来书云：「良知，心之本体，即所谓性善也，未发之中也，寂然不动之体也，廓然大公也，何常人皆不能而必待于学耶？中也，寂也，公也，既以属心之体，则良知是矣。今验之于心，知无不良；而中、寂、大公，实未有也。岂良知复超然于体、用之外乎？」
性无不善，故知无不良；良知即是未发之中，即是廓然大公、寂然不动之本体，人人之所同具者也。但不能不昏蔽于物欲，故须学以去其昏蔽；然于良知之本体，初不能有加损于毫末也。知无不良，而中、寂、大公，未能全者，是昏蔽之未尽去，而存之未纯耳。体既良知之体，用即良知之用，宁复有「超然于体、用之外」者乎？
来信说：「良知是心的本体，就是所谓的性善、未发之中、寂然不动之体、廓然大公，为什么常人都不能做到而必须待学呢？中、寂、公既然属于心之体，那就是良知了。如今在心上验证，知没有不良的，而中、寂、大公实在未曾有。莫非良知竟超然于体用之外吗？」
性无不善，所以知无不良。良知就是未发之中，就是廓然大公、寂然不动的本体，是人人共同具有的。只是不能不被物欲昏蔽，所以必须通过学以去除昏蔽；然而对于良知的本体，本来不能有分毫的增损。知无不良而中、寂、大公未能完全的，是昏蔽未曾去尽、存养未曾纯熟罢了。体既是良知之体，用就是良知之用，难道还有「超然于体用之外」的东西吗？
Your letter says: 'Innate knowledge is the mind's substance — nature-good, the equilibrium before arousal, the still unmoving substance, vast impartiality. Why can no ordinary person do it, that learning is required? If equilibrium, stillness and impartiality belong to the mind's substance, they are innate knowledge. Testing on my mind: the knowing is never not good; yet equilibrium, stillness and vast impartiality are truly not there. Does innate knowledge then stand outside substance and function?'
Nature being never not good, the knowing is never not good. Innate knowledge is the equilibrium before arousal, the vast impartial still unmoving substance, commonly possessed by all. Only, it cannot escape dimming by thing-desire, hence learning to strip the dimming; yet of innate knowledge's own substance not a hair can be added or taken. Knowing never not good, while equilibrium, stillness and impartiality are incomplete — the dimming not all removed, the preserving not yet pure. The substance being innate knowledge's substance, the function is innate knowledge's function — what room for anything outside substance and function?