# Mutagens and flying stars (/en/docs/guide/concepts/mutagen)

Where the four mutagens come from, the full ten-stem mutagen table, and how self-mutagens and flying predicates work.



*For: everyone. Code and the full method table are at the end of the page*

Mutagens carry the most important dynamic information in Zi Wei Dou Shu. On a single chart they wire
the static stars into a directed web of relationships.

## The four mutagens [#the-four-mutagens]

| Mutagen     | Key         | en-US mark | Usually read as                       |
| ----------- | ----------- | ---------- | ------------------------------------- |
| Hua Lu 化禄   | `sihuaLu`   | `A`        | Flow, gain, the origin of an affinity |
| Hua Quan 化权 | `sihuaQuan` | `B`        | Control, expansion, force             |
| Hua Ke 化科   | `sihuaKe`   | `C`        | Reputation, benefactors, mitigation   |
| Hua Ji 化忌   | `sihuaJi`   | `D`        | Obstruction, fixation, volatility     |

<Callout title="Mutagens print as letters in an English chart">
  The en-US vocabulary has no words for the four mutagens, so `mutagen` comes back as `A`, `B`, `C`,
  `D` in the order Lu, Quan, Ke, Ji. Predicate on `mutagenKey`, never on the letter.
</Callout>

## Mutagens come from the heavenly stem [#mutagens-come-from-the-heavenly-stem]

Each heavenly stem assigns four fixed stars to Lu, Quan, Ke and Ji respectively. It is a lookup
table:

| Stem   | Hua Lu    | Hua Quan  | Hua Ke    | Hua Ji   |
| ------ | --------- | --------- | --------- | -------- |
| jia 甲  | Lianzhen  | Pojun     | Wuqu      | Taiyang  |
| yi 乙   | Tianji    | Tianliang | Ziwei     | Taiyin   |
| bing 丙 | Tiantong  | Tianji    | Wenchang  | Lianzhen |
| ding 丁 | Taiyin    | Tiantong  | Tianji    | Jumen    |
| wu 戊   | Tanlang   | Taiyin    | Youbi     | Tianji   |
| ji 己   | Wuqu      | Tanlang   | Tianliang | Wenqu    |
| geng 庚 | Taiyang   | Wuqu      | Taiyin    | Tiantong |
| xin 辛  | Jumen     | Taiyang   | Wenqu     | Wenchang |
| ren 壬  | Tianliang | Ziwei     | Zuofu     | Wuqu     |
| gui 癸  | Pojun     | Jumen     | Taiyin    | Tanlang  |

<Callout title="The disagreement over geng's Hua Ke">
  Traditions differ on which star takes Hua Ke under the geng stem — Taiyin, Tianfu and Tiantong have
  all been argued for. x-iztro uses **Taiyin**, matching JS iztro.

  The `algorithm` switch **does not change the mutagen table**: the Zhongzhou school and the default
  school use the same one. To adopt a different reading, replace the table through Config's custom
  mutagen tables, which swap a stem's four assignments wholesale — see
  [Config in depth](/en/docs/guide/guides/config#custom-mutagen-and-brightness-tables).
</Callout>

## Natal mutagens [#natal-mutagens]

When charting, the **birth-year stem** is looked up in the table above and the mutagen marks are
stamped onto the corresponding stars. A chart carries exactly four natal mutagens — the mutable
stars include Wenchang, Wenqu, Zuofu and Youbi alongside the fourteen major stars, and all four of
those minor stars are always present, so the count never falls short.

## Horoscope mutagens [#horoscope-mutagens]

Beyond the natal set, every horoscope level has mutagens of its own: the decadal uses its decadal
palace stem, the yearly level uses the year's stem, and so on. They stack onto the same chart and
are the main handle for reading a horoscope.

The four returned stars are always in the order **Lu, Quan, Ke, Ji**.

## Flying stars [#flying-stars]

Palaces have heavenly stems too. Look a palace stem up in the mutagen table and you get the four
stars that palace **flies out**; then see which palaces those four stars sit in. That is a **flying
star**, and it is how the working relationships between palaces are described.

## Self-mutagens [#self-mutagens]

When a mutagen star flown out by a palace's own stem lands inside that same palace, it is a
**self-mutagen**.

In a reading, a self-mutagen means force being spent or leaking inside the palace itself — a
different character from flying into another palace.

## In code [#in-code]

### Reading the natal mutagens [#reading-the-natal-mutagens]

```python
chart = Astro().by_solar("2000-8-16", 2, "female", language="en-US")

for p in chart.palaces:
    for s in p.major_stars + p.minor_stars:
        if s.mutagen:
            print(f"{p.name} — {s.name} takes {s.mutagen}")
```

```text
wealth — general takes B
children — sun takes A
friends — moon takes C
health — fortunate takes D
```

### Reading horoscope mutagens [#reading-horoscope-mutagens]

```python
h = chart.horoscope("2024-10-1", 0)
print(h.decadal.mutagen)   # the four stars of the decadal mutagens
print(h.yearly.mutagen)    # the four stars of the yearly mutagens
```

```text
['sun', 'general', 'moon', 'fortunate']
['judge', 'rebel', 'general', 'sun']
```

For predicates use the key form `h.yearly.mutagen_star_keys` — the mutated stars' star keys, independent of translation.

### Asking whether a palace holds a mutagen [#asking-whether-a-palace-holds-a-mutagen]

```python
soul.has_mutagen(Mutagen.LU)
soul.not_have_mutagen(Mutagen.JI)
```

### Flying-star predicates [#flying-star-predicates]

```rust
let wealth = astrolabe.palace(Palace::Wealth).unwrap();

// does the Ji flown out by the Wealth palace's stem land in the Soul palace?
wealth.flies_to(Palace::Soul, &[Mutagen::Ji]);
```

```python
soul.flies_one_of_to(PalaceName.WEALTH, [Mutagen.LU, Mutagen.QUAN])
soul.not_fly_to(0, Mutagen.JI)

places = soul.mutaged_places()   # which palace each of Lu/Quan/Ke/Ji flew into; length 4
```

### Self-mutagen predicates [#self-mutagen-predicates]

```rust
soul.self_mutaged(&[Mutagen::Lu]);   // does the Soul palace self-mutate Lu
soul.self_mutaged_one_of(&[]);       // any self-mutagen at all
soul.not_self_mutaged(&[]);          // none of the four
```

Passing an empty list to `self_mutaged_one_of` or `not_self_mutaged` checks all four mutagens; pass
a subset to check only those.

### The full method list [#the-full-method-list]

| Method                        | Does                                                             |
| ----------------------------- | ---------------------------------------------------------------- |
| `has_mutagen(m)`              | Does this palace hold the given mutagen                          |
| `not_have_mutagen(m)`         | Does this palace lack the given mutagen                          |
| `mutagen_stars(ms)`           | The stars this palace's stem puts on the given mutagen positions |
| `flies_to(target, ms)`        | Do **all** the given mutagen stars land in the target palace     |
| `flies_one_of_to(target, ms)` | Does **any one** of them land there                              |
| `not_fly_to(target, ms)`      | Does **none** of them land there                                 |
| `self_mutaged(ms)`            | Does this palace self-mutate the given mutagens                  |
| `self_mutaged_one_of(ms?)`    | Does it have any self-mutagen                                    |
| `not_self_mutaged(ms?)`       | Does it lack all the given self-mutagens                         |
| `mutaged_places()`            | The palaces the four mutagen stars sit in                        |

A palace also carries a `mutagen_star_keys` field, giving directly the keys of the four stars its
stem mutates, in the order Lu, Quan, Ke, Ji; it follows a custom mutagen table when one is set.

<Callout type="warn" title="The empty-list semantics are asymmetric">
  This reproduces iztro's behaviour and is consistent across all three programming languages: with an
  empty mutagen list, `flies_to` returns `false` while `flies_one_of_to` and `not_fly_to` return
  `true`.
</Callout>

For mutagen predicates across the surrounded palaces, see
[Surrounded palaces](/en/docs/guide/concepts/surrounded).