Here are three potential models for mood. They depend on whether good and bad moods are the opposite sides of a continuum, if one is simply the absence of the other, or if they are two separate generative systems:
1) Mood is dualistic and generative. There is one system for good moods and a second system for bad moods.
2) Mood is a single generative system; it naturally generates a good mood until there is a problem and this system malfunctions or is under-activated; only then do people go into bad moods (conversely people are naturally in a bad mood until that single system malfunctions and people have good moods).
3) Mood is not an efferent system in relation to the individual at all. Instead the individual is receptive to moods from outside. A person contemplates or reflects moods received externally. Negative moods would be explained by either receiving negative moods, or by neglect- not receiving positive moods (again 1 or 2 above, but from an external source). Either way, there is no internal system that bears majority of responsibility for generating mood.
