This chapter presents the physicalist–objective (PO) model of human action taken together with identity theory. Implicit in the PO account of agent action is the view that the unity of personality depends on a unified pattern of integrated central systems. However, far from disregarding such a puzzling and counter-intuitive consequence of the primitive agent-action model, what is clearly indicated here is a radical incoherence in the orthodox account of action and the need for a thorough re-examination of the basic agency model that involves such consequences. The outstanding feature of human behaviour, that which has most consistently been held to set human action apart from purely physical and causally determined processes, is its goal-directedness. Goal-directedness, therefore, does not set human behaviour apart from the category of physical causation. A consideration of one of the best-known and simplest goal-directed feedback-regulated systems, the thermostatic control, will quickly establish this.