Our ethical obligations to another being depend at least in part on that being's capacity for a mental life. Our usual approach to inferring the mental state of another is to reason by analogy: If another being behaves as I do in a circumstance that engenders a certain mental state in me, I conclude that it has engendered the same mental state in him or her. Unfortunately, as philosophers have long noted, this analogy is fallible because behavior and mental states are only contingently related. If the other person is acting, for example, we could draw the wrong conclusion about his or her mental state. In this article I consider another type of analogy that can be drawn between oneself and another to infer the mental state of the other, substituting brain activity for behavior. According to most current views of the mind–body problem, mental states and brain states are non-contingently related, and hence inferences drawn with the new analogy are not susceptible to the alternative interpretations that plague the behavioral analogy. The implications of this approach are explored in two cases for which behavior is particularly unhelpful as a guide to mental status: severely brain–damaged patients who are incapable of intentional communicative behavior, and nonhuman animals whose behavioral repertoires are different from ours and who lack language.