The mental world is an ontological category in metaphysics, populated by nonmaterial mental objects, without physical extension (though possibly with mental extension as in a visual field, or possibly not, as in an olfactory field) contrasted with the physical world of space and time populated with physical objects, or Plato's world of ideals populated, in part, with mathematical objects.
Descartes argued for a mental world as separate from the physical world. Debates regarding free will include how it could be possible for anything in the mental world to have an effect on the physical world. In various forms of Epiphenomenalism, the physical world can cause effects in the mental world, but not conversely. Behaviorists deny that a mental world can be meaningfully referred to.
- Synopsis of Consciousness and Berkeley's Metaphysics. ... "What are the basic constituents of the mental world?", Consciousness and Berkley's Metaphysics, Peter B. Lloyd, 2008
- Gottlob Frege, Foundations of Arithmetic
- Metaphysics, Richard Taylor, Foundations of Philosophy series
- Problems of Philosophy, Bertrand Russell
- History of Western Philosophy, Bertrand Russell
- Meditations, Renes Descartes
- Beyond Freedom and Dignity, B. F. Skinner