One of the more popular epistemology models (except for perhaps in the training/learning/behavioral sciences) is Sir Karl Popper's writings on the Three Worlds of Knowledge. The behavioral sciences (knowledge/learning/management professions) seem to prefer and stay within the realm of Michael Polanyi's concept of tacit and explicit knowledge. However, Polanyi's epistemology is narrower and has a limited basis for understanding knowledge as compared to Popper's work, which provides a broader epistemological foundation.
World 1 The physical universe
It consists of the actual truth and reality that we try to represent, such as energy, physics, and chemistry. While we exist in this world, we do not always perceive it and then represent it correctly.
World 2 Our subjective personal perceptions
World 2 is our subjective personal perceptions, experiences, and cognition. It is what we think about the world as we try to map, represent, and anticipate or hypothesis in order to maintain our existence in an every changing place. Personal knowledge and memory form this world, which are based on self-regulation, cognition, consciousness, dispositions, and processes. Note that Polanyi's theory of tacit and explicit knowledge is based entirely within this world.
World 3 Sum of Objective Products of the Mind
World 3 is the sum total of the objective abstract products of the human mind. It consists of such artifacts as books, tools, theories, models, libraries, computers, and networks. It is quite a diverse mixture. While knowledge may be created and produced by World 2 activities, its artifacts are stored in World 3.
Example: a claw-hammer, Maslow's hierarchy of needs, and Godel's proof of the incompleteness of arithmetic. Popper also includes genetic heredity (if you think about it, genes are really nothing more than a biological artifact of instructions).
Relationship Between Worlds
And of course, there are various relationships between these three worlds:
World 1 drives and enables world 2 to exist, while world 2 tries to control and regulate world 1.
World 2 produces world 3, while world 3 helps in the recall and the training/education/development/learning of world 2.
World 3 describes and predicts world 1, while world 1 is the inferred logic of world 3.
In addition, since world 2 is composed of people, we can use our senses to cut across boundaries and observe and test the exchanges and relationships of worlds 1 and 2. Thus, knowledge surrounds us (world 1), becomes a part of us (world 2), and is then stored in historical contents and contexts by us (world 3 artifacts).
In this framework are two different senses of knowledge or thought:
Knowledge in the subjective sense, consisting of a state of mind with a disposition to behave or to react [cognition].
Knowledge in an objective sense, consisting of the expression of problems, theories, and arguments.
While the first is personal, the second is totally independent of anybody's claim to know — it is knowledge without a knowing subject.