褚澄氏曰∶男女交合，阴血先至，阳精后冲而成男，反则成女，此一说也。
东垣云∶经水才断一二日，血海始静，交合成男。四五日后，血脉已旺，交合成女，此又一说也。顾或有
经始断，而交合生女，经久断而交合生男者。亦有三五日交合无孕，八九日交合有孕者，独何与。
《广嗣要略》云∶实阳能入虚阴，实阴不能受虚阳也。又谓∶阳微不能射阴，弱阴不能摄阳，信斯言也。
世有 羸之夫，怯弱之妇，屡屡受胎，虽欲止而不能止者，亦有壮年精力过人，乃艰于嗣育者，独何欤。
丹溪曰∶妇人以经水为主，然富贵之家侍外家既多，其中岂无月水当期者乎，有已经前夫频频生育，取之以
图其易者，顾亦不能得胎，更遣与他人，转 亦生男矣。岂不能受孕于此，而能受孕于彼乎。
本立曰∶父母之生子，如天地之生物。易曰∶坤道其顺乎，承天而时行，夫知地之生物不过顺承乎。天则
知母之生子，亦不过顺承乎，父而已知母之顺承乎。父则种子者，当以男子为主。男子为主而交媾之时，又以
百脉齐到为善，交媾能而百脉齐到，虽老弱易泄，亦可以成胎。若百脉参差，虽少壮康宁难泄，亦不能
成胎。若男女之辨，不以精血先后为拘，不以经尽几日为拘，不以夜半前后交媾为拘，只以男女精血，各
由百脉齐到者，别胜负耳，是故精之百脉齐到，有以胜乎血，则成男矣。血之百脉齐到，
有以胜乎精，则成女矣。至有产而不育者，有育而不能寿者，有
寿而黄 无疆者，则亦以精之坚脆分为修短耳。
Chu Cheng stated: When man and woman engage in intercourse, if the Yin blood arrives first and the Yang essence follows to strike, a male child is conceived; if reversed, a female child is conceived. This is one theory.
Li Dongyuan said: One or two days after menstruation ceases, the Blood Sea (Chong Mai, the sea of blood) has just calmed down; intercourse at this time results in a male. Four or five days later, when the blood vessels are vigorous, intercourse results in a female. This is another theory. However, there are cases where intercourse immediately after menstruation yields a female, while intercourse long after menstruation yields a male. There are also instances where conception does not occur within three to five days of intercourse, but occurs eight or nine days later. Why is this so?
The *Guang Si Yao Lue* states: Solid Yang can enter Empty Yin, but Solid Yin cannot receive Empty Yang. It further says: Weak Yang cannot shoot into Yin, and weak Yin cannot grasp Yang. If one believes these words... In the world, there are emaciated men and timid, weak women who conceive repeatedly, unable to stop even if they wish to do so. Conversely, there are men in their prime with abundant vitality who struggle to have offspring. Why is this?
Zhu Danxi said: Women are primarily governed by menstruation. Yet, in wealthy households with many concubines, are there not some whose menstrual cycles are regular? Some women, having been frequently pregnant by a former husband, are taken for ease of conception, yet fail to conceive. If transferred to another man, she may conceive a male. Can it be that she cannot conceive with one man but can with another?
Ben Li said: The parents' generation of children is like Heaven and Earth generating all things. The *I Ching* states: "The way of Kun (Earth) is its submission, receiving from Heaven and acting according to the seasons." Knowing that Earth generates things merely by submitting and receiving, we know that a mother's bearing of children is also merely submitting and receiving from the father. The father is the sower of seeds, and thus should take the lead. With the father taking the lead, during intercourse, it is auspicious for the Qi of all meridians to arrive simultaneously. If the Qi of all meridians arrives simultaneously during intercourse, even an old or weak man prone to premature emission can achieve conception. If the Qi of all meridians is disordered, even a young, strong, and healthy man who finds it difficult to emit can fail to achieve conception. Regarding the determination of sex, one should not be bound by the sequence of essence and blood arrival, nor by the number of days since menstruation ceased, nor by whether intercourse occurs before or after midnight. Instead, one should distinguish victory based on which party's essence and blood, arriving via the simultaneous convergence of all meridians, prevails. Therefore, if the simultaneous convergence of essence's meridians prevails over blood's, a male is conceived. If the simultaneous convergence of blood's meridians prevails over essence's, a female is conceived. As for those born but not raised, those raised but not living long, or those living long without limit, these differences in lifespan are determined by the firmness or fragility of the essence.