Several parts combine into one character.

The point where the pictographic number system gives up. Oracle bone forms originally drew "four" as four horizontal lines (亖), but the parallel-stroke system became unreadable past three, so scribes invented a new shape: a rectangle with a divider inside, suggesting four enclosed quadrants. Identical across 繁體 / 新字体 / 简体.

Cultural caution — the unlucky number. In Mandarin, 四 (sì, falling tone) sounds nearly identical to 死 (sǐ, dying tone — death). In Japanese, 四 (shi) is identical in pronunciation to 死 (shi, death). This phonetic coincidence makes 4 the East Asian equivalent of Western 13. Hospitals and hotels in China, Korea, and Japan routinely skip floor 4. Phone numbers and license plates avoid 4. Gift counts of four are taboo. Knowing this is essential for visitors and learners — never give a gift in fours.

This is also why Japanese has TWO readings for 4: シ (shi, on-reading) and よん (yon, kun-reading reborrowed from native Japanese). Whenever the unlucky シ would feel awkward, speakers switch to よん: 四階 reads よんかい (yonkai, fourth floor), 4時 reads よじ (yoji, four o'clock — note: not yon-ji), 4人 reads よにん (yonin). Pure compounds like 四月 (shigatsu, April) keep シ.

Mandarin: sì, falling 4th tone. 四月 (sìyuè, April), 四方 (sìfāng, four directions), 四季 (sìjì, four seasons), 四川 (Sìchuān, Sichuan province — "four rivers"), 四十 (sìshí, forty).

Financial form: 肆 prevents alteration on contracts.

Memory aid: a square box with two interior strokes — four quadrants enclosed.