2.4. Different Models for Different Purposes

Complex models are often appropriate for different purposes and interpretations:

Predictive → explanatory

Schelling’s model of segregation might shed light on a complex social phenomenon, but it is not useful for prediction. On the other hand, a simple model of celestial mechanics can predict solar eclipses, down to the second, years in the future.

Realism → instrumentalism

Classical models lend themselves to a realist interpretation; for example, most people accept that electrons are real things that exist. Instrumentalism is the view that models can be useful even if the entities they postulate don’t exist. George Box wrote what might be the motto of instrumentalism: “All models are wrong, but some are useful.”

Reductionism → holism

Reductionism is the view that the behavior of a system can be explained by understanding its components. For example, the periodic table of the elements is a triumph of reductionism, because it explains the chemical behavior of elements with a model of electrons in atoms. Holism is the view that some phenomena that appear at the system level do not exist at the level of components, and cannot be explained in component-level terms.

We get back to explanatory models in Chapter 6, instrumentalism in Chapter 8, and holism in Chapter 10

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