坏 splits cleanly down the middle: 坏 = 土 + 不. On the left stands 土 (tǔ), the mound of earth that marks this character as belonging to the soil, ground, and the things that crumble back into it. On the right sits 不 (bù), which carries no meaning of its own here; it lends the sound. This is a picto-phonetic of the most common type, semantic earth plus phonetic 不, and the radical 土 tells you where to file it: among walls, dust, ruins, and rot.

The simplified glyph you read today, with 不 on the right, is a modern standardization. The traditional 壞 carried a far busier phonetic, 褱 (huái), stacked above the same 土 base, and Shuōwén Jiězì defines that older form plainly as 敗也, "to be ruined, to fall apart." The throughline survives the simplification untouched: earth that gives way. A wall that slumps, a dyke that breaches, a pot fired wrong that cracks in the kiln.

From collapsing earth the sense spreads outward in two directions. Physically it becomes anything broken or spoiled: a machine that quits, fruit that softens to mush, milk that turns. Morally it becomes anything corrupt or rotten: a bad person, a wicked plan, a child who has gone astray. Mandarin keeps both alive in one syllable, so 坏 can describe a dead refrigerator and a villain in the same breath.

The fourth tone falls hard, huài, the voice dropping like the wall it names. Japanese borrowed the traditional 壞 as kai (the verb 壊れる, kowareru, "to break"), and Korean reads it goe. Across all three the image holds: something that once stood whole has come apart at the ground.

Picture a mud-brick wall after a week of rain. The 土 on the left is the wall itself, a packed mound of earth still standing. Then read the 不 on the right as the verdict the wall is about to deliver: not anymore. The clay sags, a seam opens, and the whole face slumps into a heap of crumbling soil. 坏 is the sound that collapse makes, the falling fourth tone dropping with the bricks: huài.

Hold that image and the two halves of the meaning come for free. The physical wall coming apart is 坏了, your air conditioner that quit, the leftovers gone sour. The moral version is the same collapse moved indoors: a person whose character has slumped like wet clay is a 坏人, and a child kept in bad company will 学坏, learn to fall apart the same way. Whatever crumbles, in matter or in morals, is 坏.