institution/Wiki/core/Propensity.md

# Propensity — nature × nurture

Propensity is the suite's disposition engine. It answers one question and only one: *"would **this**
pawn do it?"* — never *"would a prisoner,"* never *"would a colonist."* Every behaviour in the suite
that hinges on a pawn's character comes back to this, so crime, contraband brewing, escape arming, and
gang recruitment all read the same answer instead of each guessing.

The model is deliberately old-fashioned: **nature × nurture.**

- **Nature** is a fixed property of the person — their traits. Almost nobody is strongly disposed, and
  this never changes over a pawn's life.
- **Nurture** is what the colony has done *to* them — mood, mistreatment, unmet needs, the shadow a
  sentence leaves. This is the half **you** control, and the half no other mod models.

Good conditions pull nurture down; neglect and cruelty push it up. A saint left to rot can cross the
line; a monster kept content and deterred may never act. Both of those stories are possible by design.

---

## Nature — who they are

Every pawn starts from a **baseline of 0.05** — the floor of the human condition in this model:
everyone is capable of *something*, most people barely. From there, each trait the pawn has adds or
subtracts, and the total is held to the 0–1 range (never below 0, never above 1).

### Trait weights

Traits are matched **by name**, so if a trait's mod isn't installed that entry is simply skipped.
That's how Core uses Vanilla Traits Expanded's dark traits when VTE is present without *requiring* VTE
to be installed.

| Trait | Weight | Source | Note |
|---|---:|---|---|
| Psychopath | **+0.45** | Vanilla | no empathy; the heaviest single input |
| Kleptomaniac | **+0.40** | Vanilla Traits Expanded | counted if VTE is installed |
| Bloodlust | **+0.35** | Vanilla | enjoys violence |
| Pyromaniac | **+0.30** | Vanilla Traits Expanded | counted if VTE is installed |
| Greedy | **+0.25** | Vanilla | wants more than their share |
| Abrasive | **+0.15** | Vanilla | friction with everyone |
| Ascetic | **−0.15** | Vanilla | wants little, takes little |
| Kind | **−0.30** | Vanilla | the strongest pull *down* |

Core adds no traits of its own — it reads the ones the game and your other mods already provide.
Vanilla's own dark traits count right alongside VTE's.

### Worked Nature values

Because weights simply add and then clamp, Nature is easy to read by hand:

| Pawn | Arithmetic | Nature |
|---|---|---:|
| Ordinary pawn (none of the above) | 0.05 | **0.05** |
| Kind pawn | 0.05 − 0.30 = −0.25 → clamp | **0.00** |
| A single Greedy trait | 0.05 + 0.25 | **0.30** |
| Psychopath | 0.05 + 0.45 | **0.50** |
| Psychopath **and** Kind | 0.05 + 0.45 − 0.30 | **0.20** |
| Greedy + Abrasive | 0.05 + 0.25 + 0.15 | **0.45** |
| Psychopath + Bloodlust + Kleptomaniac | 0.05 + 0.45 + 0.35 + 0.40 = 1.25 → clamp | **1.00** |

Two things fall out of this. First, the clamp isn't decorative: a Kind pawn floors at exactly `0`
(nature can never make them *disposed*, only never disposed), and a stacked monster ceilings at `1`.
Second, traits genuinely net against each other — a Kind Psychopath is a real, middling `0.20`, not a
contradiction.

Most rolled pawns sit at or near the `0.05` floor. That's intended: a colony full of ordinary people
is supposed to be mostly safe on nature alone. What makes them dangerous is nurture.

---

## Nurture — what you have done to them

Nurture is a **multiplier**. An ordinary pawn under ordinary conditions sits at **1.0**. The number
rises as things go wrong and falls as they go right. Each lever below stacks on top of the last.

### The multiplier ladder

| Lever | Factor | Applies when | Stacks? |
|---|---|---|---|
| **Despair** | ×2.5 | mood below 20% | mutually exclusive with "badly kept" |
| **Badly kept** | ×1.6 | mood 20–35% | mutually exclusive with "despair" |
| **Held & unhappy** | ×1.4 | held **and** mood below 40% | on top of the mood lever |
| **Prisonization** | × (depends on reform, see below) | the pawn has a non-zero reform score | on top |
| **Deterrence** | × (the colony's climate of order) | always (neutral 1.0 with only Core) | on top |

The two mood levers are either/or: a pawn is either in despair *or* badly kept, never both. "Held &
unhappy" is separate and multiplies again — so a mistreated prisoner in despair compounds
`2.5 × 1.4 = 3.5` before anything else. That is a badly run cell.

### Prisonization — the reform lever

The reform lever is where a sentence leaves a permanent mark. A pawn's **reform score** runs from
about −1 to +1 and turns into a multiplier:

| Reform score | Meaning | Factor |
|---:|---|---:|
| **+1.0** | fully rehabilitated | 0.50 |
| +0.5 | improving | 0.75 |
| 0 | untouched (no effect) | *1.00* |
| −0.5 | hardening | 1.25 |
| **−1.0** | prisonized | 1.50 |
| beyond +1.2 | (over-reformed) | floors at **0.40** |
| beyond −2.0 | (utterly broken) | ceilings at **2.00** |

Reform is nominally a 0-to-1 rehabilitation score, but harsh punishment can drive it **negative** —
that's the "hardened, prisonized" end. Within the realistic −1…+1 range the factor spans 0.5…1.5; the
0.4 / 2.0 limits only bite at the extremes, catching a pawn who's been endlessly punished or endlessly
rehabilitated.

Propensity only *reads* this score — nothing in Core moves it. The Justice layer's discipline and
parole are what nudge it up or down, which is how institutionalization and recidivism enter the game
without a separate mechanic. A pawn broken by a brutal prison stays broken (nurture ×1.5) after
release; a pawn genuinely reformed stays calmer (×0.5) for good. The scar rides on one number.

### Deterrence — the climate of order

The final lever multiplies by the colony's overall **climate of order**. **With only Core installed
it's neutral — a flat 1.0** — because Core by itself doesn't know what deterrence is. Install
**Institution: Justice** and it fills this in: a well-policed colony pulls the factor below 1 and
deters everyone a little; a lawless one pushes it above 1 and emboldens them. That's what makes
catching and punishing *one* pawn matter to the disposition of *the rest*.

With only Core installed, this lever does nothing, and that is correct. The technical details of how a
mod fills in deterrence are on the [Modder API](Modder-API.md) page.

---

## Would — the full roll

Nature and Nurture are ingredients. The full roll is the meal: the actual yes/no for a specific
behaviour at a specific base rate. For a given behaviour, the chance works out to:

> **chance = base rate × (0.1 + Nature × 2) × Nurture**, capped at 85%.

Three things are happening there:

1. **Base rate** is the behaviour's own dial — how likely an *average* pawn is to do this particular
   thing (a rare act uses a small number, a common one a larger). Core doesn't decide it; whichever
   system is asking does.
2. **(0.1 + Nature × 2)** is the nature amplifier. It spans **×0.1** (a saint, Nature 0) to **×2.1**
   (Nature 1). At the common `0.05` floor it's **×0.2** — so an ordinary pawn is one-fifth as likely
   as the base rate, while a maxed monster is over twice as likely — *before* nurture.
3. **× Nurture** applies circumstance on top, and the whole thing is capped at **85%** by default.
   Nobody is ever a dead certainty; there's always slack. A behaviour that wants a harder or softer
   ceiling can set its own cap.

### Worked example 1 — an ordinary colonist, content

Base rate 10%, an ordinary pawn (Nature 0.05), good mood so Nurture 1.0:

- nature term = 0.1 + 0.05 × 2 = 0.2
- chance = 0.10 × 0.2 × 1.0 = 0.02 → **2%**

Two percent — and, critically, **fixed**. For this pawn and this question it's a settled 2% coin that
either comes up or doesn't; it isn't re-flipped every moment.

### Worked example 2 — a mistreated psychopath prisoner

A Psychopath + Bloodlust prisoner (Nature 0.85), mood 15% (despair ×2.5), held and unhappy (×1.4),
reform −0.5 (hardening → ×1.25), Core-only so deterrence 1.0. Base rate 10%:

- nature term = 0.1 + 0.85 × 2 = 1.8
- nurture = 2.5 × 1.4 × 1.25 = 4.375
- chance = 0.10 × 1.8 × 4.375 = 0.7875 → **~79%**

Same base rate as example 1, same engine — but nature and a badly-run cell have turned a 2% pawn into
a near-certainty. The player did that, lever by lever.

### Worked example 3 — hitting the cap

A fully stacked monster (Nature clamps to 1.0), in despair (×2.5) and held & unhappy (×1.4), in a
lawless colony where Justice has set deterrence to 1.4. Base rate 10%:

- nature term = 0.1 + 1.0 × 2 = 2.1
- nurture = 2.5 × 1.4 × 1.4 = 4.9
- raw chance = 0.10 × 2.1 × 4.9 = 1.029
- capped at **85%**

The raw product blew past 100%; the cap reins it to 85%. Even here, a 15% sliver of "not today"
survives. That sliver is deliberate — it keeps the worst pawn a character with a bad day coming, not a
scripted event.

---

## The fixed roll — characters, not a dice cup

Each pawn's answer to "would they?" is **fixed** by two things: who the pawn is (their permanent
identity) and which behaviour is being asked about. It is not re-rolled from scratch each time. This is
the single most important design decision on this page, and it's worth being precise about why.

**Save/reload stability.** Because the answer is tied to the pawn's permanent identity and the specific
question — not to the live random stream — asking "would they?" gives the same answer before and after
a save/reload, as long as the inputs (traits, mood, reform) are the same. You can't scum a reload to
re-roll a pawn into a different person. *Who* they are doesn't shift under them on a reload.

**A character, not a moment-to-moment lottery.** If the game flipped a fresh coin every tick, any pawn
would eventually do anything if you waited long enough. Fixing the roll instead makes "would this pawn
pocket a shiv?" a settled fact about that pawn under those conditions — what makes them a character,
not a dice cup.

**Live circumstance still bites.** The roll freezes the *identity*, not the *situation*. Nurture is
recomputed live, so as mood collapses or reform hardens, the same pawn's chance climbs and the same
fixed coin can flip from "no" to "yes." The pawn who wouldn't have acted last month acts now — not
because the dice changed, but because you let their world get worse.

**Different questions, independent answers.** Each behaviour is its own separate question, so the
answers don't leak into each other: a pawn who would pocket a shiv is not therefore a pawn who would
inform on a cellmate. One pawn can be reliably one kind of trouble and reliably not another, and that
pattern is stable across the whole game.

---

*Part of the **Institution** suite.*