Where the shape comes from
The simplest graph in the script: one horizontal line, a single tally stroke, with 二 and 三 built by adding more of the same. As a heading it gathers characters whose frame rests on or hangs from a long horizontal — 上, 下, 不, 三, 世 — which is a matter of filing rather than of meaning.
汉字 filed under 一
- 上shàng (fourth tone, falling)above, upper, on top of; to go up, to get on, to attend; last, previous (上个月)3
- 下xià (fourth tone, falling)below, under, lower; to go down, to get off; to fall (of rain or snow); next (下个月)3
- 不bù (fourth tone, falling)not, no — the general negative, placed before verbs and adjectives4