The ancient Greeks had a fantastical but enlightening way of looking at this. As they saw it, when a person got angry, he was possessed by the spirit of anger. When he had a good idea, it did not come from his own mind, but was rather whispered to him by a muse. Although this explanation might seem supernatural, it is in some ways true to our experience. When anger comes, it doesn't seem to come from us. It wells up from some other source. It washes over our consciousness and briefly we are drowned. Similarly, when inspiration touches us, it happens all so instantaneously that it's like someone is telling us something, rather than that we have contrived these ideas on our own.
Ancient Christians had a similar view of human nature. That is, human nature was minimal. Instead, demons and angles were constantly guiding our actions. When we walked by something valuable and beautiful, the demon of envy whispered in our ears that we should take it. This thought was not our own, but rather borne from some external presence. Once again, this is true to our experience. Temptation seems to come from something other than our typical consciousness. What the ancient Christians called demons and angles, though, I would call discreet elements of the psyche. Just as there is a right brain and a left brain, an imagination and a verbal consciousness, there is a lust, a sloth, a pride, a love, a fear, a faith, an inspiration. They are all a part of us, and yet when they interact with our dominant consciousness, they are alien.
These days, psychologists are coming to refer to the mind not as a discreet psychic entity, but more like a boardroom. It is the chatter of several dozen impulses and outlooks, and only after conflict and compromise does it come to a conclusion. At the same time, certain elements dominate certain people. Some people are dominated by their imaginations. Some by their logic. Some, by lust; others, by pride. What dominates you?