What Is An Immersive Sim?

The Difficulty of Definitions

Tim opens by acknowledging that definitions are inherently hard. He references his earlier video "What Is A Cup?" to illustrate that even simple physical objects resist clean definitions, and his "What Is An RPG?" video, which attempted (with limited success) to settle debates about role-playing games. He approaches immersive sims with the same caveat: this is his personal definition, and people will argue about it.

Tim Cain's Three-Part Definition

Tim defines immersive simulations (also called immersive sims or IMSIMs) as games with three core features:

Many Basic World Rules

The game world operates on general rules rather than scripted special cases. Damage types have consistent effects, attack types behave predictably, and the world follows systematic logic rather than one-off designer interventions.

Emergent Systems from Rule Interactions

Those basic rules interact with each other to produce emergent systems — outcomes that weren't necessarily intended by the designers but naturally result from the rules working together. Tim credits Will Wright as the master of creating simple rules that generate rich emergent properties.

Universal Rule Application

The player, along with everything else in the world, follows the same rules. There are no special exemptions — the simulation applies equally to all entities.

The IMSIM-RPG Continuum

Tim emphasizes that immersive sims and RPGs are not separate genres but overlapping descriptions. Having more IMSIM features makes a game more of an immersive sim; having more RPG features makes it more of an RPG. The two frequently overlap:

• An RPG with many systemic rule-based effects is also well along the IMSIM continuum.
• An IMSIM that lets players create characters with skills and backgrounds moves along the RPG continuum.

The Door Example

Tim uses a classic example from his own RPGs: getting past a locked door. The player might:

• Pick the lock with lockpicking skill and lock picks
• Find or buy the key
• Steal the key via pickpocketing
• Bribe or persuade an NPC for the key
• Lie to an NPC to obtain the key
• Kill the NPC and loot the key
• Break the lock, door, or wall
• Use a spell that affects the door's material (e.g., a warp wood spell on a wooden door)

Some of these solutions are designer-placed (the key, the lock, the NPC). Others emerge automatically from systemic rules — the spell affects anything made of wood, the door is tagged as wood, and no special scripting was needed. The latter is the IMSIM approach.

Why Tim Doesn't Call His RPGs Immersive Sims

Despite incorporating systemic design, Tim has never considered his RPGs to be immersive sims for several reasons:

• He was making RPGs before the term "immersive sim" existed.
• He used systemic rules because they made better RPGs, not because he was targeting the IMSIM label.
• His RPGs contain extensive hand-written scripts and designer-crafted dialogues — NPCs respond to specific traits and situations through deliberate scripting, not emergent systems.
• Players in his games are often exempt from world rules: they're "the chosen one" with unique powers, or they're immune to paralysis and knockouts because those mechanics aren't fun for the player. This breaks the third IMSIM criterion (universal rule application) but serves RPG design by preserving player agency.

Against Binary Thinking

Tim argues strongly against rigid, binary definitions ("this IS or ISN'T an immersive sim"). He believes treating genres as continuums is healthier because binary thinking causes players to artificially restrict what they play, ultimately only hurting themselves.

He poses a thought experiment: a pure IMSIM RPG would need a story that emerges entirely from world rules with zero designer-imposed narrative — completely emergent storytelling. Whether that's achievable, and whether it would require advanced AI, remains an open question.

References

• Tim Cain. YouTube video. https://www.youtube.com/watch?v=iSF4xuEGgWs