Yang lines and yin lines represent two fundamental forces.
Tips
culture
爻 is the building block of the 八卦 (bāguà, eight trigrams) and 六十四卦 (sixty-four hexagrams) in the 《易经》. A solid line is 阳爻 (yáng yáo); a broken line is 阴爻 (yīn yáo). Stacking six gives one hexagram.
history
Almost all modern uses are tied to 易学 (Yijing studies) and divination terminology.
Top 乂 is a single pair of crossed strokes. Doubled with the matching pair below, the graph pictures the broken-and-solid lines stacked in a Yijing trigram — the basic divinatory unit that 爻 names.
Bottom 乂 repeats the upper crossed-strokes pair. The reduplication is the entire point: 爻 is two interlocking pairs of lines, captured as 'criss-cross' in the literary verb sense, and standing for an interlaced trigram line in Yijing usage.
Radical
Trigram LinesKangxi #89
A tiny radical group used mainly to index a handful of divination-related characters. Productivity is very low; the main reason a learner meets 爻 is via 爽 (shuǎng) and 爾/尔 (ěr), where it appears as a structural component rather than a meaning clue.
