 Postmodernists claim that what we think of as reality is “discursively constructed.” According to Saussure, “the linguistic sign acts reflexively, not referentially” in a “discursive field.” This amounts to radical holism about meaning: signs get their meaning not from their reference to external things but from their relations to all the other signs in the discourse. Introducing new signs (or discarding old ones) thus changes the meanings of the signs already in use. Signs therefore lack a fixed meaning over time. These ideas support the rejection of what Lyotard calls “totalizing metanarratives.” There can be no complete, unified theory of the world that captures the whole truth. A discourse with different terms would contain meanings not available in the discursive field of the theory that claims completeness. The assertion of any particular theory is an exercise of “power”—to exclude certain possibilities from thought and authorize others. Postmodernist claims that objects are “discursively constructed” or “socially constructed” assert a kind of nominalism: that the world does not dictate the categories we use to describe it, that innumerable incompatible ways of classifying the world are available to us. The selection of any one theory is a choice that cannot be justified by appeal to “objective” truth or reality.