Structure

The Yi Jing symbolism is embodied in a set of 64 abstract line arrangements called hexagrams. These are each composed of six stacked horizontal lines; each line is either Yang (unbroken, a solid line), or Yin (broken, an open line with a gap in the centre). With six such lines stacked from bottom to top in each hexagram, there are 26 or 64 possible combinations and thus 64 hexagrams.

Each hexagram is considered to be composed of two three-line arrangements called trigrams (卦 guà). There are 23, hence 8, possible trigrams.

Each hexagram represents a state, a process and may represent a change happening. When a hexagram is cast using one of the processes of divination with Yi Jing, each of the lines may be indicated as moving or fixed. Moving ("old", or "unstable") lines have a polarity in the process of reversal; a full reading will consider the hexagram that would result from the lines changing polarity.

The traditional methods for casting the hexagrams use biased random number generation procedures, so the 64 hexagrams are not equiprobable.

There are a few formal arrangements of the trigrams and hexagrams with a traditional context. The bā gùa is a circular arrangement of the trigrams, traditionally printed on a mirror, or disk. Legend states that Fu Hsi found the bā gùa on the scales of a tortoise's back.

The King Wen sequence is considered the authoritative arrangement of the hexagrams.