This is the first post of what should become a series of posts on randomly chosen classic texts in the philosophy of information.
In “Epistemology without a Knowing Subject” Karl Popper introduces the Third World of objective contents of thought and contrasts this with the first world of physical objects and / or physical states, and the second world of mental states. This is also the paper where he famously coined the term objective knowledge which had an influence on both information-science and the philosophy of information. An excerpt:
An objectivist epistemology which studies the third world [the objective content of thoughts] can help to throw an immense amount of light upon the second world of subjective consciousness, (. . . ); but the converse is not true. (p. 338)
Reference: K.R. Popper, “Epistemology without a Knowing Subject”, Logic, Methodology and Philosophy of Science III , B. Van Rotselaar and J.F. Staal, ed., Amsterdam: Noth-Holland, 1968, p. 333-373.