Economists can be philosophical realists about their models even though these describe
imaginary situations (von Thünen was a realist about his simplest model of the Isolated
State). This is because it is possible that the mechanisms in operation in those
imaginary situations are the same as, or similar to, those in operation in real situations.
A model captures significant truth if it contains a mechanism that is also operative in
real systems. This significant truth can be attained thanks to the false idealizations
employed by the model. Capturing this truth does not require any de-idealization by
way of relaxing those assumptions.
Unrealisticness in models is not intrinsically a bad thing. It is often a very good thing. It
may even be necessary for achieving important epistemic goals. Unrealistic
assumptions must be assessed in relation to their functions in modeling (such as fixing
a causal background in contrastive explanations, see Marchionni 2006). Whether an
assumption is duly or unduly unrealistic depends on its location in a theoretical
structure and the functions it is designed or able to serve.