The shape of a mouth, thunder moving beneath a still mountain: a hexagram of nourishment. Correctness in what one feeds and how one is fed leads to good fortune.
Zhen ☳, thunder, whose quality is movement (動), lies beneath Gen ☶, the mountain, whose quality is stopping (止). Zhu Xi sees jaws in the figure: solid lines at top and bottom around an open center, the upper jaw still and the lower one moving. Yi is nourishment, and the judgment asks what one nourishes and how one feeds oneself, finding good fortune in correctness.
Judgment (卦辭)
The text attached to the whole hexagram, read when no line is changing.
頤，貞吉。觀頤，自求口實。
Yi: being correct and firm brings good fortune. Examine the nourishing, and the way one seeks one's own food.
Zhu Xi glosses yi as the jaw: the mouth takes in food to sustain the body, so the hexagram is about nourishment. Its shape is a mouth, solid lines above and below with four open lines inside, the upper jaw still and the lower one moving. Good fortune depends on correctness. Examining the nourishing means looking at what one chooses to nourish; seeking one's own food means looking at how one keeps oneself fed. In both, he says, correctness is what brings good fortune.
Image (大象)
The Image commentary (象傳) reads the whole hexagram from its two trigrams.
山下有雷，頤。君子以慎言語，節飲食。
Below the mountain there is thunder: Yi. The noble person guards speech and keeps measure in food and drink.
Thunder stirring beneath a still mountain gives the moving lower jaw and the fixed upper one. The mouth both speaks and eats, so the noble person watches both. Zhu Xi calls care in speech and restraint in food and drink the most pressing tasks in nourishing virtue and nourishing the body.
Lines (爻辭)
From the bottom line to the top. In the line names, nine (九) marks a yang line and six (六) a yin line.
Line 1, yang (初九)changing line in the shared reading
舍爾靈龜，觀我朵頤，凶。
You set aside your spirit tortoise and watch me with your jaw hanging. Misfortune.
The spirit tortoise, Zhu Xi explains, is a creature that needs no food, and a hanging jaw is the look of wanting to eat. The first line (初九) is strong enough at the bottom to need nothing from anyone. Yet it looks up to the soft fourth line, its partner, and lets appetite move it. Setting aside what is sufficient in oneself to gape at what another has is why the text sees misfortune.
Line 2, yin (六二)changing line in the shared reading
顛頤，拂經，于丘頤，征凶。
Seeking nourishment upside down goes against the norm. Seeking it from the hill, going forward brings misfortune.
The second line (六二) looks for nourishment outside itself, and both directions go wrong. Turning down to the first line reverses the proper order, so Zhu Xi calls it upside down and contrary to the norm. Turning up toward the top line, which the hill stands for since a hill is high ground, means going out to it, and that brings misfortune.
Line 3, yin (六三)changing line in the shared reading
拂頤，貞凶，十年勿用，无攸利。
Going against nourishment. Even if correct and firm, misfortune. For ten years, do not act. Nothing is favorable.
Soft, off center and out of its proper place, the third line (六三) sits at the top of the thunder trigram, where movement is most extreme. Its way of seeking nourishment runs against what nourishment is, and Zhu Xi says that once it does, even correctness cannot make it turn out well. The text adds ten years without acting and nothing favorable.
Line 4, yin (六四)changing line in the shared reading
顛頤，吉。虎視眈眈，其欲逐逐，无咎。
Nourishment turned upside down: good fortune. A tiger's stare, intent and fixed; its desire presses on and on. No blame.
Like the second line, the fourth (六四) seeks nourishment from below, from its partner in the first place, which is upside down. But both lines are correct, and the fourth relies on that support to provide for those beneath it, so even the reversal brings good fortune. Zhu Xi reads the tiger's stare as looking down with single focus, and the desire as seeking that never lapses; with that, no blame.
Line 5, yin (六五)changing line in the shared reading
拂經，居貞吉，不可涉大川。
Going against the norm. Remaining correct and firm brings good fortune. One cannot cross the great river.
A ruler is supposed to nourish others, but the fifth line (六五) is soft and out of its proper place and cannot; instead it relies on the strong top line to do so. That goes against the usual order, which is why the text speaks of departing from the norm. Staying put and keeping correct is still good, but the great river is beyond its reach.
Top line, yang (上九)changing line in the shared reading
由頤，厲吉，利涉大川。
Nourishment comes by way of it. There is danger, but good fortune. It is favorable to cross the great river.
Because the ruler leans on it, the top line (上九) becomes the one through whom everything is fed. Zhu Xi links the danger to the height of the place and the weight of the task, yet the text still finds good fortune. Strong and yang at the top, it can take on the great crossing that the fifth line could not.
If you drew this hexagram
Which text to read depends on how many lines are changing. With none, read the judgment; with one, read that line; with more, follow Zhu Xi's rules in the Yixue qimeng.
Text: Zhu Xi, Yuanben Zhouyi benyi (原本周易本義), Siku Quanshu Wenyuange copy, as transcribed by the Kanseki Repository (KR1a0031), corrected and punctuated by K-magpie. Translation and explanation: written by AI (Claude) from Zhu Xi's commentary and checked against the text and commentary. Sources and the list of corrections are on the Today's Hexagram page.
Characters corrected in this hexagram — Line 3, yin (六三): 十年勿用元攸利 → 十年勿用无攸利 · Line 4, yin (六四): 虎視耽耽 → 虎視眈眈