During my summer vacation, my brother and I were walking along the beach and I asked him, “So, what do you think is the nature of reality?” Although my brother is a financial planner, he also is quite reflective and philosophical. “Well,” he said, “I would start with the fact that there is the world out there and then there is my conscious experience of it, which works like a mirror of nature, the external world.”

That launched us on a discussion that would be one of the more fruitful ones I had with my family over the break. I replied that I was reading up on an interesting formulation of human reality by the famous philosopher of science, Karl Popper.

Popper posited the existence of three worlds, which he described as follows:

To sum up, we arrive at the following picture of the universe. There is the physical universe, World 1, with its most important sub-universe, that of the living organisms. World 2, the world of conscious experience, emerges as an evolutionary product from the world of organisms. World 3, the world of products from the human mind, emerges as a product from World 2. In each of these cases, the emerging product has a tremendous feedback effect upon the world from which it emerged.

I told my brother that his “world out there” corresponded to Popper’s World 1. His conscious experience of the sun, waves and sand corresponded to Popper’s World 2. Finally, our talking about these worlds and generating an objective language-based description of them was Popper’s World 3.

I also shared with him that Popper's formulation corresponded quite well to my Tree of Knowledge System. Popper’s World 1 corresponds to the dimensions of Matter and Life, World 2 corresponds to Mind and World 3 corresponds to Culture.


My brother readily agreed that the world of explicit language-based beliefs could be fruitfully added to his intuitive conception. We spent much of the next several days talking about understanding reality from these three worlds. It was very encouraging to me how easy it was for us to identify clear examples of entities that were in one world or the other, as well as discussing interfaces between the worlds. So next time you are reflecting on how you make sense out of reality, it might be helpful to start with dividing it up into these three worlds.

Finally, these three worlds are useful in describing the key naturalistic domains, but they also might be useful in discussions with those operating from a supernatural frame. The supernatural, if it exists, would represent a fourth world. 

Karl Popper

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