For psychologists, desires arise from bodily structures and functions (e.g., the stomach needing food and the blood needing oxygen). On the other hand, emotions arise from a person's mental state.

How is desire created?

In general, desire begins in a relatively automatic manner as the brain pleasure centers evaluate external incentives against the state of mind (e.g., hungry, craving, or feeling lonely). For example, negative mood can be a cue that triggers desires to improve one's current state.

What is the source of desire?

Mill suggests that a desire for an object is caused by an idea of the possible pleasure that would result from the attainment of the object. The desire is fulfilled when this pleasure is achieved. On this view, the pleasure is the sole motivating factor of the desire.