Yin and Yang within Taiji

The short answer is that the question as usually asked has no answer, and that reformulating it correctly is most of the work.

The one rule

Everything in this area follows from a single point, and it is worth stating in its strongest form.

No single thing is yin or yang. Things are yin or yang relative to something else, along a specified axis of comparison. A statement of the form “X is yin” is incomplete in the way that “X is taller” is incomplete. Taller than what?

Traditional sources very often use the incomplete form, because the comparison is obvious in context to a reader inside the tradition. That is legitimate shorthand. It becomes an error when the shorthand is transmitted to readers who do not have the context, who then treat the assignment as a fixed property of the thing.

The etymology reinforces this. The two characters originally named the shaded and sunlit slopes of a hill. Neither is a substance; both are aspects of one object; and which slope is which changes as the sun moves.

The procedure

Four steps, in order.

First, identify the pair. If you have only one item, stop: there is nothing to assign. Find the other term of the comparison, and if there is not one, the question is malformed.

Second, choose the axis. This is the step almost everyone omits. Are you comparing position, motion, temperature, density, direction of change, phase in a cycle, or visibility? Different axes give different answers for the same pair.

Third, apply the axis. Along any given axis the assignment is usually straightforward and uncontroversial.

Fourth, state the comparison and the axis when you report the result. “The exterior is yang relative to the interior, in respect of position” is a usable statement. “The exterior is yang” is a fragment.

The standard axes

Traditional usage draws on a limited set of contrasts, and knowing them makes most assignments quick.

Position: above is yang relative to below; outside relative to inside; surface relative to depth.

Motion: moving is yang relative to still; fast relative to slow; expanding relative to contracting; opening relative to closing.

Thermal and luminous: hot relative to cold; bright relative to dark; dry relative to damp.

Substance: light and diffuse is yang relative to heavy and dense; formless relative to formed.

Direction of change: increasing is yang relative to decreasing; advancing relative to retreating.

Phase in a cycle: the first half of any cycle, when a quantity is growing, is yang relative to the second half.

Function and substance: this pair is used constantly in medical writing and is worth singling out. A thing can be classed as yin in respect of what it is made of and yang in respect of what it does. A standard formula describes one organ as yin in substance and yang in function, and there is no contradiction, because two different axes are in use.

Why the same thing gets opposite assignments

Once the axes are visible, apparent contradictions between sources usually dissolve.

Water is yin relative to fire in respect of temperature, and yang relative to ice in respect of motion and formlessness. Evening is yin relative to noon and yang relative to midnight, because the axis is phase in a cycle and the comparison term has changed. A junior official is yin relative to his superior and yang relative to his subordinates, because the axis is position in a hierarchy.

When two texts appear to disagree, the productive move is not to decide which is right. It is to find each one's comparison term and axis. In the great majority of cases they are answering different questions.

Nesting

The system is not a two-way sort. It is applied recursively, and this is canonical rather than a later refinement.

Classical medical writing divides a region into yin and yang, then divides the yang part again into its own yin and yang, producing expressions like the yin within the yang. Nothing prevents further subdivision, and in practice three or four levels are used.

Medical theory also uses graded terms rather than a bare binary, with three degrees on each side, forming a scheme of six. This is worth knowing because it shows the tradition itself found a simple binary inadequate for practical work.

The consequence for a reader is that the same item can be correctly described as yin at one level of analysis and yang at another, in the same document, without inconsistency. Ask which level is in play.

The relations, briefly

The four standard relations between the terms are set out fully on the page about yin and yang in the Book of Changes section. Recalled here because they bear directly on assignment: the terms are mutually defining, so neither has content alone; mutually limiting, so within any whole an increase in one is a decrease in the other; mutually generating, so each produces the other; and convertible at extremes, so a maximum is also a turning point.

The last of these has a direct practical consequence. An assignment made at an extreme is unstable, and a thing at the maximum of one term is on the point of being better described by the other. This is why traditional practitioners are cautious about assignments made at peaks.

Worked examples

Three cases, done properly.

A hot drink. Compared with a cold drink, in respect of temperature, it is yang. Compared with a hot bath, in respect of quantity and diffusion, the comparison is not useful, and the correct response is that the pair is badly chosen.

The back of the body. Compared with the front, in respect of position and exposure, it is yang in classical usage. Within the back, upper regions are yang relative to lower. So a specific point may be described as the yang within the yang, and that description is complete.

A martial arts movement. Compared with the withdrawal that precedes it, in respect of direction of change, an extension is yang. In respect of the practitioner's internal state, an outwardly expanding movement may be described as yin if attention is being gathered. Both descriptions can hold, on different axes, and the manuals often exploit exactly this.

Three-fold and five-fold schemes alongside it

One further complication is worth knowing, because it explains why the vocabulary in medical and divinatory sources is thicker than a two-term scheme would need.

Alongside the pair, Chinese technical traditions use a scheme of five terms, conventionally called the five phases, and a variety of three-fold and six-fold gradings. These are not refinements of yin and yang. They are separate systems with their own logic, joined to the pair at a later stage, and the joins are visible.

The practical consequence is that a term you meet may belong to either scheme, and the two answer different questions. The pair asks where something stands relative to something else along one axis. The five-term scheme asks which of five categories something falls into, and what its generating and restraining relations are with the others. A source that slides between them without saying so will look more systematic than it is.

A useful habit: when you meet a classification, count the terms. Two means the comparative scheme and you should look for the axis. Five means the phase scheme and you should look for the sequence. Six usually means the graded medical scheme. Eight means the trigrams. Where a source mixes counts inside a single explanation, the mixture is doing rhetorical rather than technical work.

Where the method breaks down

Three failure modes are worth recognising, and the third is the serious one.

The pair is not specified, so the assignment is empty. This is the commonest fault in popular writing.

The axis is not specified, so two sources appear to contradict each other when they do not.

And the axis is chosen after the desired answer. This is the failure that matters, because it makes the scheme unfalsifiable. If a practitioner can select from a dozen axes to justify whichever assignment supports a conclusion already reached, the assignment carries no information. The scheme has real descriptive value and no predictive power of its own, and confusing the two is where it does harm.

How to check a source

Four questions, applicable to any text that assigns yin and yang.

Does it name the comparison term? Does it name the axis? Are its assignments stable through the document, or does the same item change class without explanation? And does it use an assignment to derive a claim that could be checked independently?

A source that answers the first three well is using the vocabulary competently, whatever you conclude about its subject matter. A source that fails all three is using the words as decoration. The quickest test of all, mentioned elsewhere on this site: delete the words yin and yang from a passage and see whether any information remains.

Key points

• Nothing is yin or yang by itself; assignments require a comparison term and a specified axis.
• The four-step procedure is: identify the pair, choose the axis, apply it, and state both when reporting.
• The standard axes are position, motion, temperature and brightness, density, direction of change, phase in a cycle, and function versus substance.
• Apparent contradictions between sources almost always come from unstated differences of comparison term or axis.
• The system is recursive, and classical medicine uses graded rather than binary terms, so the same item can be yin at one level and yang at another.
• The serious failure is choosing the axis after the desired answer, which makes the scheme unfalsifiable and empty.