或謂腎氣丸為補水之劑，以熟地大補精血故也。不知精血足則真陽自生，況山藥茱萸，皆能濇精固氣，氣者火也。水中之火，乃為真陽，此劑水火兼補，不寒不燥，至平淡，至神奇也。或曰腎氣丸實補肝藥也。腎為肝母，子虛則補母之義，古云：肝腎之病，同一治也。
Some people say Shènqì Wán is the prescription to tonify water, this is because shúdì is used in order to greatly tonify the jīng/essence and blood. But they are ignorant that if jīng and blood are sufficient then true yáng will naturally be generated, moreover shānyào and [shan] zhūyú, both have the function of astringing the jīng and securing the qì, the qì, this is fire. Fire within water, this is called true yáng, and this prescription tonifies both water and fire, it is neither cold nor drying, though it appears ordinary, its [effects] are miraculous. Some people say Shènqì Wán is actually a formula for tonify the liver. The kidney is the mother of the liver, this is the significance of if the child is deficient then tonify the mother. The ancients said: for disease of liver and kidney, use one treatment to treat [both]. (My note, this is a continuation of the theory that kidney and liver have the same source).
昂按：腎氣丸熟地溫而丹皮涼，山藥濇而茯苓滲，山茱收而澤瀉瀉，補腎而兼補脾，有補而必有瀉，相和相濟，以成平補之功，乃平淡之神奇，所以為古今不易之良方也。即有加減，不過一二味，極三四味而止，今人多揀本草補藥，任意加入，有補無瀉，且客倍於主，責成不專，而六味之功反退處於虛位，失製方之本旨矣。此後世庸師之誤也。
[Wang] Áng explains: Shúdì in Shènqì Wán warms and dānpí cools, shānyào astringes and fúlíng percolates, shānzhū constrains and zéxiè drains. [The formula] tonifies the kidney and additionally tonifies the spleen, for tonification there must be draining, mutually harmonising and mutually beneficial, to construct a formula] that is balanced and tonifiying, this is the miraculous [effect] of common [formula], therefore, this is an effective formula that has remained unchanged throughout history. In regards to modifying, do not exceed one or two herbs, at most three or four herbs and then stop. People now days select excessive amount of tonifiying herbs from the Běncǎo, arbitrability modify [the formula], add tonifying but ignore draining [herbs], causing guests [auxiliary herbs] to overshadow the primary [herbs], the intended task [of the formula] becomes unfocused [in its effect], causing the function of Liùwèi to be decreased to a lower position, losing the original intent in the design of this formula. These are the errors of later generations of mediocre physicians.
李士材曰：用此方者，有四失，地黃非懷慶則力薄，蒸曬非九次則不熟，或疑地黃之滯而減之，則君主弱，或惡澤瀉之瀉而減之，則使力薄，故歸咎於藥之無功，毋乃愚乎？
Lǐ Shìcái (1588～1655, also known as Li Zhongzi) said: in prescribing this formula, there are four common errors, dìhuáng is not of Huáiqìng region thus it’s strength is inferior. [Dìhuáng] that is not steamed and dried 9 times then it is not shú [prepared (this is because in the formula preparation it says to do this)]. Some suspect the cloying [nature] of dìhuáng [is problematic] and reduce it, thus causing the efficacy of the sovereign [herb] to be weakened. Some dislike the draining [nature] of zéxiè and then reduce it, this then decreases the strength [of the formula], then they blame the inefficacy of the herb, is that not foolish?
按：擇瀉本經云聰耳明目，為其能滲下焦之溼熱也。溼熱既除，則清氣上行，故能養五臟，起陰氣補虛損，止頭旋，有聰耳明目之功，是以古方用之，今人多以昏目疑之，蓋服之太多，則腎水過利而目昏，若古方配合，多寡適宜，未易增減也。
Áng explains: zéxiè in the classic states sharpens the hearing and brightens the eyes, yet it is used to percolate damp heat of the lower jiāo. Once damp-heat is eliminated, then clear qì is able to ascend, therefore it is capable of nourishing the five zàng, it rises the yīn qì, tonifies vacuity detriment, ceases sensations that the head is spinning, also has the effect of sharpening the hearing and brightening the eyes, thus the ancient formula use it. Now days people are confused and doubt it, then they take excessive amounts of [zéxiè], then the kidney-water is excessively disinhibited causing clouded vision. Comply with combinations in the ancient formulas, and [prescribe] the appropriate dosage, do not wilfully add or subtract!
Thanks to Leo Lok for his help on paragraphs 2 and 3, any errors that remain are my own.