Models may be very simple or very complex. Since the world we observe cannot be observed in totality, each model reflects only a limited aspect of the total world. No single model, or combination of models, reveals the truth of the structure of reality. Each model reveals and orders reality from a particular perspective.
Learning theory is the study of how people learn. Instructional Design Theory is the study of how to best design instruction so that learning will take place. Instructional design theory, then, is drawn from learning theory.