传 is a pictophonetic compound: the person radical 亻 carries the meaning, while 专 (zhuān) supplies the sound. The 亻 on the left marks the character as something done by or among people, and the core idea is one person handing a thing on to the next. The phonetic on the right lends mainly its pronunciation. The simplified 传 reduces the busier right side of the traditional 傳, but the left-hand person radical and the structure are the same in both forms.

From the single image of passing a thing from hand to hand, the character splits into two readings:

Read chuán the senses are verbal and outward-moving:
1. To pass on, to hand down. To carry something forward through time or along a line: 传统 chuántǒng (tradition), 传递 chuándì (to pass, to relay), 遗传 yíchuán (heredity), 流传 liúchuán (to circulate).
2. To transmit, to spread. To send a thing outward through space or a population: 传播 chuánbō (to disseminate), 传染 chuánrǎn (to infect), 宣传 xuānchuán (to publicize), 传开 chuánkāi (to spread around).
3. To convey, to impart. To deliver a message or teaching: 传达 chuándá (to convey), 传授 chuánshòu (to impart), 传唤 chuánhuàn (to summon).

Read zhuàn the sense turns nominal and literary: a written record handed down, a 传记 zhuànjì (biography) or a 经传 jīngzhuàn (classic and its commentary). The thread is the same in both readings: something carried onward from one party to another, whether a spoken word, a contagion, or a written life.

The first face of 传 chuán is carrying a thing forward through time, from one hand or one generation to the next. 传统 chuántǒng is the great noun of this sense: tradition, the body of custom handed down across generations. 传递 chuándì is the plain verb, to pass or relay an object, a message, a baton, from one point to another. Push the idea into the body and you get 遗传 yíchuán, heredity, the traits a parent passes to a child. Spread it across a whole society over time and you get 流传 liúchuán, the way a story or a song circulates and survives. All share the image of something kept alive by being handed on.

Where the first sense moves a thing forward through time, the second sends it outward through space and through a population. 传播 chuánbō is to disseminate, to broadcast a message, an idea, or a disease so that it reaches many. 传染 chuánrǎn narrows that to contagion, the spread of an illness from one body to another. 宣传 xuānchuán turns the act deliberate: to publicize, to propagate a message on purpose. Each takes the radical's image of handing a thing on and multiplies it outward to a crowd.

Shift the tone from chuán to zhuàn and the character turns from a verb into a noun: a written record handed down. A 传记 zhuànjì is a biography, the account of a life set down for posterity; tell your own and it becomes 自传 zìzhuàn, an autobiography. In the classical histories, the 列传 lièzhuàn are the chapters of collected biographies, the lives of statesmen and generals arranged one after another. The same reading names a 传 in the sense of a commentary attached to a classic, as in 经传 jīngzhuàn, "the classics and their commentaries." It even survives in famous titles: 水浒传 Shuǐhǔ Zhuàn, the great novel known in English as Water Margin, where 传 marks the work as the handed-down chronicle of its heroes.

Hold one picture at the center of 传: a person (亻) holding something out, handing it on to whoever comes next. That single gesture of passing a thing forward is the seed of every sense.

Hand it forward through time and you get the first sense, chuán as handing down: 传统 tradition, 传递 to relay, 遗传 heredity, 流传 to circulate. Hand it outward to a crowd and you get the second, chuán as spreading: 传播 to disseminate, 传染 to infect, 宣传 to publicize, 传达 to convey. Now imagine the thing being handed on is not an object or a word but a written life, a scroll bearing the story of a person, and the tone changes to zhuàn: 传记 a biography, 自传 an autobiography, 列传 the collected lives of a history. Whenever you meet 传, ask what is being passed on, and to whom, and whether the answer is an act (chuán) or a record (zhuàn).