https://en.wikipedia.org/wiki/Popper%27s_three_worlds
The three worlds may be understood, in this evolutionary and cosmological sense, as containing three categories of entity:
- World 1: the realm of states and processes as studied by the natural sciences. These include the states and processes that we seek to explain by physics and by chemistry, and also those states and processes that subsequently emerge with life and which we seek to explain by biology.
- World 2: the realm of mental states and processes. These include sensations and thoughts, and include both conscious and unconscious mental states and processes. World 2 includes all animal as well as human mental experience. These mental states and processes only emerge as a product of biological activity by living organisms, and so only emerge subsequent to the emergence of living organisms within World 1.
- World 3: the realm of the 'products of thought' when considered as objects in their own right. These products emerge from human "World 2" activity, but when considered as World 3 objects in their own right they have rebound effects on human World 2 thought processes. Through these rebound effects, World 3 'objects' may - via World 2-based human action on World 1 - have an indirect but powerful effect on World 1. In Popper's view, World 3 'objects' encompass a very wide range of entities, from scientific theories to works of art, from laws to institutions.
