Four yang lines surge upward: a hexagram of great strength, whose one requirement is that the strength stay correct and firm instead of running ahead of itself.
Thunder ☳, the trigram Zhen, whose quality is movement, sits above Heaven ☰, Qian, whose quality is strength: power set in motion. Zhu Xi explains that 'great' refers to the yang lines, which have grown to four and press toward the top, and he links the figure to the second month. With yang this vigorous, success needs no mention; the text stresses only that it is fitting to stay correct and firm.
Judgment (卦辭)
The text attached to the whole hexagram, read when no line is changing.
大壯，利貞。
Da Zhuang: it is fitting to stay correct and firm.
'Great' here means yang, Zhu Xi explains: four yang lines have grown up from the bottom and push toward the two yin lines at the top. With yang this strong, good fortune and success hardly need saying, so the text says one thing only: it is fitting to stay correct and firm. Strength that is already present does not need encouragement; it needs direction. The lines that follow show what happens when vigor runs ahead of correctness, and what happens when it is held in check.
Image (大象)
The Image commentary (象傳) reads the whole hexagram from its two trigrams.
雷在天上，大壯。君子以非禮弗履。
Thunder above heaven: Great Vigor. Where propriety does not lead, the noble person does not tread.
Thunder rolling above the sky is strength at full volume. Zhu Xi's whole note on the sentence is four characters: the one who overcomes himself is strong. Real vigor, then, shows as restraint: in declining to tread wherever propriety does not lead.
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
壯于趾，征凶，有孚。
Vigor in the toes. Setting out brings misfortune, and that is certain.
Toes sit at the very bottom and are what carry a body forward. A strong yang line at the base, in a season of vigor, is all push. Zhu Xi reads the closing words as a certainty: forcing ahead from the lowest place is bound to go badly. The first line (初九) shows strength that has not yet found its footing.
Line 2, yang (九二)changing line in the shared reading
貞吉。
Being correct and firm brings good fortune.
The second line (九二) is a yang line in a yin place, so by position it is not quite correct. But it is central, and Zhu Xi treats the middle as the way back to correctness: keeping to the center, it need not lose what is right. That is why these two words work as a caution as much as a verdict. Good fortune comes once correctness has been secured through the center.
Line 3, yang (九三)changing line in the shared reading
小人用壯，君子用罔，貞厲。羝羊觸藩，羸其角。
The petty person uses force; the noble person acts as if nothing were there. Even when correct, there is danger. A ram butts a fence and its horns are caught.
Too hard and off center at the height of a strong season, the third line (九三) shows two errors. The petty person simply throws his strength around. The noble person makes a subtler mistake, treating obstacles as if they were not there, which Zhu Xi calls courage carried too far. Even a correct cause is endangered by it. The ram that charges a fence and ends up with its horns stuck shows where it leads.
Line 4, yang (九四)changing line in the shared reading
貞吉，悔亡。藩決不羸，壯于大輿之輹。
Being correct and firm brings good fortune; regret vanishes. The fence breaks open, and the horns are not caught. The strength is in the axle block of a great cart.
The fourth line (九四) was the fence in front of the third, but ahead of it lie only two yielding lines, so its own fence opens and the horns go free; a great cart with a sturdy axle block can roll on. It is a yang line in a yin place, Zhu Xi notes, strength that stops short of extremes. Its verdict, he says, is the same as for the fourth line of Hexagram 31, Xian.
Line 5, yin (六五)changing line in the shared reading
喪羊于易，无悔。
The sheep slips away unnoticed. No regret.
Zhu Xi notes that the whole figure, with doubled yin at the top, resembles the trigram Dui, which supplies the sheep: soft outside, hard within. Only the fifth line (六五), yielding and central, has no urge to butt anything. Its vigor goes so easily that the loss is hardly noticed, and nothing is left to regret. He also allows 易 to mean a field's edge, a reading he finds workable.
Top line, yin (上六)changing line in the shared reading
羝羊觸藩，不能退，不能遂，无攸利，艱則吉。
A ram butts a fence. It can neither pull back nor push through. Nothing is favorable. If it accepts the hardship, good fortune.
At the top, vigor has run its course and movement is at its limit, so the ram is caught: too far in to back out, too soft by nature to break through. That soft nature is also the saving point. Because the top line (上六) is not hard, Zhu Xi says, it can treat the situation as difficult and handle it with care, and good fortune is still possible that way.
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, yang (九三): 羸其角之 → 羸其角 · image: 非禮勿履 → 非禮弗履