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simgrammar the grammar of simulation

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Short 5: The refrigerator knows, opening frameplay · 0:36
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short 5 0:36

The refrigerator knows

transcript

In The Sims, the knowledge of how to eat is stored in the refrigerator.

Every object advertises what it offers. The refrigerator advertises Hunger, the bed Energy. A Sim weighs the offers in reach against what it needs and picks one, and the object brings the script and the animation [1].

Expansions taught Sims new things largely by selling them new objects.

It also meant every behavior was made by hand. The base game shipped with more than 150 objects, and the dataset scores the method 4 out of 5 for authoring cost.

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definition

Owns per-object interaction definitions: each interaction carries advertisements (which needs it satisfies and by how much), availability checks, distance attenuation, and the behavior script the agent runs. Agents carry no knowledge of how to use things; when choosing, an agent gathers advertisements from reachable objects, scales them by its needs, personality, and distance, selects one, and runs that object's script. In The Sims, per Forbus and Wright's notes, advertisements cover nine motives, can scale with personality points, attenuate with distance through high, moderate, low, or none presets, and check trees hide unavailable interactions; a toilet advertises 0-70 Bladder. Because behavior lives in objects, new objects add new behaviors without changing agent code, which suits expansion packs and mods. Inputs: objects in range, agent needs. Outputs: candidate actions, need restoration, animations.

player experience

Buying or placing an object changes what agents want to do, so the player designs behavior through the environment. Players learn that a better object pulls agents across the room and use placement to steer them.

design levers

  • advertised magnitude per need and whether it scales with personality or object quality
  • distance attenuation curve per interaction
  • advertised versus delivered value, which allows deceptive or broken objects
  • availability and permission checks such as ownership, age, and room
  • how many agents one object can serve at once

failure modes

  • An over-tuned advertisement makes one object a magnet that agents queue for regardless of need.
  • Assuming honest advertisements breaks when objects fail, producing loops of agents repeatedly using broken objects.
  • Attenuation errors make agents walk past nearby options to distant ones.
  • Behavior spread across hundreds of objects is harder to debug than one agent controller.

dynamics

  • Each new object adds behaviors, so the behavior space grows with content packs, which is how The Sims expansions extended play.
  • Players use objects as lures to route agents, coupling placement to behavior.
  • Scarce objects create queues and conflicts when several agents select the same one.

open questions

  • Can generative models author new objects with consistent advertisements, scripts, and animations, turning content packs into runtime generation?
  • Should language-model agents read object affordances as numeric advertisements, as text descriptions, or both?

appears in

the paper, 2 sections · 4 chapters · 3 episodes · 1 short
paper

4. A grammar of simulation games

linked in this section of the paper

paper
paper

5. The structure of the design space

linked in this section of the paper

paper
glossary

Glossary of mechanics

listed under agents & behavior, with its summary

book
ch 3

Chapter 3. Old parts

named in the text

book
ch 6

Chapter 6. Five ceilings

named in the text

book
ch 8

Chapter 8. Where AI lands

named in the text

book
ch 9

Chapter 9. Vacant lots

linked from the text

book
ep 3

Families across genres

on screen at 4:02 odd couples

episode
ep 5

The five ceilings

on screen at 0:45 behavior that lives in objects, 6:26 lifting one ceiling spends another

episode
ep 8

Vacant lots

on screen at 1:12 packages

episode
short 5

The refrigerator knows

0:36 · on screen in the short

short

sources

1
Kenneth D. Forbus, Will Wright (2001-05-31). Some notes on programming objects in The Sims. Qualitative Reasoning Group, Northwestern University (course notes)

provenance

runs in log/runs
2026-10-24
created2026-10-24-taxonomy-m3taxonomy