LLMs Lack a Theory of Mind and So Can’t Perform Speech Acts—A Causal Argument

Abstract

I advance a causal argument for the conclusion that large language models (LLMs) lack Theory of Mind and so can’t perform speech acts. The argument is causal in that the animating idea is that LLMs are unable to learn or understand causal relations, a claim that I support by drawing on the views of Judea Pearl. I argue that if LLMs have this sort of causal problem, it follows that they cannot possess Theory of Mind, given the further premise that Theory of Mind should be understood as a causal theory. I then argue that if LLMs lack Theory of Mind, they cannot perform speech acts, given the further premise that speech acts require reflexive-communicative intentions and so require Theory of Mind. As a consequence of the result that LLMs cannot perform speech acts, I conclude that their utterances lack speaker meaning. After setting out this argument, I consider an objection to my view based on the observation that LLMs perform fairly well on Theory of Mind benchmarks. I reply to this objection by proposing that LLMs rely on a different type of mechanism than human beings do to achieve this performance; I support this proposal by pointing to a form of behavior that LLMs do not exhibit but that we should expect them to exhibit if they possessed Theory of Mind.