Models and Theories:

"As a scientist I make a sharp distinction between models and theories. A theory is a construction, built out of logic and mathematics, that is supposed to describe the actual universe that we live in. A model is a construction that describes a much simpler universe, including some features of the actual universe and neglecting others. Theories and models are both useful tools for understanding nature. They are useful in different ways, and it is important to keep the difference in mind. A theory is useful because it can be tested by comparing its predictions with observations of the real world. On the other hand, a theory may be useless because its consequences are too complicated to be predicted. A model is useful because its behavior is simple enough to be predicted and understood. On the other hand, a model may be useless because it leaves out too much and looses any connection with reality. As we explore the universe, we move out from well-trodden ground into the unknown. On well-trodden ground we build theories. On the half explored-frontiers we build models."

Freeman Dyson