In ancient China, the term fan (反; fǎn; 'return', 'reversion', 'inversion') became associated with a basic concept within Daoism: the Daodejing remarks "Reversal is the movement of the Way ...

"[6] Fan (反) and huan (還) both have the significance of 'reaction' or 'return', as "when some kind of reverse change takes place as the result of a former action, or when a cyclical process brings back the phenomena to a state similar to that at the beginning, or identical with it.

"[7] In the classic Daodejing the terms 反; fǎn, 歸; guī, and 复; fù each share the semantic field of 'reversal', 'return', 'reversion', 'renewal'.

The philologist Victor H. Mair says that all three "suggest the continual reversion of the myriad creatures to the cosmic principle whence they arose", which corresponds with the philosopher Mircea Eliade's "myth of the eternal return".

Now, When neither harms the other, integrity accrues to both [故德交歸焉]"The Chinese philosopher and historian Fung Yu-lan said that fan meaning 'reversion' and fu meaning 'return' refer to the greatest of all the laws underlying phenomenal change: "if any one thing moves to an extreme in one direction, a change must bring about an opposite result".

[皆生於土而反於土]""If they [ancient "hidden scholars"] had received the mandate of the times and been able to carry it out widely for all under heaven, they would have returned to the unity that leaves no traces [則反一無跡].

Not having received the mandate of the times and greatly stymied by all under heaven, they sunk their roots deep in utter tranquillity and waited.

""The principles by which they follow in sequence upon one another, The mutual causation through which they conspicuously revolve, Their reversal after reaching an extreme, Their beginning after coming to an end [窮則反，終則始], These are the qualities inherent in things.

On a cosmic level, fan characterizes the Dao itself, as all phenomena tend over time (through death, decay, or destruction) to revert to the undifferentiated root from which they emerged.

[11] The Huainanzi uses several near-synonyms with fan referring to the Daoist doctrine of "returning to one's original, undifferentiated nature", a pervasive theme that occurs more than ninety times in fifteen of the twenty-one chapters.

[12] Non-differentiation refers to the "perfect beginning before distinction, division, multiplicity and separateness emerged: everything was smoothly and harmoniously blended into one compact whole; everything was simultaneously 'together'.

"[13] The Huainanzi describes the ability of a zhenren ('genuine/true person') to "return to the origin — the state of primordial undifferentiation, the perfect beginning before things appeared as distinct and separate".

[16] An early example of this first meaning is the c. 300 BCE Guodian Chu Slips manuscript entitled Taiyi Shengshui (太一生水, The Great One Generated Water), which states that Water, after being generated, returns (fan) to the Great One (Taiyi) [水反輔大一] to assist it in forming Heaven.

[19] Lau reasoned that if change is cyclic and a thing that reaches the limit in one direction will revert to the opposite direction, then the central Daoist precept that "To hold fast to the submissive is called strength"[20] becomes both "useless" because if both development and decline are inevitable, the purpose of the former is to avoid latter, and "impracticable" because it advocates that we should remain stationary in a world of incessant change.

When something has grown to its ji (極, "utmost point"), it decreases or reverses to its contrary, as do Yin and Yang or night and day.

[17] Norman J. Girardot says the Dao is a living thing that follows a "law of cyclic return", which manifests creative activity and life-giving force.

"[30] Van Norden says any conscious effort to anticipate changes in the world is doomed to failure, because no one knows the "limits" or points at which reversal will occur.

He agrees with D. C. Lau that cyclical change is not inevitable, the Daodejing says disaster "crouches" beneath good fortune, but it does not "necessarily follow" it.

"[31] A professor of Chinese philosophy and religion says notion of fan suggests not only the need to "return" to the Dao, but also that the Daoist way of life would inevitably "appear the very opposite of 'normal' existence, and that it involves a complete revaluation of values".

[35] Huanyuan in Daoist neidan is equated with the goal of returning to one's benxin (本心, "original mind") in Chan Buddhism.

Daoist cosmogony typically involves the progression from Nonbeing to Oneness, followed by the emergence of the yin and yang principles, which join in generating and differentiating the myriad beings.

Through cyclical refining and smelting, the alchemical ingredients revert to their original condition, and yield their jing (精, "pure essences").

[37] Internal neidan alchemy uses cosmological language both to explain the fundamental cosmic configurations and to guide adepts to a primordial order, with the belief that inverting the cosmogonic process will fan ("return") to the pre-cosmological state of existence.

55) says, "If eternal integrity never deserts you, You will return to the state of infancy", which suggests that "human vitality is fully charged upon parturition and constantly discharges with every natural cycle of breath".

[40] Returning to the origin, the womb, or the embryo implies the idea of "rebirth and renewal as a kind of countercurrent to ordinary life".

[41] One of the most central ideas in physiological alchemy is "retracing one's steps along the road of bodily decay"; in addition to the above fan (反) and huan (還) meaning "regeneration; reversion", other technical terms include xiu (修, "restoration"), xiubu (修補, "repair"), and fu (復, "replenishment").

A related neidan theory is making certain bodily fluids, particularly products of the salivary and testicular glands, flow in a direction opposite to the usual, which is expressed by such terms as niliu (逆流) or nixing (逆行).

[42] Authors of Daoist alchemical texts repeatedly give cosmogony as the chief example for the process of shun (順, "continuation"), a series of stages that lead to degeneration and ultimately to death, whereas neidan is based on the opposite notion of ni (逆, "inversion").

In neidan terminology, huixin (回心, "turn one's heart toward") means "to convert", while huijing (回精, "reverse the sperm/essence") connotes flowing against the current and refers to a Daoist sexual practice that supposedly "makes the essence go up" into the brain.

[44] Besides Daoist inner alchemical texts, the notion of turning inward (fan 反 or 返) is also prevalent in Buddhist and Confucian traditions.