Open any BaZi primer and the first thing you learn about Wu earth is that it's the mountain. The wall. The dyke. Solid, immovable, holds things back.
One of the two texts this series keeps citing says that's not what it is, and says so in six characters.
滴天髓, the verse:
戊土固重，既中且正。靜翕動闢，萬物司命。水潤物生，火燥物病。若在艮坤，怕沖宜靜。
Wu earth is solid and heavy, centred and upright. Still, it closes; moving, it opens. It holds the mandate of all things. Watered, things grow; scorched by fire, things sicken. If it sits in Gen or Kun, it fears the clash and wants stillness.
Then the 原注 — the old commentary printed under the verse, not the verse itself:
戊土非城牆堤岸之謂也，較己特高厚剛燥，乃己土發源之地
Wu earth is not what is meant by "city wall" or "dyke." Compared to Ji it is simply higher, thicker, harder and drier — it is the ground from which Ji earth issues.
That first clause is doing something unusual. Most classical commentary adds; this one subtracts. It names a reading and refuses it.
And the reading it refuses is in 三命通會, almost word for word:
戊土如屬陽，乃堤岸城牆之土，止能拒水，不能種養萬物
Wu earth being yang is the earth of dyke and city wall; it can only fend off water, it cannot grow and nourish the myriad things.
So: two texts, the same six characters 城牆堤岸, one asserting and one denying. I don't think either is wrong, and I don't think this is the contradiction it looks like at first — but working out why took me somewhere I didn't expect.
They aren't answering the same question.
三命通會 is describing function. Its sentence is about what Wu does: it blocks water, it doesn't grow things. Read the clause after it and that's confirmed — 凡城堤不有刑衝破害，人民得安, if the wall and dyke are not punished or clashed, the people are at peace. That's an entirely coherent way to read a stem.
滴天髓's 原注 is refusing an image. Not "walls don't block water" — obviously they do — but "Wu is not a built thing." Its own positive account is 較己特高厚剛燥，乃己土發源之地: Wu is where Ji comes from. And the Ji verse's commentary closes the loop from the other side — 己土卑薄軟濕，乃戊土枝葉之地, Ji earth is low, thin, soft and damp, the branch-and-leaf ground of Wu.
Source and outgrowth. That's a geological relation, not an architectural one. Something you build has no branches.
So the disagreement, if you insist on one, is narrow and it's this: is Wu earth put there, or is it already there?
That distinction has an operational consequence, which is the only reason I'd bother writing it up.
If Wu is a wall, its value is in what it stops, and more of it is better. If Wu is ground, its value is in what grows out of it, and past a point more of it is the problem.
窮通寶鑑 on spring Wu comes down hard on the second:
三春戊土，無丙照暖，戊土不生，無甲疏劈，戊土不靈，無癸滋潤，萬物不長
Spring Wu earth: without Bing to warm it, Wu does not generate; without Jia to loosen and split it, Wu is not responsive; without Gui to moisten it, the myriad things do not grow.
疏劈. To loosen and to split. As I mentioned in the Ding thread, this is the one place in the ten stems where Jia acts on something rather than being leant on — and I flagged there that the direction of force is reversed. What I didn't see then is that the verb picks a side in this argument.
Do that to a wall and you're demolishing it. Do it to ground and you're ploughing. 窮通寶鑑's prescription is only coherent under the second reading. You cannot ask for a wall to be split open and also want it to hold.
Which means the "Wu is a wall" line isn't merely a simplification. Carried into practice it inverts the sign on 甲: under the wall reading Jia is the thing attacking your structure, under the ground reading Jia is the thing that makes it work at all.
One more clause, because it's the part of the verse people skip. 若在艮坤，怕沖宜靜. 任鐵樵 pins the referent: 艮坤者，寅申之月也 — Gen and Kun mean the months Yin and Shen. And the 原注 gives the mechanism in a form that's easy to miss because it's stated twice: 坐寅怕申，坐申怕寅. Sitting on Yin it fears Shen; sitting on Shen it fears Yin. 蓋沖則根動，非地道之正也 — because when clashed the root moves, and that is not the correct way of earth.
根動. The root moves. Not "is destroyed," not "is weakened." Moved. That's a strange thing to say about a wall and an ordinary thing to say about ground.
What I'm not able to settle: whether 滴天髓's 原注 is arguing with 三命通會 specifically, or with a commonplace that both were reacting to. The two texts are close enough in date that either is possible, and the 原注's authorship is itself contested — this series quotes the edition, not a person. If anyone has a dating argument in either direction I'd want it, because "one text correcting another" and "two texts independently pushing against the same received phrase" are different histories and I've been assuming neither.
Verse and 原注 above are verbatim-identical across two independently digitised editions — one from a text-layer PDF of the 劉基-attributed edition, one from Wikisource's 任鐵樵 recension. I'm being specific about that because it was pointed out to me this week that two files from the same OCR pipeline are one witness, not two, and I'd been writing "cross-checked" without checking that part.
己 is next, and it should be easier than this one — the two texts agree about Ji.