In metaphysics, the philosophical branch that deals with questions pertaining to the nature of reality, there is the term some times used called “metaphysical zombie,” (MZ) coined by professor David Chalmers. The term is especially helpful in the philosophy of mind (a big field in metaphysics) in which questions pertaining to the likes of mental states and consciousness are studied. What the MZ focuses on is the existence of minds and consciousness in human beings and other animals, and I believe the concept to be a helpful analogy for unpacking the limitations of our knowledge.
Most of us assume that other human beings and animals are conscious creatures with minds of their own. By consciousness I mean a person or animal’s mental states (thoughts, emotions, desires), the ability to perceive these states within oneself (introspection), as well as perceive the world (extrospection). But for many of us it seems that animals and humans are conscious creatures is just downright obvious, “Obviously other people have minds like my own! Duh.” But this belief is much less obvious than one might initially think.
Why? Well, because ultimately we have no way to verify that other human beings have minds and conscious experiences except through the process of extrapolation from our own subjective conscious experiences to them. Rather, we simply suppose that other human beings have this thing we call consciousness and conscious experience because we believe that they behave and interact in the world in similar ways to us. But as some philosophers have pointed out, this kind of knowledge can be challenged. One challenge is that sometimes our experiences of the world are mistaken and that our cognitive faculties are fallible. But if we grant its fallibility in some sense it is conceivable that it could be fallible in many, if not most cases. I am not saying it is, rather I am saying that it is conceivably true. Now, if we grant this then it could include our belief that human beings are conscious creatures that possess minds of their own.
Another challenge to the extrapolation from our own experiences to support the notion of consciousness in other human beings is in the subjectivity of conscious experience. Philosopher Thomas Nagel argued this point in his essay, What Is It Like To Be A Bat?, that even if neuroscience could fully map out the physical brain of an animal one would still be unable to know what it would feel like to be the animal. In other words, there is a subjectivity to an animal’s conscious experience that cannot be discovered through the sciences. After all, a neuroscientist could examine which part of the brain lights up when I am thinking about a specific thing but he could never know the contents of my thought. This fact brings forth significant questions: if consciousness is a subjective experience then how can we know that it exists in other people? And, moreover, how can we know that their experience of consciousness is the same in other human beings and animals as it is in us? I think these questions strongly show the limitations in our knowledge on the question.
So, if one were to run to extremes with the MZ concept then it is possible to argue that the only mind that exists is one’s own, and that what she perceives to exist in other human beings, namely that they have minds and conscious experiences, is an entirely false view of reality. After all, on the MZ concept these apparent human beings could be entities indistinguishable from ordinary human beings in that they look like humans, act like humans, and respond like humans but entirely lack conscious experience. In fact, there would be no way that I could show that this isn’t the case.
But I don’t believe this to be true to reality for the simple reason that I believe that other human beings possess minds and consciousness of their own. Rather, I have to admit the limits of my knowledge and that I could fully be wrong in these views. Thus, I hold that I am rational to believe that other human beings are conscious creatures that have minds until some logical defeater undermines my view. And ultimately I think that that’s as far as one could justify this view.