Monistic Idealism is a metaphysical theory which states that consciousness, not matter, is the ground of all being. It is a monistic theory because it holds that there is only one type of thing in the universe, and it is a form of idealism because it holds that one thing to be consciousness. In India this concept is central to Vedanta philosophy.
It rejects any notion of consciousness being an accident or the mere side product of material interactions. Instead, consciousness comes before matter. Monistic idealism is the fundamental wellspring from which reality is created.
It is theorized that everything is made of matter, and everything can be reduced to the elementary particles of matter, the basic constituents or building blocks of matter. Cause arises from the interactions of these basic building blocks or elementary particles. Elementary particles make atoms, atoms make molecules, molecules make cells, and cells make the brain. But through all of this, the ultimate cause is always the interactions between the elementary particles.
The belief is that all cause moves from the elementary particles and is called upward causation. In this view, what human beings think of as our free will does not really exist. It is only a secondary phenomenon, secondary to the causal power of matter. Any causal power that we seem to be able to exert on matter is simply an illusion. This is the current view of reality.
The opposite view is that everything starts with consciousness and is the ground of all being. In this view, consciousness imposes downward causation. In other words, our free will is real. When we act in the world we really are acting with causal power. This view does not deny that matter also has causal potency and that there is causal power from elementary particles upward. It insists that there is also downward causation. It shows up in our creativity and acts of free will, or when we make moral decisions. In those occasions we are actually witnessing downward causation by consciousness.