来书云：「人之心体本无不明，而气拘物蔽，鲜有不昏；非学、问、思、辨以明天下之理，则善、恶之机，真、妄之辨，不能自觉；任情恣意，其害有不可胜言者矣。」
此段大略似是而非，盖承沿旧说之弊，不可以不辨也。夫问、思、辨、行，皆所以为学，未有学而不行者也。如言学孝，则必服劳奉养，躬行孝道，然后谓之学；岂徒悬空口耳讲说，而遂可以谓之学孝乎？学射则必张弓挟矢，引满中的；学书则必伸纸执笔，操觚染翰。尽天下之学，无有不行而可以言学者，则学之始固已即是行矣。笃者，敦实笃厚之意。已行矣，而敦笃其行，不息其功之谓尔。盖学之不能以无疑，则有问，问即学也，即行也；又不能无疑，则有思，思即学也，即行也；又不能无疑，则有辨，辨即学也，即行也。辨既明矣，思既慎矣，问既审矣，学既能矣，又从而不息其功焉，斯之谓笃行。非谓学问思辨之后，而始措之于行也。
是故以求能其事而言谓之学，以求解其惑而言谓之问，以求通其说而言谓之思，以求精其察而言谓之辨，以求履其实而言谓之行：盖析其功而言则有五，合其事而言则一而已。此区区心、理合一之体，知、行并进之功，所以异于后世之说者，正在于是。
今吾子特举学、问、思、辨，以穷天下之理，而不及笃行，是专以学、问、思、辨为知，而谓穷理为无行也已；天下岂有不行而学者邪？岂有不行而遂可谓之穷理者邪？明道云：「只穷理便尽性至命。」故必仁极仁而后谓之能穷仁之理，义极义而后谓之能穷义之理。仁极仁则尽仁之性矣，义极义则尽义之性矣，学至于穷理，至矣，而尚未措之于行，天下宁有是邪？是故知不行之不可以为学，则知不行之不可以为穷理矣，知不行之不可以为穷理，则知「知、行」之合一并进，而不可以分为两节事矣。
夫万事万物之理，不外于吾心；而必曰穷天下之理，是殆以吾心之良知为未足，而必外求于天下之广，以裨补增益之，是犹析心与理而为二也。夫学、问、思、辨、笃行之功，虽其困勉至于人一己百，而扩充之极，至于尽性、知天，亦不过致吾心之良知而已；良知之外，岂复有加于毫末乎？今必曰穷天下之理，而不知反求诸其心，则凡所谓善、恶之机，真、妄之辨者，舍吾心之良知，亦将何所致其体察乎？吾子所谓气拘物蔽者，拘此蔽此而已。今欲去此之蔽，不知致力于此，而欲以外求，是犹目之不明者不务服药调理以治其目，而徒伥伥然求明于其外；明岂可以自外而得哉？任情恣意之害，亦以不能精察天理于此心之良知而已。此诚毫厘千里之谬者，不容于不辨，吾子毋谓其论之太刻也。
来信说：「人的心体本无不明白，但被气禀所拘、物欲所蔽，少有不昏暗的；若不靠学、问、思、辨以明了天下之理，那么善恶的机微、真妄的分辨，便不能自觉；任情恣意，其害处有说不完的。」
这一段大似是而非，是承袭旧说的毛病，不能不辨。问、思、辨、行都是所以为学，没有学了而不行的。譬如学孝，必须服劳奉养、躬行孝道，然后才叫作学；岂是悬空口耳讲说，便可以叫作学孝吗？学射必须张弓挟矢、引满中的；学书必须伸纸执笔、操觚染翰。尽天下之学，没有不行而可以称为学的，那么学之始就已经是行了。笃，是敦实笃厚的意思。已经行了，又敦笃其行、不停息其功夫，如此而已。学不能没有疑问，于是有问，问就是学，就是行；又不能无疑，于是有思，思就是学，就是行；又不能无疑，于是有辨，辨就是学，就是行。辨已明、思已慎、问已审、学已能，又从而功夫不息，这才叫笃行。并不是学问思辨之后，才放到行上去。
所以，就求能其事而言叫作学，就求解其惑而言叫作问，就求通其说而言叫作思，就求精其察而言叫作辨，就求履其实而言叫作行：分析其功夫而言有五件，合并其事而言只是一件。我的心理合一之体、知行并进之功，之所以异于后世的说法，正在于此。
如今您特别举出学、问、思、辨以求穷天下之理，却不提笃行，这是专把学问思辨当作知，而把穷理看作无行了。天下岂有不行的学者？岂有不行而可以称为穷理的？程颢说：「只穷理便尽性至命。」所以必须仁到极仁然后才叫能穷仁之理，义到极义然后才叫能穷义之理。仁到极仁便尽了仁之性，义到极义便尽了义之性。学到了穷理，算是到了顶点，却还没有放到行上去，天下哪有这样的道理？所以知道不行不足以称为学，就知道不行不足以称为穷理；知道不行不足以称为穷理，就知道知行合一并进，不可分作两截事了。
万事万物之理，不外于我心；却一定要说穷天下之理，这大概是以为我心的良知还不够，必须向外求于天下之广，来补贴增益它，这仍是把心与理分作二。学问思辨笃行的功夫，即使困勉到人一己百的地步，扩充到极处，至于尽性知天，也不过是要致我心的良知而已；良知之外，难道还有分毫可加的吗？如今一定要说穷天下之理，却不知道反求于心，那么凡所谓善恶之机、真妄之辨，离开我心的良知，又到哪里去体察呢？您所谓气拘物蔽，拘的蔽的正是这个。如今要除去这遮蔽，不在 这上下功夫，却想向外求，就像眼睛不明的人不服药调理治眼睛，只是徒然向外求明；明难道可以从外面得来吗？任情恣意的害处，也只是不能在此心的良知上精察天理罢了。这真是毫厘千里之谬，不能不辨，您不要说这议论太苛刻。
Your letter says: 'The mind's substance is never unclear in itself, but confined by endowment and veiled by desires few escape dimness; without study, inquiry, thought and discrimination to illumine the world's principles, the springs of good and evil, of true and false, cannot be self-known; to follow feeling and whim works uncountable harm.'
This passage is near-truth and yet not truth, heir to the old defect; it cannot pass unexamined. Inquiry, thought, discrimination and action are all learning; there is no learning without action. To learn filial piety one must serve and support, practice it in person — could empty talk of mouth and ear count as learning it? To learn archery one must bend the bow, nock the arrow, draw full and hit the mark; to learn writing, spread paper, take brush, apply ink. Of all learning under heaven none is learning without doing: the moment learning begins, action has begun. Earnestness means solid and unwearied: already acting, and making the acting firm, the work unceasing. Doubt breeds inquiry — inquiry is learning, is action; doubt again, thought — thought is learning, is action; doubt again, discrimination — discrimination is learning, is action. When discrimination is clear, thought careful, inquiry sifted, learning mastered, and still the work does not cease — that is earnest practice. Not that after study, inquiry, thought and discrimination the deed is then appended.
Thus: seeking ability in the affair is called study; seeking release from doubt, inquiry; seeking coherence, thought; seeking fineness of discernment, discrimination; seeking to tread the substance, action. Analyzed, five; in the affair, one. Here my unity of mind and principle, the joint advance of knowledge and action, parts ways from later doctrine.
You now single out study, inquiry, thought and discrimination to exhaust the world's principle and omit earnest practice — assigning them all to knowledge and treating the exhausting of principle as devoid of action. Is there under heaven a learner who does not act? One who without acting could be said to exhaust principle? Cheng Hao said: exhausting principle alone, one fulfills nature and arrives at the Mandate. Only humaneness utterly humane deserves the name of exhausting humanity's principle; only rightness utterly right, rightness's. Utterly humane, human nature is fulfilled; utterly right, rightness's nature is. Learning that reaches the exhausting of principle has reached its top — and still not set into action: is there such a thing under heaven? Knowing that without action there is no learning, one knows that without action there is no exhausting of principle; knowing that, one knows knowledge and action advance as one and cannot be cut in two.
The principles of the myriad things lie not outside my mind; yet one must say 'exhaust the world's principle' — as if my mind's innate knowledge were insufficient and must be patched from the world's breadth without: again mind and principle made two. The work of study, inquiry, thought, discrimination and earnest practice — even pushed through hardship a hundredfold, expanded to fulfilling nature and knowing Heaven — is nothing beyond extending my mind's innate knowledge; beyond innate knowledge, is a hair's breadth to be added? To insist on exhausting the world's principle without turning back to the mind: the springs of good and evil, the dividing of true and false — leaving the mind's innate knowledge, where would one examine them? Your 'confined by endowment, veiled by things' confines and veils precisely this. To remove the veil yet not work here, seeking outside — like a man with failing sight who will not take medicine to cure the eye but gropes abroad for brightness: can brightness be fetched from outside? The harm of following whim is likewise nothing but failing to examine heavenly principle finely in this mind's innate knowledge. Here is the hair that becomes a thousand miles; it cannot go unexamined — do not call the argument too severe.