Adequation

According to Aquinas, truth is the adequation of a thing to the intellect. Equivalently, truthful understanding amounts to having an adequate mental model of the part of reality which one has understood.

In terms of software development, a good object model is characterised by a high degree of adequation between objects in the problem domain (the "things" in reality) and software objects (the models used by the computational intellect).

Good object models need to be able to describe all valid states of the problem domain while creating as little opportunity for representing invalid states. Good behavioural models need to restrict state transitions to the valid ones and rule out state transitions that are not possible in reality.