PSD.5:4.2 - Choose complementary contributions at the needed grain
Consider what each model can actually contribute before selecting a notation or tool.
| Needed contribution | A possible model | Limit to preserve |
|---|---|---|
| Make different interpretations and concerns discussable. | A rich picture, purposeful-activity model, or attributed cognitive map. | It expresses selected interpretations; agreement with the drawing is not agreement with an intervention or proof of a causal relation. |
| Examine a proposed mechanism or dependency. | A causal, stock-and-flow, network, or dependency model. | An arrow may be a hypothesis or structural assumption. A causal claim requires its direct evidence. |
| Explore changed conditions and intervention responses. | A scenario or conditional simulation. | A scenario is not a probability estimate; a simulated response depends on the model and inputs. |
| Expose objectives and distinguish consequences. | An objectives hierarchy, criteria model, or consequence table. | The arrangement does not supply legitimate weights, commensurability, or permission to trade one concern against another. |
| Test a technical feasibility premise. | A domain calculation or qualified engineering model. | Feasibility holds only within its configuration, operating envelope, evidence, and uncertainty limits. |
Select the smallest set that covers the material questions. A qualitative model may reveal a question worth quantifying; a numerical model may reveal a missing qualitative distinction. Neither direction is a universal order. Drop a model that supplies no distinct contribution unless its independently grounded evidence is needed to challenge another.
A concern map can already complete the task of making participants’ concerns discussable. When another material question asks what causes an outcome or what an intervention would change, use an adequate causal model directly. If the causal relations still need to be constructed or compared, C.28.CM helps turn the relevant subject knowledge and mechanism accounts into explicit models for that question. Return their assumptions, conditional consequences and unresolved alternatives to the combined account. Keep each existing model for the question it can answer; the constructed causal model still needs the claim-specific assurance in :4.5.
When the question concerns participants’ intentions, their dependence on one another and possible alternatives, the Reference’s goals-and-dependencies walkthrough develops an actors-and-goals model from a service difficulty. It explains how to select what a view reveals, turn a question into analysis assumptions, interpret the answer and return to an omitted assignment when the result exposes a conflict. Use that connected account when these joins need explanation; a sufficient existing model can be used directly.