. It does not split into two; claiming left/right division implies two uteri, which is baseless speculation. The *Shengji Jing* discussed Yin/Yang Qi moving left/right to determine sex, not anatomical left/right uteri. Moreover, during intercourse, both parties contribute essence; where is the blood? Chu, Li, and Danxi conflated essence and blood. Have you ever seen male-female union involving only female blood? Previous experts' theories contain many errors; I venture to clarify them.