Philip K. Dick wrote that “the paranoid is totally rigid”, but there is an element of flexibility to the systems that paranoid people construct that is critical to the systems’ ability to endure. The more that a belief is rigidly universalizing – “all sheep are white” – the stronger the possibility that we encounter evidence that would force us to revise it. If we see a sheep that is not white, then the belief that all sheep are white will wither. The types of beliefs that are central to paranoia, by contrast, are vague in the sense that there is no clear way of falsifying them, and this gives them a flexibility that enables one to adduce more-or-less any stimulation as positive evidence of their truth.
Things get more complicated, of course, once we start thinking about language. We do not simply encounter a sheep that is not white; we encounter something that meets our definition of sheep that is not white. One might say that we have two options when faced with the evidence – we can either revise our belief that all sheep are white, or else we can revise our definition of sheep. If we accept, as I do, Quine’s thesis that there is no “fact of the matter” about analyticity of sentences, then there is actually no clear difference between these two responses. Is our belief that all sheep are white a part of our mental definition of “sheep,” or is it information we have gleaned from experience about a concept that is defined by other characteristics? The answer is that this is not a well-formed question, at least empirically speaking. Every belief we have about sheep contributes, if only in some small way, to what the word means to us; it is only that some of these beliefs are closer to the surface, where the empirical force can more easily affect them, than others.
Thought in these terms, paranoia is a state in which the deep mental connections to a proposition at the center of one’s worldview are too few, or too weak, to avoid being easily altered by new evidence. The difference between believing that “all sheep are white” and believing that “the toaster is out to get me” is that there is not adequate mental rigging fixing the meaning of “out to get me” in that context, while presumably there is for the word “sheep.” Because of this lack of fixity, observational evidence no longer serves to improve the paranoid’s beliefs by forcing revision of them. Instead, it pulls their existing beliefs this way and that.