AN OVERVIEW OF THE FOUR CORNER CODING SYSTEM
The Four Corner System has been used for many years in China and Japan for
classifying kanji. In China it is losing popularity in favour of Pinyin
ordering. Some Japanese dictionaries, such as the Morohashi Daikanwajiten
have a Four Corner Index.
The following overview of the system has been condensed from the article "The
Four Corner System: an introduction with exercises" by Dr Urs App, which
appeared in the Electronic Bodhidharma No 2, February 1992, published by the
International Research Institute for Zen Buddhism, Hanazono College. (More
examples will be added from that article in due course.)
1. Stroke shapes are divided into ten classes:
0 LID 亠
1 HORIZONTAL LINE 一
2 VERTICAL LINE ｜
3 DOT 丶
4 CROSS 十
5 SKEWER キ
6 BOX 口
7 ANGLE 厂
8 HACHI 八
9 CHIISAI 小
2. The Four Digits are derived from the Four Corners in a Z-shaped order.
A B 7 1 7 7
for example: 原 月
C D 2 9 2 2
Some examples: 仕 2421 行 2122 歴 7121 魚 2733 詞 0762 同 7722 橋 4292
3. A shape is only used once. If it fills several corners, it is counted as
zero in subsequent corners.
Some examples: 口 6000 首 8060 分 8022 大 2003 和 2690 品 6066 京 0096
4. When the upper or lower half of a character consists of only one (single
or composite) shape, it is, regardless of its position, counted as a left
corner. The right corner is counted as zero.
Some examples: 立 0010 由 5060 雪 1017 方 0022 庭 0024 糸 2090 手 2050
5. When there is no additional element to the four sides of the characters
口, 門, 鬥 (and sometimes 行), whatever is inside these characters is taken
for the lower two corners.
Some examples: 問 7760 囚 6080 國 6015 目 6010 開 7744 面 1060 銜 2110
6. The analysis is based on the block-style handwritten kaisho (楷書) shape
of characters.
(This needs attention, as 戸 is 3027, not 1027. The top stroke is treated as
a 丶.)
7. Some points to note when analyzing shapes:
o Shape 0:
When the horizontal line below a DOT shape (number 3) is connected to another
stroke at its right-hand end (as in 宀 戸, etc.) it is not counted as a LID
(number 0) but as a DOT.
Examples: 安 3040 神 3520 祈 3222
o Shape 6:
Characters such as 皿 and 尸 where one of the strokes of the square extends
beyond it, are not considered to be square (number 6) shapes, but corners
(number 7).
Examples: 且 7710 所 3222 皿 7710 館 8377 宜 3010
o Shape 7:
Only the cornered end of corner shapes (number 7) is counted as 7.
Examples: 区 7171 斤 7222 句 2762 反 7124
o Shape 8:
Strokes that cross other strokes are not counted as shape number 8 (八).
Examples: 美 8043 関 7743 大 4003 失 8043 衡 2143 尖 9043
o Shape 9:
Shapes resembling shape 9, but featuring two strokes in the middle (as in the
top part of 業 or 叢) or two strokes on one side (as in 水 or the bottom part
of 慕) are not considered as 9 shapes.
Examples: 慕 4433 業 3290 叢 3214
8. Some points to note when choosing corners.
- when a corner is occupied by more than one independent or parallel strokes,
the one that extend furthest to the left or right is taken as the corner,
regardless of how high or low it is.
examples: 非 1111 倬 2124 疾 0013 帝 0022 社 3421 猛 4721
- if there is another shape above (or, at the bottom of the character, below)
the leftmost or rightmost stroke of a character, that shape is given
preference and is taken as the corner.
examples: 察 3090 幸 4040 甼 6020 女 4040 禮 3521 其 4480
- when two composite stroke shapes are interwoven and each could be regarded
as a corner, the shape that is higher is taken as the upper corner, and the
lower stroke as lower corner.
- when a stroke that slopes downwards to the left or right is supported by
another stroke, the latter is taken as the corner.
examples: 碓 2740 裏 0073 硝 1962 薜 4464 茎 4410 被 3424
- a left slanting stroke on the upper left is taken for the left corner only;
for the right corner one takes a stroke more to the right.
examples: 身 2740 牟 2350 鴨 6752 的 2762 旬 2762 島 2772
9. Shape variations: (Dr App includes several pages of examples)
10. The fifth corner:
In order to differentiate between the several characters with the same code,
an optional "fifth corner" is sometimes used. This is, loosely, a shape above
the fourth corner which has not been used in any other shape.