World 1: The physical world, the world of physical objects and events, including biological entities.
World 2: Subjective reality, the world of mental objects and events, that occur in (individual) minds.
World 3: Objective knowledge, the world of all products of thought, that may be physical or not.
Instead of physical or mental monism, or the dualism of mind and matter, Popper suggested a pluralism (triplism?) consisting of three worlds. All the elements of each of these worlds, Popper argued, can be said to exist.
One could say that each higher world requires the world below it in order to exist: World 1 < World 2 < World 3. That is, World 2 is emergent or supervenient on World 1, and World 3 is emergent or supervenient on World 2. In addition, these worlds interact with each other.
There is no necessary evaluation of the “truth” of the elements of World 3. There are many products of thought that exist in World 3 that are indeed false. But Popper spends much time talking about the quality of World 3 objects that give credence to their existence. That is, the “objective” goodness or quality of a product makes that product more real.
I suggest that the introduction of another world is necessary for a proper division and understanding of Popper’s Three Worlds. Let’s call it
World 4: Normative values, the world of all intersubjective evaluations.
Indeed, Popper argues that the objective value of certain objects in World 3 gives credibility to the notion that there are such World 3 objects, and not just World 2 instances within minds.
World 4 could serve as a mediator between World 2 and World 3. Popper states that people can evaluate the World 3 products of the mind within their own subjectivities, but it seems to me that they must be trained or lead to appreciate the “objective” greatness of these products. They do not happen in a vacuum, so perhaps a better description would be that they have an “intersubjective” value.
Why would a person discount the well accepted scientific theories of evolution or climate change just because they don’t fit with his other beliefs?
Why would a person destroy ancient sculptures of timeless beauty just because it offends his religious beliefs?
Such cognitive biases could easily block a person from accepting some objective knowledge that conflicts with their values. Certainly the biases exist in the subjective mind, but are learned and maintained in the intersubjective cultural milieu.
A takeaway fourfold for you is presented on the right.
Karl Popper / Three Worlds. The Tanner Lecture on Human Values, delivered at the University of Michigan, 1978
Sean Carrol / The Big Picture: On the Origins of Life, Meaning, and the Universe Itself
Manfred Eigen, Ruthild Winkler / Laws of the Game: how the principles of nature govern chance