Every placement in a chart shows up in four ways: the light, the shadow, the excess and the deficiency. It is the same piece seen in four states, and a reading that describes only the first is paying a compliment.

The idea is simple to state and hard to apply: a quality does not come alone. It arrives with a price built in, it has a way of getting out of place by excess and it has a way of being missing. Whoever reads a chart by the four faces stops asking whether a placement is good or bad, because the question stops making sense.

• Light: what the placement develops well. The one who notices is the person themselves, and with pride.
• Shadow: what it demands from those around. The ones who notice are the people who live with it.
• Excess: what happens when it has no brake. The first to notice are the people who live with it, and then the person themselves.
• Deficiency: what is missing when it never gets to happen. Almost nobody notices, and that is the problem.

It is the competence that piece builds over a lifetime. It is neither inborn talent nor a guarantee: it is the direction in which that person's effort pays off more than it would in another.

Mars in Aries begins. It moves before being sure, and that is a real skill, most of the good things in a life depend on somebody having started without a guarantee. Venus in Taurus stays: it builds bonds that last, taste you can recognise, a room other people rest in.

The light is the easy face to write, and that is why the whole internet stops there.

The shadow is no opposite of the light: it is its cost, paid by the people around. It grows from the same root, and that is why willpower does not make it go away.

Mars in Aries begins, and, beginning, runs over whoever was still explaining. The hurry that makes it act is the same one that makes it trample, and the person almost never sees it, because to them it was just getting things done. Venus in Taurus stays, and, staying, holds on to what is already over. The loyalty that makes it dependable is the same one that keeps it in a job, a house or a relationship years past the deadline.

Notice the pattern: the shadow tends to be visible to others before it is visible to the person carrying it. It is the face that turns up in the complaint of a sibling, a business partner or a spouse, and that is what gives it practical value in a reading.

Excess is the quality working when it should not be working. The difference from the shadow: the shadow is the built-in price, and excess is a matter of dose and of place.

Mars in Aries in excess picks fights for sport. The will keeps working, and it will spend itself on whatever turns up, an argument in traffic, a retort nobody needed. The person ends the day tired from fights they did not choose. Venus in Taurus in excess turns comfort into weight: the good house becomes a house nobody leaves, and the pleasure that was rest becomes the only plan.

Mending excess is different from mending shadow, and that is why it pays to keep them apart. Shadow is managed by telling the truth to the people alongside. Excess is managed by finding where the thing has a use, because the energy is going to come out either way.

Deficiency is the placement never quite happening. The piece is in the chart, the function exists, and even so the person has no access to it. It is the fourth face, the least published of the four, and usually the one that hurts most.

Mars in Aries in deficiency cannot want. The person does not fight, does not ask, does not begin, and what shows on the outside is tiredness rather than anger. They arrive saying they have no energy, and what is there is a will that never found an exit and turned back inwards. Venus in Taurus in deficiency cannot receive: gives well, cares well, and freezes when somebody offers something in return.

Why almost nobody writes this: deficiency does not look like astrology, it looks like something else. It arrives under the name of tiredness, of bad luck, of a difficult personality. A text describing only light and shadow leaves that person with nowhere to stand, they read that they have a strong Mars, recognise themselves in none of it, and conclude that astrology does not work.

And there is a practical consequence: the same placement, in two people, can sit on opposite faces. One in excess and the other in deficiency, with the same line in the chart. No reading finds out which of the two is yours without talking to you, the chart shows the repertoire, and life shows which face the person is on right now.

The best way to grasp the difference between the four is to see the same piece in all four states. Three examples, with the Moon in Cancer coming in as the third:

Mars in Aries. In the light, it starts without waiting for a guarantee. In the shadow, it runs over whoever was explaining. In excess, it fights for sport and spends energy on small causes. In deficiency, it can't manage to want, and this comes out as tiredness.

Venus in Taurus. In the light, it creates bonds that last. In the shadow, it holds on to what has already ended. In excess, comfort becomes the only plan. In deficiency, it can't receive what is offered.

Moon in Cancer. In the light, it cares, and notices before anyone asks. In the shadow, it charges in memories for what it gave in care. In excess, it adopts other people's problems as its own. In deficiency, it doesn't ask for comfort, and falls ill from not asking.

Read the three deficiencies again: none of them seems to be about astrology, and that is exactly where most people recognise themselves.

The light and shadow astrology reading of a placement usually stops at two states: what it has of good and what it has of hard. It is a good half of the way, and it leaves out precisely the two faces in which people actually recognise themselves.

With two faces, the reading has only one question to ask: is this a quality or a flaw? With four, the question changes in nature and becomes useful, is this function in surplus or is it missing? The two answers demand opposite things from whoever is living it, and calling both of them shadow means handing the same advice to two contrary problems.

That is why, here, the light and shadow astrology reading of each sign goes through all four, and not two. The name matters less than the arithmetic: four states per placement, and the reading saying which of them the rest of the chart suggests the person is in.

Start with what repeats, and not with the flashiest piece. A quality that shows up three times by different routes, a planet, the house it sits in and the ruler of that house all saying the same thing, is a subject of the chart. One that shows up once is a detail.

Then ask, for each of those, which of the four faces you are on today. The question that settles it is usually this one: do the people close to you complain about it, or do you miss having it? The first answer points to shadow and excess; the second, to deficiency.

And the limit, said out loud: none of these faces is a diagnosis. Astrology describes tendency and gives vocabulary for what somebody already lives, it replaces no therapist, no physician and nobody's decision. What it can do is name what had no name, and a name is the beginning of any repair.

If you want that reading done on your own chart, it is one of the analyses in the catalogue, Shadow Chart goes through the four faces of the placements that repeat in your drawing. And the chart itself, with the four layers, comes before that and free of charge.

And the questions that come up most on this subject, with the short answer: