Abstract
This speech discusses the processes of reasoning that are entailed in the building of scientific models and sets forth some generally accepted principles of model building. The speaker emphasizes that a “good” model can only be defined in terms of its usefulness, which in turn can only be judged against the intended use of the model. A model can never be said to be “correct” or “incorrect.” In light of these principles, the speaker suggests a critique of various different versions of the ego state model.