世 shì is a pictograph traditionally read as three tens joined together, the span of thirty years that the ancients counted as one human generation. The oldest forms show three vertical strokes, each marking a unit of ten, gathered onto a single base line, so that the whole glyph stands for thirty and, by extension, for the generation that thirty years measures. The simplified and traditional forms are identical; only one glyph exists. Its assigned radical for dictionary lookup is 一 (one), the horizontal stroke that anchors the figure.

From the image of one generation, thirty years long, the senses widen along two arcs, the human and the cosmic:

1. Generation, lineage. One human cohort succeeding the one before, and the line of descent through which a family or office passes: 世代 shìdài (generations), 后世 hòushì (later generations), 世袭 shìxí (hereditary).
2. Lifetime, an age, the life to come. A single span of life, or one of the lives a soul passes through: 一生一世 yìshēng yíshì (a whole lifetime), 来世 láishì (the next life), 今世 jīnshì (this life).
3. The world, human society. The whole sphere of living people and their dealings: 世界 shìjiè (the world), 世上 shìshàng (in this world), 人世 rénshì (the human world), 世俗 shìsú (secular).
4. An era, a period. A defined stretch of historical time: 世纪 shìjì (century), 盛世 shèngshì (a flourishing age), 当世 dāngshì (the present age).

The thread is the span of a life writ large: one generation handing on to the next, those generations stacking into eras, and the whole crowded stage of living people taken together as the world.

The root sense of 世 is the generation, the cohort that holds the world for its thirty years before passing it on. 世代 shìdài names that succession in the plural, the long file of generations stretching back and forward. 后世 hòushì looks ahead to the generations not yet born, the posterity who will judge what we leave them. 世袭 shìxí turns the line of descent into a rule of inheritance, a title or duty handed down by blood rather than chosen. Each word treats the family or the office as a relay, run not by one person but by the chain of those who stand where their parents stood.

Narrow 世 from the line of generations down to a single span and it becomes a lifetime, the one life a person is given. 一生一世 yìshēng yíshì binds 生 (a life) and 世 (a lifetime) into a vow of permanence, the whole of one's days. Touched by Buddhist thought, 世 also names one life among many: 来世 láishì is the life to come, 前世 the life before, 今世 the present one, the three woven together by rebirth. Here the same syllable that counts the dynasties of history counts the lives a soul moves through, each a single turn of the same wheel.

Open 世 to its widest setting and it names the world itself, the whole crowded stage of living people and their affairs. 世界 shìjiè, the great everyday word for the world, joins 世 (the span of living time) to 界 (a boundary), so that the world is time bounded into a place we all share. 世俗 shìsú marks what belongs to this ordinary human world rather than the sacred, the secular and the commonplace. 世故 shìgù distills the world into hard-won knowledge of how people really behave, the worldly wisdom of someone no longer naive. And stacked into long stretches, 世 gives 世纪 shìjì (the century) and 盛世 shèngshì (a flourishing age), the eras by which history measures itself.

Hold one picture at the center of 世: three tens gathered onto a single line, thirty years, the length of one human generation. That single span is the seed of every sense.

Keep the span at human scale and you get the generation: 世代 generations, 后世 later generations, 世袭 a title handed down by blood. Shrink it to one person's days and you get the lifetime: 一生一世 a whole life, and, touched by the wheel of rebirth, 来世 the life to come and 今世 this one. Now stack many lifetimes end to end and you get the era: 世纪 a century, 盛世 a golden age. Open the same word to its widest setting and it becomes the world entire, the crowded stage of all the living: 世界 the world, 世俗 the worldly, 世故 the wisdom of one who knows how the world works. Whenever you meet 世, ask which circle is meant: a generation, a lifetime, an age, or the whole turning world.