Modes of experience correspond to groups of nets that are commonly used together. The principle modes of Experience are observation, imagination and sensation. Imagining is popularly known as "mental activity". It includes inner speech and all other types of imagining. However, all of Experience is mental activity and the difference between sensation and inner speech/imagining is that the first deals with events that have their sources in the world beyond the brain and the latter is mostly sourced from within the brain.