Abstract
In light of Laura Sizer's and Robert Thayer's models of mood, I propose a functional theory to explain in what sense moods are adaptive. I argue that mood involves a mechanism which monitors our physical and mental energy levels in relation to the perceived energy demands of our environment, and generates corresponding cognitive biases in our reasoning style, attention, memory, thought, and creativity. The function of this mechanism is to engage us in the right task with the right amount of energy by maintaining equilibrium between the energy we possess and the energy our environment demands