In contrast to objective materialism, subjective idealism is the simple assumption that the mind and free choice are actually what determines the illusion of objective materialism. Idealism supposes that the subjective free choice of the mind that sees its own retina and that free choice determines the illusion of objective matter changes as a retina. Subjective idealism further argues that objective materialism is an illusion of the mind and that the subjective actions of the mind determine the only true reality. Even though the mind and free choice are made up of the action potentials of neural matter, idealism somehow still assumes that there is no objective materialism outside of the subjective mind.
Free choice is a mystery of the mind and is how minds affect matter action and while there are many different definitions of consciousness, in contrast, free choice has a simple definition. Free choice is how we make the world more desirable given a feeling that we have about a choice. Since we only perceive the objective world of retinas with the subjective mind's retina, the mystery is whether objective materialism of retinas exists outside of subjective free choice of the mind's retina or whether subjective free choice of the mind's retina is how objective materialism of retinas seems to exist.
We use knowledge of the world of objective materialism of retinas to predict likely outcomes from precursors, like seeing a retina with a retina, but knowledge has no meaning without free choice. There is a free choice of the mind's retina to see an objective retina, but without knowledge of retinas and mirrors, the image would have no meaning. The very meaning of free choice is tied to a lifetime of knowledge and experience.
Very simple organisms have likewise very simple neural networks that nevertheless also provide free choice to those organisms. The neural networks of the hydra or nematode both freely choose outcomes that depend on precursors, but those free choice outcomes are never completely predictable or determinate from those precursors. Classically, it is the chaos of random noise that limits the precision of predictions and there is no limit to the possible precision of a prediction. However, there are quantum limits to the precise prediction of all action in the universe is subject to a well-defined and discrete quantum limit.
Objective materialism predicts most likely outcomes from matter, action, and quantum phase given a set of precursors along with some random chaos. Since we can share those predictions with others, these predictions are the objective reality of materialism despite the random chaos. However, materialism still means free choice based on a set of precursors that determine feeling and so those objective materialist choices are still part of the same subjective reality of idealism.
Subjective idealism also chooses an outcome based on a set of precursors that determine feeling and that feeling is not possible to completely know. Since we choose based on feelings and feelings are unique for each person, free choice forms a subjective reality that is unique for each person. Feeling is a neural action that derives from the action of a moment of thought, a lifetime of precursor memories, and sensations of the moment. Even though we can share measurements of matter action with others, idealism still supposes that objective reality is just an illusion of our subjective reality.