We encounter the word “world” often in philosophy, particularly in the phrases “possible worlds” and “the actual world” but also in the unmodified “the world”. We also speak in philosophy of “the physical world” or “the biological world” or “the world of science”. What does the word “world” mean in these locutions? Does it mean the same thing in both uses? It trips off the tongue easily enough, but it is seldom scrutinized. How does it relate to the ordinary meaning of “world”? What is that ordinary meaning? The OED gives us some clues: “the earth with all its countries and peoples”; “a region or group of countries: the English-speaking world”; “all that belongs to a particular historical period or sphere of activity: the world of British theatre”; “another planet like the earth”. It is clear from these definitions that “world” is used in a more limited sense in ordinary speech than it is in philosophy. Wittgenstein’s use in “The world is all that is the case” and “The world is the totality of facts, not of things” suggests a much broader notion of world than the ordinary use (akin to Leibniz’s notion). The word “world” is a count noun connoting a natural kind with appropriate criteria of identity attached. It can mean roughly the same as “planet” or it can mean a specific type of activity or occupation—“the world of physics”, “the fashion world”, “welcome to my world”, and so on. Thus, the criteria of identity will pertain to what makes one planet different from another or what makes one sphere of activity different from another. Clearly, there are many planets and many spheres of activity. When we speak of “the physical world” we speak in this restricted way: we mean something like “the world consisting of physical entities and physical laws”—in contrast to “the mental world” or “the abstract world”. Popper spoke of the “three worlds” theory in this sense. Star Trek spoke of “exploring new worlds”. H.G. Wells wrote about “the war of the worlds”. These are all legitimate uses clearly tied to the ordinary dictionary definition: we know what kind of thing we are referring to and how to count instances of the kind. But the philosophical use is different, or purports to be. As Wittgenstein uses the word, a world is a set of facts that includes all those that actually obtain. He doesn’t mean anything like “The physical world is the totality of physical facts”; he means facts of all kinds, however heterogeneous. He is doing exactly what he excoriates in the Investigations: taking a word from ordinary language with a clear meaning and re-deploying it to mean something that belongs only to philosophy. The word retains its old associations in the new context while being tacitly stipulative (and misleading). What it appears to mean in the new context is simply a set of facts united by nothing except that they are facts; they are not facts limited to a specific type (e.g., facts concerning the British theatre). But this is not a world in the ordinary sense, so it is really not a world at all; it is just an arbitrary collection. It is like saying “A species is a totality of animals”: granted a species is made up of a totality of animals, but it is not the case that any totality of animals is a species. That is just a misuse of the word “species” (a set consisting of a mouse, a monkey, and a mongoose is not a species). Similarly, a set of unrelated facts is not a world but merely an arbitrary collection. True, there are such collections (though they tend not to have much interest), but it is a misuse of language to characterize them as “worlds”. By using this word, we lay claim to a kind of unity that doesn’t exist in the totality in question (still less in a planet like the earth). To put it more bluntly, there is no such thing as the world, only various worlds restricted in the ways described. This is a philosopher’s fiction designed to seem like a conceptual advance or substantive theory. When we speak of “the world” in this alleged sense we speak of nothing—unless we admit we are using the word metaphorically (in which case our metaphor is a bad one). So, the phrase “the actual world” has no meaning; it denotes nothing. Likewise, there are no “possible worlds”, since that phrase also stretches the word “world” beyond its regular sense. These phrases contrive to give the impression that they have a familiar and intuitive meaning (the ordinary meaning) but in fact they do not. Translated into literally correct language, they must mean something like “the total set of actual facts” and “suitably large sets of possible facts”. These locutions, awkward and unintuitive as they are, cannot be glossed in the language of “worlds” that we are familiar with. Not to put too fine a point on it, this would be simply cheating—using words with a certain established meaning but in a way that can’t sustain that meaning. So, the idea of “possible worlds semantics” is chimerical, ill-defined, and incoherent. It’s like trying to do zoology by using the word “species” but meaning by it “any old collection of animals”. And notice how heterogeneous the facts have to be in so-called possible worlds semantics: physical and mental, mathematical and moral, fictional and factual, necessary and contingent, etc. In no sense do these facts form a totality deserving to be called a “world”. They are really many worlds bundled into one—the bundle theory of possible worlds (but a mere bundle can never be a genuine world). There are therefore no possible worlds to quantify over, to compare with one another, to act as arguments of functions, to be places in which objects of reference exist, to be truth conditions of counterfactuals, etc. We can keep the formal apparatus if we like, but we are not entitled to describe it in the ways to which we have become accustomed. That is simply false advertising, verbal sleight of hand, conceptual cheating. The very idea of a unified whole consisting of the set of all true propositions (actual facts) starts to seem spurious, a verbal illusion sustained by an overly extended use of the ordinary word “world”. To be sure, there are many worlds in the ordinary sense, but there is no single big world to which they all belong (“the world”); that is a piece of philosophical fiction. Worse, it is a type of nonsense.
 These definitions are drawn from the Concise Oxford English Dictionary; there is a much longer set of definitions in The Shorter Oxford English Dictionary in which no reference is made to the standard meaning in contemporary analytical philosophy. Emphasis is laid on worlds as relating to human life and the world as the material universe.
 Here we see the power of custom or convention: we have become so used to speaking of possible worlds and the actual world that we can’t see how distorting and artificial such usage is. We have to step back from our linguistic practices as philosophers in order to see how mangled our speech has become. In our professional world it has become de rigueur to misuse the word “world”. I have a book before me called Concise Atlas of the World: that is how to use the word “world”. There is no atlas covering Wittgenstein’s “the world”, or David Lewis’s, or even Saul Kripke’s—because there is no such natural entity. What is called a “possible world” is an artificial human construction not deserving of the label.