LAUSR

: Do minds have immune systems? In this paper, we remove several obstacles to deciding this question in a rigorously scienti�ic way. First, we show why the scienti�ic community needs to take up the question. Then, we give the hypothesis a name: the Mental Immune Systems Thesis (or MIST) is the claim that minds do in fact have immune systems. It’s tempting to dismiss this claim as “mere metaphor” – and many do – but that stance turns out to be indefensible. It is at best a well-intentioned stopgap: one that postpones a pivotal reckoning. So how to settle the question? Above all, we need clarity about the meaning of “immune system.” To that end, we examine candidate de�initions, nominate one, and show why it makes sense to embrace that de�inition. We then consider an evolutionary argument for MIST: mental immune systems, so de�ined, didn’t just evolve, they had to evolve – to protect minded creatures from informational threats. We then detail some of MIST’s testable implications and summarize the extant empirical evidence. Finally, we discuss the prospects of cognitive immunology , a research program that (1) posits mental immune systems and (2) proceeds to examine and explain how they work. MIST, we conclude, is a hypothesis that deserves serious scienti�ic development.