A hexagram consists of six lines (爻). 爻yao2 depicts the intercrossing of the long and short lines as if Yang (masculinity) and Yin (femininity) interact reflecting changes and movements in the world. Through divination they appear one after another from the bottom to the top, and are specified as line 1, line 2, .….., and line 6. The positions of lines 1 and 2 are attributed to the earthly domain; the positions of lines 3 and 4 are the human domain, and the positions of lines 5 and 6 are the heavenly domain, similarly to the lines of a trigram defined by the principle of 參san3才cai4 (see How the hexagram is formed).

The event of a hexagram develops sequentially, step-by-step and phase-by-phase, as the way it forms. The line at each position represents the status of a specific space-time in the era or the world of a hexagram.

The line moving to a position above it is called 'to go (forward)’ and is in a direction toward the future. The line moving to a position below it is called ‘to come (back)’ and is in a direction returning to the past. The past and future construct the timeline of a hexagram from the bottom to the top.

A line possesses many characteristics which determine its status and function in a hexagram. They are summarized as follows.

The line's essence and instinct

The line's essence is Yang (masculinity) and Yin (femininity). The instinct of the masculine line is brightness, largeness, rigidity, strength and firmness, etc, and the masculine tends to move. The instinct of the feminine line is darkness, smallness, softness, weakness and tenderness, etc, and the feminine tends to remain still.

While divination is involved, the line is additionally cast as the young or the old masculine / feminine. The line of the old masculine will start changing to feminine, i.e. moving toward femininity and transforming along the way, so does the line of the old feminine.

The line's virtue and ability

Every line of a hexagram has its virtue and ability. The line's virtue depends on whether it stays at a position right for it, i.e. if it lives with righteousness and acts righteously, as well as whether it is at the middle position of the upper or the lower trigram, i.e. if it possesses the principle of moderation and acts moderately. The line's ability refers to its relation with other lines. The relationships among them are available in the forms of correlating (應ying4), neighbouring (比bi3), sustaining (承cheng2) or riding over (騎qi2), and occupying (據ju4).

The right (or appropriate) position

Yang (masculinity) and Yin (femininity) have different instincts. They must occupy a position suited to them; then they can bring their talents into full play. The odd number is designated for masculinity (as Yang is presented by a solid line), and the even number is for femininity (as the broken line has two line stokes). Therefore positions 1, 3 and 5 are the places for the masculine line, and positions 2, 4 and 6 are for the feminine line.

From the perspective of the line's virtue, a line stays at the position right for it, signifying that it can act according to the norm of the hexagram where it inhabits, or what it performs conforms to the righteous course. Otherwise, it neither acts according to what should be nor complies with righteousness; it must make a correction or persist in righteousness.

The middle position (or the axle centre)

Yang (masculinity) and Yin (femininity) can be seen as two opposite ends of one subject, like two ends of a line. Though they represents two extremities, the middle position of a trigram possesses the principle of moderation and offers them an opportunity to act moderately, i.e. neither strongly nor yieldingly, or neither radically nor conservatively. The principle of moderation is the most important norm of the I Ching and it is also the central tenet of Confucian thought, called the Doctrine of the Mean (similar to the Golden Mean promoted by Aristotle).

The middle positions of the lower and upper trigrams are also seen as two axle centres of a hexagram. Usually position 5 is taken for the primary one and position 2, the secondary one. When a line occupies the primary centre, this means that it is at the core of a hexagram and possesses the dominant power.

The relationship between the lines

The lines can interact with one another through the following possible relationships:

1. Correlation (also called the corresponding relationship)

The corresponding positions of the upper and the lower trigram in a hexagram are taken for the correlative positions, for instance, positions 1 and 4 (the bottom positions of the lower and the upper trigram) where their lines correlate with each other if one is masculine and the other is feminine as shown below, or they have so-called the hostile correlation (i.e. no correlation) if they possesses the same gender. These also refer to lines 2 and 5, as well as lines 3 and 6.

Correlation means that there is an access available between these two related lines; they might influence and interact with each other, or conflict against each other. In most cases it is auspicious and helpful if a line has a correlate.

2. Neighbouring

Two lines, staying next to each other, will have either intimate or repulsive relationship. If one is masculine and the other is feminine, they will be friendly to each other. Otherwise, they are in a state of mutual repulsion (like two magnets with the same polarity repelling each other). Usually a line will be stopped by an unfriendly line if it intends to approach or pass through it, while the friendly neighbour is a booster. In addition, two neighbouring lines in different genders can create following relationships.

a. Sustaining

Sustaining signifies a feminine line staying beneath a masculine line to sustain it. As shown on the drawing, feminine line 4 sustains masculine line 5. Usually it symbolizes submission and harmony.

b. Occupying

Occupying is the same state as sustaining, only expressed the other way around, i.e. a masculine line stays above a feminine line and occupies this feminine line, like line 5 occupying line 4. Usually it represents domination and dignity.

c. Riding

Riding means a feminine line staying on top of a masculine line and riding on it, which denotes inferiority oppressing superiority. As shown on the drawing,  feminine 5 rides over masculine line 4. Usually it is an ill omen for both the feminine and masculine line.

In addition to the line's virtue and ability, each line has different status, characteristic and the mode of conduct in accordance with its position in a hexagram.

The social status

According to the position where a line stays, it is designated a social status in the times of the feudal society. From the bottom to the top, nobility and lowliness are arrayed as follows:

The 6^th line at the top position (the top line): the shrine (i.e. the symbol of a clan or a dynasty). Or in some cases, position 6 refers to a very honoured position but without any title, power, responsibility or obligation.

The 5^th line: the king.

The 4^th line: the courtier of the king, or the official of the central government, or a high-ranking official.

The 3^rd line: the feudal lord, i.e. the duke.

The 2^nd line: the courtier of the duke, or a domestic official, or a low-ranking official.

The 1^st line (the bottom line): an ordinary intellectual or a commoner.

Where divination is concerned, these six positions can be redefined according to the nature of the question. For example, if the modern political system is involved, the upper trigram can be seen as the government, and the lower trigram is the people. Its six lines can be assigned as follows:

The 6^th line: the country, or a retired official.

The 5^th line: the president.

The 4^th line: the official

The 3^rd line: the civilian leader.

The 2^nd line: the elite of civilians.

The 1^st line: the commoner.

Or if research and development is the issue, the line can be defined as:

The 6^th line: after-sales service.

The 5^th line: the product.

The 4^th line: marketing and sales.

The 3^rd line: production.

The 2^nd line: technology or know-how.

The 1^st line: material.

The characteristic and the mode of conduct

According to the position in a hexagram and the status in the feudal society, each line has different characteristic and the mode of conduct:

Lines 2 and 4 engage in the similar jobs, but are placed at different positions, signifying that they possess the same function and can attain the same achievement. Therefore line 4 can be also regarded as one who possesses plenty of good reputation. This also refers to the lines at the position 3 and 5; therefore line 3 possesses plenty of feats as well.

Among the six lines, some play a more important role in a hexagram; they are specified as the master line and the representative line.

The master line

There are two different kinds of master lines; one is called the founding line and the other, the host line.

The founding line is the one, by which a hexagram is formed, and from which the hexagram name and its significance are derived. For example, the masculinity of line 3 in the lower trigram (i.e. the lower society) of hexagram 41 is diminished and used to enrich the upper trigram (i.e. the higher society); thus, it is signified as loss.

The host line is the one that dominates the whole hexagram to fulfil the assigned mission. It is usually line 5, the one at the primary axle centre and the king’s position. However this still depends on the real situation of a hexagram. For example, line 5 of hexagram 42 sincerely and trustworthily realizes the wishes of those below in accordance with its assignment, i.e. (those above) to enrich (those below), while line 2 of hexagram 41 is seen as the one that carries out the true significance of diminution, i.e. the one below need not deliberately diminish oneself for the sake of enriching the one above.

The representative line

Among three lines of a trigram, there is one line unique or more important than the others; it is regarded as the representative line of this trigram and represents this trigram.

The unique line is the one that is minor in gender. For example, the top line of trigram Dui (joy, the marsh) is the only feminine line; thus it is the representative.

Trigrams Qian2 (perseverance, heaven) and Kun1 (submissiveness, earth) are composed entirely of either masculine lines or feminine lines. The one in the middle, i.e. at the core, is regarded as the representative.

The above rules also refer to the hexagram. If a unique line is available in a hexagram, it is taken for granted as the representative. If both the lower and the upper trigrams have a unique line, the line in the lower trigram will be the representative. If there is no unique line existing in a hexagram, then depending on the hexagram, either line 5 or line 2 can be taken as the representative. For example, line 5 of hexagrams 1 and 11 is their representative line, while line 2 of hexagrams 2 and 12 is their representative line.

Line analysis

Each line position represents a space-time continuum in the era or world of a hexagram. The line performs its role according to its instinct, virtue and ability at each particular time and position.

In the Zhou Yi, every hexagram has a subject, and each of its lines is provided with a text related to the subject. The text is mainly composed of the line's status (i.e. its environment and encounter), warning and advice, as well as judgement. Generally speaking, the line's status is illustrated in the hexagram itself or by the images of its related trigrams. The warning and advice are given according to its instinct, virtue and ability. The judgement is derived from the result of its actions, or it is an inevitable outcome as the text dictates. By means of analysis according to the above, the true significance of the text is unfolded in front of us. The analysis method can be different; the result is always the same, as all is defined in the text.

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