What is Inner Fire in the book Taoist Yoga: Alchemy and Immortality?

I started to understand the book better, but I have a question for someone who read it: what is the "inner fire" that continously appears in it? At the glossary it appears to be talking about some processes for the transmutation, but from what i saw until now, it is a force/energy in the body. Any ideas?

When I first asked about this book on this website - over 10 years ago - I was told not to read it because it was too dangerous. So then it took me many years later to realize it was the ONLY book I could read that specifically answered questions I had from training.

So regarding your question on "inner fire" - you can just word search the book in this format:
https://archive.org/stream/TaoistYogaAlchemyAndImmortalityLuKuanYCharlesLuk/Taoist Yoga Alchemy and Immortality Lu K’uan Yü (Charles Luk)_djvu.txt

There are many terms in the book that are interchangeable - and so it is confusing.
So searching inner fire - we discover - it is actually the prenatal qi or yuan qi - called prenatal vitality also.

By regulated breathing is meant deep breathing that reaches the lower abdomen to arouse the inner fire and then bring pressure on the generative force already held there forcing both fire and generative force to rise in the channel of control in the spine to the head.

So we see here - inner fire is not the generative force or yin qi.

detailed explanation of inhalation and exhalation of outer air to kindle the inner fire to cleanse and purify the generative force during the microcosmic orbiting.

And the light that is produced by the inner fire - is NOT the same as the light when the third eye opens up:

Therefore, when the outer alchemical agent has been gathered, it is necessary to roll the eyes to unite the positive with the negative principles in order to develop spirit in the bright light that emerges from the original cavity of spirit between and behind the eyes. This bright light shows the exact position of that cavity and should not be confounded with the luminous inner fire that rises to the head during the microcosmic orbiting as we have said earlier.

So another way to explain this is that light seen internally is from the "yang qi" - and so is the "relative void" but when you build up the yang qi - then the yuan qi manifests the Yuan Shen - and this is the "absolute void" and this light can be seen externally as well - and is much brighter.

In Taoist yoga the negative vitality is represented by the dragon and the positive vitality by the tiger, while their ‘copulation’ brings into manifestation the original spirit in its bright light. When original or prenatal spirit manifests thus, it should be driven into the lower tan t’ien centre

So the original or prenatal spirit is also called Yuan Shen.
positive vitality is yang qi.

The arousal of the genital organ feeds the inner fire in the stove which transforms the generative fluid derived from digestion of food into negative generative force to fortify the body and enliven spirit thereby lengthening the span of life.

So negative generative force is yin qi.
So the "inner fire" transforms food into  yin qi but the "inner fire" is STRONGER than then yin qi.

With inner fire soaring up in his body, his (essential) nature is replaced by his heart so that desires and passions fill his being.

So here we have at age 16 - the "separation" of Shen or spirit that soars up - and then the qi that is lost as fluid going down. Heaven and Earth are no longer harmonized but separated - into heart and reproductive organ as kidney. So the inner fire appears to be the "yang qi" or "po soul" that grabs onto the hun soul (yin qi) that goes out the eyes.

in order to drive spirit into the cavity of vitality (under the navel). This is like a blacksmith using his bellows; the air from it blows the inner fire which, becoming intense, transmutes the generative force into vitality.

Here we have another hint:

By ‘shifting’ is meant arousing the inner fire so that both outer and inner fires act on each other in order to enlarge all obstructed psychic channels and clear them of obstructions. Since positive fire is stronger than generative force, it drives the latter into all parts of the body to remove all impurities thus preventing the development of ailments.

So positive means yang. Inner fire means yang fire or yang qi which also means "with substance."

these two kinds of breathing are motivated by the sole thought of ‘leading the inner fire’ to turn the wheel of the law (for the double purpose of stopping all wandering thoughts and of blocking the drain of generative fluid).

As I said, "substance."
So that goes to the head instead of out the lower body.

When the lower abdomen is full of generative 
force the inner fire is stopped by discontinuing all (alchemi¬ 
cal) breathing through the nose.

So more hints that the inner fire is indeed qi or vitality:

The method of gathering the microcosmic inner alchemical agent consists of rolling the eyes from left to right and vice versa to raise and lower the inner fire. The meditator should first direct his eyes down and roll them from the left up to the top of the head, thence lowering them to the right to look into the navel and the centre of vitality below it to complete a full turn as indicated in the diagram

So here we have - hints of how the inner fire is the yang qi that then turns into the yuan qi - to manifest the Yuan Shen, opening up the third eye:

This chapter discusses the method of using the micro¬ cosmic inner fire that passes through sublimating phases at the cardinal points D and J (see figure 2 on page 13) to produce the (microcosmic inner alchemical agent, which method is also called ‘inner copulation’ (nei chiao kou) meaning that after you have gathered enough of the (micro¬ cosmic) outer alchemical agent, true vitality, driven by ventilation and fire, will soar up to the brain; you should then roll your eyes from left to right in a complete circle in order to push vitality up and down so that the vital breath in the brain unites with the nervous system.

So true vitality also means Yuan Qi or prenatal vitality.

This negative state comes from an interruption of the inner (vital) breath which stops giving support to spirit fixed in the cavity of vitality (below the navel) thereby cooling the inner fire in the lower tan t’ien and preventing the light of the elixir from manifesting.

So to build up the spirit or shen - the qi has to be built up - the yuan qi - which is built up from the inner fire.

‘To remedy this negative state requires concentration of true inner fire which is done by fixing spirit in the lower tan t’ien, the source of foetal breath, by drawing the pupils of the eyes close to each other in order to bring the cavity of vitality into focus and by using the bellows to bring quick fire into action; as a result of pointed concentration a mass of true inner fire will soar up causing spiritual light in the cauldron to illuminate the whole body the four elements of which

So here for the first time we have "true inner fire" instead of just normal "inner fire."
So the yang qi as inner fire is transformed into "true vitality" or "true inner fire" aka Yuan Qi.
This process is from the Shen being fixed, concentrated, or visualized as fire below the water (the generative fluid) - thereby creating Air - the Qi as inner fire. This is the essence of the practice.

Seven kinds of fire, derived from spirit, to transform the generative force into vitality:

In this event inner fire should be gathered and lifted to produce spiritual fire which will emit the golden light

So now we have "spiritual fire" that is created from "inner fire." So it is the "true inner fire" that opens the third eye as the "spiritual fire" or prenatal spirit.

Therefore, when thoughts arise the practiser should use the inner fire that has flared up to turn the wheel of the law (i.e. direct it into the microcosmic orbit) to wipe them out, but he should never turn it when unsteady concentration has cooled down the inner fire so as not to injure the immortal seed.

So this is a subtle difference - just as when a person turns 16 - the inner fire rises up to the head based on thoughts of passion, causing the separation and loss of the generative force - and so this has to be reversed through meditation.

Ascent and descent of inner fire in the microcosmic orbit: When breathing in, the heart, spirit and thought should rise together in the channel of control from the cardinal point A at the base of the penis to the cardinal point G on the top of the head, and when breath¬ ing out, the heart, spirit and thought should together go down in the channel of function from the cardinal point G to A (see figure 2 ). The ascent is positive and the descent is negative.

So this is the glossary definition - we can see then that "inner fire" is the alchemical meditation process of the shen and the thought as qi - together - that drives, cleanses and purifies the generative force.

A full fourfold breathing consists of in and out breaths with corresponding ascent and descent of inner fire in the microcosmic orbit which contributes to the immortal breath.

So with the outer alchemical agent - as the breath goes in and down, the inner fire goes up and vice versa and builds up the immortal breath or yuan qi.

the passing of inner fire through sublimating phrases at the cardinal points D and J of the microcosmic orbit, for the purpose of transmuting vitality into spirit whose full development causes a bright light, called the mysterious gate (hsuan kuan) to manifest in the original cavity of spirit between and behind the eyes.

So the generative force or jing (yin qi) is transformed into inner fire as yang qi aka

the psychic fire

which is transformed into "true vitality" as yuan qi that manifests the prenatal or yuan shen light.

Driving the fire (into) is driving into the microcosmic orbit the inner fire which then passes through the sublimating phases at D and J to' gather the inner alchemical agent so that true vitality soars up to the brain which will then develop fully, causing a bright light, called the mysterious gate, to manifest between the eyes.

Stove (lu ): A cavity where the inner fire is kindled by regulated breathing to put the generative force into microcosmic orbit and transmute it into vitality.

So part of this process is the regulated or synchronized breathing with the heart beat - cardiorespiratory synchronization.

Cardiorespiratory synchronization during Zen meditation. - NCBI

https://www.ncbi.nlm.nih.gov/pubmed/15940533

by D Cysarz - ‎2005 - ‎Cited by 141 - ‎Related articles

Eur J Appl Physiol. 2005 Sep;95(1):88-95. Epub 2005 Jun 7. Cardiorespiratory synchronization during Zen meditation. Cysarz D(1), Büssing A.

So the inner alchemical agent is the Yuan Qi or prenatal true vitality.
The outer alchemical agent creates the inner fire - through breathing - and rotating the eyes (so the shen or spirit synchronizes with the qi).
Yuan Qi is also called "prenatal generative force" - such that yin qi is just "premature" yuan qi.

What do you mean by ‘driving the fire’? Answer It is the positive fire as will be explained in Chapter 6. Chapter 4 has already dealt with gathering the microcosmic outer alchemical agent in order to return it to the stove (in the lower abdomen); since this agent is still not yet sublimated by fire, it can drain away like tea poured continuously into a cup which overflows and spreads outside. This positive fire can transmute the agent in the stove into vitality (in order to stop its overflow).

And so it is the third eye that actually builds up the yuan qi:

the psychic strength to develop, expand and unite into one whole reaching the core of the brain where it transmutes the (microcosmic) outer alchemical agent (already gathered there) into life-preserving true vitality;

The microcosmic sublimation of vitality....to raise positive fire

So here again we have vitality or qi as fire.

heart (the house of fire) by driving his mind into the field of concentration so as to still and disengage it from sense data.

So the heart is the shen but it is powered by the liver as the yin qi - and so with the eyes open this goes out of the eyes. So the inner fire is the alchemical process of reversing this loss - and uniting the shen  and the yin qi of the shen back with the yang qi (the inner fire) - of the kidneys. So then the yin qi then restores the yang qi and through purification and cleansing - creates the yuan qi.

the element of fire in spirit goes down to scorch the element of water in the lower abdomen which will be transformed into steam that will soar up linking the heart and lower abdomen. When he wakes up and opens his eyes, spirit returns to his organ of sight thereby disengaging the heart from the lower abdomen which will not reunite even if he starves for a week.

So this is the yin qi in the shen - and the steam is the increased qi created from meditation - with the eyes open this does not happen.

If the outer sun and moon do not mingle their lights the inner water and fire do not ‘copulate’ and prenatal true vitality cannot manifest.

So the outer sun and moon means the left eye and right eye - need to be rotated with the eyes closed - the inner water and fire is the heart and kidneys.

If they are left to themselves to follow their postnatal course the element of fire will remain dry and that of water will continue wet, with the former soaring up and the latter going down, both running in opposite directions. If water is not scorched by fire it will not evaporate to become steam that soars up.

So the "outer agent" gathered wrongly - is the evil fire of passion - with the sun and moon being disconnected - the left and right eye.
It will...

the most you can expect is to improve your health by eradicating all ailments.

So that is the DIFFERENCE between the inner fire as "yang qi" and the TRUE inner fire as yuan qi from cleansing and purification.
The inner fire as yang qi has the power to clear out yin qi blockages to heal the body - but it is not the real spiritual energy of the yuan qi.

The outer agent which you have gathered is an illusory false one created by wrong thoughts; hence the nocturnal emission. This illusory agent is the generative fluid which contains the evil fire that develops when it is aroused by the vital force.

So the qi activates the evil fire - but it is still just yang qi as inner fire and not the true inner fire.

The latter is like a ball of fire, the size of a bullet, in the lower tan t’ien centre which will become hot causing the root of the genital organ to vibrate and set prenatal vitality in motion.

True inner fire.

The light of the eyes directed downward is positive

So that is to build up the yang qi -  or positive qi.

Lowering the fire (to cause the negative fire to retreat so that the positive yang develops fully

to the heart as the vital breath of the element of fire

If the element of fire is strong in the heart it will scorch the blood; so the practiser should avoid excessive talking and thinking to rest his heart. This restfulness will invigorate spirit and body, for spirit withers in disturbance and thrives in stillness

This is the proper time to stop fire (produced by regulated breathing)

So at the end of the practice - external breathing is no longer used - only the qi is moved with the spirit ... but there is STILL internal heat.

Hence the divine mirror which is achieved only after positive fire has transmuted the demons into prenatal (divine) spirit.

So here - the fire is not the same as the spirit...

look inward to produce divine fire there. With the fire of positive spirit in the head, the practiser should concentrate on it in silence so that the fire above will descend and the fire below will soar up

And so the Qi or vitality has to surround the spirit..

This continual sublimation will result in deeper concealment of the spiritual fire in the light of vitality so that the positive spirit will be kept in its original cavity (tsu ch’iao).