MMP.Preface:2 - Problem and forces - Choose what the model must retain
A model can answer a mathematically well-formed question that differs from the one the work needs. This often happens before calculation: a convenient variable excludes an allowed arrangement, a mean hides a distinction needed for action, or a fitted relation describes observation while the question concerns an intervention.
Several choices therefore shape the construction:
| Working tension | Consequential choice |
|---|---|
| A familiar representation and the intended objects | Which distinctions must variables, domains and conditions preserve? |
| Supported structure and an unknown relation | What may vary, and what must remain true throughout that variation? |
| An event and its recorded description | Which unobserved, selected or combined alternatives can produce this record? |
| Knowing a circumstance and choosing before it is known | Which information may the instruction actually use? |
| A detailed account and an affordable answer | Which eliminated contribution needs reconstruction, approximation or a bound? |
| Resolving every unknown and settling the present question | Which remaining differences can change the required consequence? |
| Stable recovery and added assumptions | What variation does a restriction suppress, and could the requested target depend on it? |
| An uncertainty label and the claim it supports | Is the needed result a coverage guarantee, a posterior probability or a prediction for a new outcome? |
| Agreement in one use and a changed use | Which premise, mechanism or interpretation must be reconsidered? |
The requested answer determines how far to develop the model. A bound can settle a threshold question while leaving parameters unresolved. A proposal for a new working method can instead require distinctions that an earlier prediction ignored. C.11.DUA helps decide whether another calculation, observation or refinement is worth its possible contribution.