在唐代，中国道教发展至巅峰，外丹学说盛行，但其副作用已显现。太宗之后，服用外丹而死的案例频发。面对此种局面，司马承祯、吴筠等人强烈推崇内丹学说，以批判外丹之弊，并开创了道教炼养长生内丹派的先河。
吴筠（字贞节），华州华阴人，因擅长经史及文辞未能入仕。自幼修道，在嵩山学习潘师正传授的上清经法，最终掌握了奥义和法术。在玄宗开元年间，他离开嵩山南游金陵、访道于茅山后隐居其中。
玄宗闻名他的大名，遣使征召他后，吴筠成为待诏翰林。他在朝会中与文武官员并列就座，对朝臣启奏有所评论，有时言辞激切以表忠心。天宝年间，他预测国家将来大乱，上奏请求返归嵩山，但多次未被批准，因此玄宗下诏另建道院让他住持传道。
安禄山、史思明叛乱前夕，他再次向玄宗上奏请求回茅山，这次获得同意。不久中原大乱时，他东游会稽，与李白等诗人往来，其生活较为平静。在这段混乱时期，有许多文人参与他们的活动。
唐代宗大历十三年（公元778年），吴筠在越中去世，被谥号“宗玄先生”。他的主要著作包括《玄纲论》、《神仙可学论》以及其他几卷今已失传，而《宗元先生文集》仍流传至今。
二/Internal Alchemy and the Creation of Future Lineages
Wu Yin's internal alchemy thought is characterized by his emphasis on "guarding quietude and eliminating agitation." He believed that humans rely on jing, qi, and shen, with the primary rule being to guard quietude. Wu Yin cited from the "Tortoise Shell Scripture" to explain that a person's fate lies within themselves, not in heaven. Humans share one vital energy with heaven and earth, which endures forever; however, people often die prematurely due to exhausting their vital energy.
The root cause of exhaustion is excessive movement or "agitation," which originates from desires. Desires manifest as attitudes towards sensory pleasures such as colors, sounds, scents, tastes. If one indulges in these things too quickly without self-control, they will confuse their intentions and disrupt their minds.
This leads to ruin for both body and spirit until death ensues. Therefore only remaining tranquil can lead to becoming immortal. To illustrate this point of guarding quietude while eliminating agitation through practice of "carefree indifference" (unaffected by joy or sorrow), he emphasized maintaining a state of calmness so that vitality can flow freely – thus paving an essential path towards immortality.
Furthermore Wu Yin believed that it was possible for mortals to become immortals if they pursued this goal diligently enough: either naturally inheriting celestial energies resulting in enlightenment without effort or cultivating spiritual practices leading to enlightenment after sustained efforts over time.
In summary he argued against generalizations about attaining immortality based solely on individual experiences rather than understanding the various ways it could be achieved depending on individual circumstances.
Wu Yin lived a life dedicated to mastering internal alchemy practices – teaching others how maintain balance between yin-yang forces inside oneself thereby achieving long life & health through meditation techniques focusing primarily upon controlling breath patterns using visualizations & postures etc., promoting harmony between body-mind-spirit components at all times striving toward perfect equilibrium with nature itself - believing its ultimate aim lay beyond mortal bounds seeking transcendence into realms where aging has no meaning because true freedom exists there free from any constraints limiting potentiality inherent within us all regardless age!
