Ideas, according to Berkeley, can only exist in one or another mind that is capable of perceiving them. The two types of ideas known to human beings are ideas of sense, which come into the mind from somewhere outside it, and ideas of the imagination. God, however, who creates all ideas out of nothing, does not have ideas of sense because nothing can affect Him. God has only ideas of imagination.

No idea is capable of doing anything on its own; every idea is passive. Only minds can act or do anything. All ideas must exist in minds. Without minds, there are no ideas.