According to the numbers, 6, 7, 8 and 9 (pieces of yarrows), obtained during divination, a hexagram is formed through its lines appearing, one after another, from the bottom to the top. 7 and 9, as well as 6 and 8 represents the young and the old masculine (line), as well as the old and young feminine (line), respectively.

Basically, the images that construct the oracle of a hexagram are abstract, and they vary in accordance with question concerned and people involved, as well as time and place related. Therefore the phenomenon created by its images is mutable, and a hexagram can be extensively paraphrased. However, when the hexagram in the I Ching is referred to, its images are limited to a certain category confined by its name, and interpretation must conform to its text.
　

The lower and the upper trigram

A hexagram is constituted by two trigrams, the lower trigram (also called the internal trigram) and the upper trigram (also called the external trigram). These two can be either the same or different.

In addition to their images creating phenomenon, they can also present a hexagram in many other ways, for instance, the internal trigram denotes its instinct, and the external one exhibits its disposition; the internal trigram denotes its talent, and the external one exhibits its performance; the internal trigram reflects its intention, and the external one indicates the environment. From the viewpoint of the social ranking, the space-time continuum, etc, the lower trigram represents those below, and the upper one is those above; the lower trigram represents the beginning, and the upper one is the ending; the lower trigram represents the cause, and the upper one is the effect.

Besides the lower and the upper trigram of a hexagram, its related hexagrams described below can also provide us with multidimensional understanding.

The inner (or nuclear) hexagram (called in Chinese: 互hu3卦gua4 )  

The inner hexagram is constructed of the inner lower and inner upper trigram of the original hexagram in the form of 互. The inner lower trigram is a trigram built by lines 2, 3 and 4 of the original hexagram; the inner upper trigram is built by lines 3, 4 and 5.

Hu Gua was invented by the scholars of the Han dynasty (202 B.C. to 220 A.C.) for drawing images from the original hexagram to understand its motivation, behavioural tendency, latent crisis, or winning factor, etc. Additionally the phenomena described in the line text can be also traced out through the image of the inner trigram.

The reverse hexagram (called in Chinese: 綜zong卦gua4)

The reverse hexagram is a hexagram which is upside down against the original one.

In the sequence of 64-hexagram most of the paired hexagrams  appear in the reverse form, suggesting that an event is complete only after it goes through a cycle as indicated below. Zong in Chinese means to put gather and summarise. The use of Zong Gua was initiated by Master Lai Zhi De (來知德 1562 A.C. to 1609 A.C.) of the Ming dynasty. The reverse hexagram can provide an opportunity to understand a hexagram from an integral view.

The changing hexagram (變bian4卦gua4, also called in Chinese:  錯cuo4卦gua4, or之zhi卦gua4)

When all the lines of a hexagram change to the other gender, its changing hexagram forms. They can be seen as the opposite of each other. While positioned side by side, these two are accessible to each other through their masculine and feminine lines at the corresponding positions. Therefore it is also called 錯cuo4卦gua4; 錯 means to intersect. Viewed from their interchange, they are seen as the causation of each other.

In process of divining, a hexagram might form with moving line (i.e. the old masculine or feminine line). Depending on the reading method, i.e. either all moving lines are taken into account, or only the significant one, the moving line can change (to the other gender). The hexagram which forms after change is also called the changing hexagram or 之zhi卦gua4. Zhi means to go from one position to the other, like a line moving forward or backward to another position in a hexagram, or like a hexagram transforming to another, either forward to the future or backward to the past. Hence, Zhi Gua usually suggests 1) the possible tendency, develop-ment, or outcome, etc. (if the advice of the original hexagram is followed or ignored), or 2) the original state, or the cause for what happened, etc., or 3) the current action required for what is advised to do.
　

The reciprocal increase and decrease between the masculine and the feminine line in a hexagram

A very important concept in respect to the relationship between the masculine and feminine line in a hexagram is their reciprocal increase and decrease. When one increases, it will cause the replacement of the other. The masculine replacing the feminine is called masculinity subduing (息xi2) femininity; on the other hand, the feminine replacing the masculine is called femininity overpowering (消xiao) masculinity.

A typical example of the reciprocal increase and increase between the masculine and feminine line, like moon phases, is demonstrated by the twelve-month hexagrams as indicated below

The months denoted by the above 12 hexagrams are referred to as the lunar ones. They are either 29 or 30 days in length and in a regular sequence. Chinese lunisolar calendar integrates them with 24 terms of a solar year by inserting an intercalary month every four years.

As the winter solstice always falls in November, where the dark (feminine line) will decrease after the bright (masculine line appears and) starts to increase, Fu (24) is taken for November. The season will change from winter to spring and then summer with increasing daylight (masculinity). Therefore Lin (19) is December; Tai (11), January; Da Zhuang (34), February; Guai (43), March, and Qian (1), April.

When the dark (feminine line appears and) starts to increase, the bright (masculine line) will decrease. The season will change from summer to autumn and then winter with increasing darkness (femininity). Therefore Gou (44) is May (where the summer solstice is); Dun (33), Jun; Pi (12), July; Guan (20), August; Bo (23), September, and Kun (2), October.