Karl Popper’s theory of World 3 (from Popper, by Bryan Magee, London 1973)

Throughout his account of the evolution of life and the emergence of man and the development of civilization, Popper makes use of the notion not only of an objective world of material things (which he calls World 1) and a subjective world of minds (World 2) but of a third world, a world of objective structures which are the products, not necessarily intentional, of minds or living creatures; but which, once produced, exist independently from them. Forerunners of this in the animal world are nests built by birds or ants or wasps, honeycombs, spiders’ webs, beavers’ dams, all of which are highly complicated structures built by the animal outside of its own body in order to solve its problems. The structures themselves become the most centrally important part of the animal’s environment, towards which much of its most important behaviour is oriented – indeed, it is commonly born in one of them, which in that case constitutes its very first experience of the physical environmenmt outside its mother’s body. Furthermore, some of the animal kingdom’s structures are abstract: forms of social organization, for instance, and patterns of communication. In man, some of the biological characteristics which developed to cope with the environment changed that environment in the most spectacular ways: the human hand is one example. And man’s abstract structures have at all times equalled in scale and degree of elaboration his transformation of the physical environment: language, ethics, law, religion, philosophy, the sciences, the arts, institutions. Like those of animals, only more so, his creations acquired a central importance in the environment to which he had then to adapt himself, and which therefore changed him. Their objective existence in relation to him meant that he could examine them, evaluate and criticize them, explore, extend, revise or revolutionize them, and indeed make wholly unexpected discoveries within them. And this is true of his most abstract creations of all, for example mathematics. “I agree with Brouwer that the sequence of natural numbers is a human construction. But although we create this sequence, it creates its own autonomous problems in its turn. The distinction between odd and even numbers is not created by us: it is an untintended and unavoidable consequence of our creation. Prime numbers, of course, are similarly unintended autonomous and objective facts; and in their case it is obvious that there are many facts here for us to discover: there are conjectures like Goldbach’s. And these conjectures, though they refer indirectly to objects of our creation, refer directly to problems and facts which have somehow emerged from our creation and which we cannot control or influence: they are hard facts, and the truth about them is often hard to discover. This exemplifies what I mean when I say that the third world is largely autonomous, though created by us.” World 3, then is the world of ideas, art, science, language, ethics, institutions – the whole cultural heritage, in short – in so far as this is encoded and preserved in such World 1 objects as brains, books, machines, films, computers, pictures, and records of every kind.