Kusamakira naku kodo yo

The expression “Rotten wood cannot be carved” names the limit of instruction when a learner’s conduct gives no grounds for confidence. Spoken by Confucius after Zai Yu sleeps during the day, it joins an image of material that cannot be worked to a reconsideration of how words and deeds should be judged: Confucius says that Zai Yu’s example changed his former habit of believing what people said about their conduct.

The rebuke and its images

The occasion is starkly specific: Zai Yu is asleep during the daytime. Confucius responds with two linked comparisons. Rotten wood cannot be carved; a wall made of dirty earth cannot receive the trowel. The paired images present the failure not as a deficiency in a particular lesson or tool, but as resistance in the material to being shaped. Confucius then turns from the images to Zai Yu, asking what use reproving him would serve.

The expression’s force comes from that progression. The first image makes carving futile; the second repeats the judgment through another craft, with a surface that will not take plaster. The verbal parallel leaves little room for an expectation that more correction alone will produce improvement. Yet the rebuke is directed at a particular response to instruction, not set out as a general account of every student or every failure.

Conduct and the loss of trust

Confucius follows the rebuke with a statement about his own changed practice. Formerly, he says, he heard what people said and trusted their conduct; now he hears their words and looks at their conduct. He identifies Zai Yu as the person from whom he learned to make this change. The episode therefore gives the insult an additional consequence: the daylight sleeping is not merely an occasion for criticism but evidence that leads Confucius to revise how he judges claims about character.

That revision makes the scene more than a proverb about teaching. Words are no longer sufficient evidence of action; conduct must be observed. The expression’s hard metaphor and the teacher’s stated change work together, setting the apparent possibility of moral formation against the need to test professions by what a person actually does.

A maxim within a wider ethical vocabulary

The book places this episode among sayings and exchanges concerned with the relation between principle and conduct. Confucius argues elsewhere that if a ruler’s personal conduct is correct, government proceeds without orders, while an incorrect example makes commands ineffective. He also insists that names must be rectified before speech, affairs, ritual, and punishments can proceed properly. These passages are not explanations of the expression, but they share its attention to whether words and formal instruction are borne out in action.

The image also stands in contrast to the book’s emphasis on sustained moral effort. Confucius describes the superior person as examining sight, hearing, demeanor, speech, work, doubt, anger, and gain with care; he praises those who pursue what is good as if they could not reach it. Against that discipline, Zai Yu’s sleeping in the daytime becomes a pointed instance of conduct that frustrates correction. The expression endures in the text as a compact, severe judgment, while its surrounding explanation preserves the lesson Confucius draws from the incident: assess people not by their words alone, but by their behavior.