Composability is a phenomenon with a scope.
Some systems have constrained scope — closed-world composability, like a closed market:
- Notion blocks snap together within Notion's sandbox
- IKEA furniture pieces fit together in approved ways
- Lego bricks build anything, but only Lego-compatible structures
Bounded composition space. Constrained to approved affordances.
Other systems have large or unbounded scope — open-world composability, like an open market:
- Text files: any tool can read and write them, no vendor permission needed
- Unix pipes: combine any programs that speak text
- Lumber: build anything physics allows
Unbounded composition space. Any tool can participate without permission.
The difference is who controls the composition space.
Closed-world systems give you pieces and rules for combining them. You can build impressive things, but only within the boundaries the system defines.
Open-world systems give you substrate that any tool can work with. The composition space isn't bounded by what one vendor imagined. It's bounded by what's logically possible and what the actors in the ecosystem create.
Open-world systems have greater potential for exponential growth because the number of possible combinations grows with every new tool that can participate, not just with the combinations the original designer anticipated. More participants → more combinations → more network effects → combinatorial explosion.