Nagel, Thomas, "What is it like to be a bat?" [abridged - 2000 words ] From The Philosophical Review LXXXIII, 4 (October 1974): 435-50.
Consciousness is what makes the mind-body problem really intractable. We have at present no conception of what an explanation of the physical nature of a mental phenomenon would be. Most reductionist theories do not even try to explain it. Conscious experience is a widespread phenomenon. It occurs at many levels of animal life, though we cannot be sure of its presence in the simpler organisms, and it is very difficult to say in general what provides evidence of it.
No doubt it occurs in countless forms totally unimaginable to us, on other planets in other solar systems throughout the universe. But no matter how the form may vary, the fact that an organism has conscious experience at all means, basically, that there is something it is like to be that organism.
Fundamentally
an organism has conscious mental states if and only if there is
something that it is to be that organism. We may call this
the subjective character of experience.
To illustrate the connection between subjectivity and a point of
view, and to make evident the importance of subjective features,
it will help to explore the matter in relation to an example that
brings out clearly the divergence between the two types of conception,
subjective and objective.
I assume we all believe that bats have experience. Bats nevertheless present a range of activity and a sensory apparatus so different from ours that the problem I want to pose is exceptionally vivid (though it certainly could be raised with other species). Even without the benefit of philosophical reflection, anyone who has spent some time in an enclosed space with an excited bat knows what it is to encounter a fundamentally alien form of life.
I have said that the essence of the belief that bats have experience is that there is something that it is like to be a bat. Now we know that most bats perceive the external world primarily by sonar, or echolocation, detecting the reflections, from objects within range, of their own rapid, subtly modulated, high-frequency shrieks. Their brains are designed to correlate the outgoing impulses with the subsequent echoes, and the information thus acquired enables bats to make precise discriminations of distance, size, shape, motion, and texture comparable to those we make by vision. But bat sonar, though clearly a form of perception, is not similar in its operation to any sense that we possess, and there is no reason to suppose that it is subjectively like anything we can experience or imagine. This appears to create difficulties for the notion of what it is like to be a bat. We must consider whether any method will permit us to extrapolate to the inner life of the bat from our own case, and if not, what alternative methods there may be for understanding the notion.
Our own experience provides the basic material for our imagination, whose range is therefore limited. It will not help to try to imagine that one has webbing on one's arms, which enables one to fly around at dusk and dawn catching insects in one's mouth; that one has very poor vision, and perceives the surrounding world by a system of reflected high-frequency sound signals; and that one spends the day hanging upside down by one's feet in an attic. In so far as I can imagine this (which is not very far), it tells me only what it would be like for me to behave as a bat behaves. But that is not the question. I want to know what it is like for a bat to be a bat. Yet if I try to imagine this, I am restricted to the resources of my own mind, and those resources are inadequate to the task.
The
problem is not confined to exotic cases, however, for it exists
between one person and another. The subjective character of the
experience of a person deaf and blind from birth is not accessible
to me, for example, nor presumably is mine to him. This does not
prevent us each from believing that the other's experience has such
a subjective character.
The fact that we cannot expect ever to accommodate in our language
a detailed description of Martian or bat phenomenology should not
lead us to dismiss as meaningless the claim that bats and Martians
have experiences fully comparable in richness of detail to our own.
It would be fine if someone were to develop concepts and a theory
that enabled us to think about those things; but such an understanding
may be permanently denied to us by the limits of our nature.
My realism about the subjective domain in all its forms implies a belief in the existence of facts beyond the reach of human concepts ...simply because our structure does not permit us to operate with concepts of the requisite type.
Reflection on what it is like to be a bat seems to lead us, therefore, to the conclusion that there are facts that do not consist in the truth of propositions expressible in a human language. We can be compelled to recognize the existence of such facts without being able to state or comprehend them.
Whatever
may be the status of facts about what it is like to be a human being,
or a bat, or a Martian, these appear to be facts that embody a particular
point of view.
The point of view in question is not one accessible only to a single
individual. Rather it is a type. It is often possible to take up
a point of view other than one's own, so the comprehension of such
facts is not limited to one's own case. There is a sense in which
phenomenological facts are perfectly objective: one person can know
or say of another what the quality of the other's experience is.
The more different from oneself the other experience is, the less
success one can expect with this enterprise.
In speaking
of the move from subjective to objective characterization, I wish
to remain noncommittal about the existence of an end point, the
completely objective intrinsic nature of the thing, which one might
or might not be able to reach. It may be more accurate to think
of objectivity as a direction in which the understanding can travel.
If we acknowledge that a physical theory of mind must account for
the subjective character of experience, we must admit that no presently
available conception gives us a clue how this could be done. The
problem is unique. If mental processes are indeed physical processes,
then there is something it is like, intrinsically, to undergo certain
physical processes. What it is for such a thing to be the case remains
a mystery.
What moral should be drawn from these reflections, and what should
be done next? It would be a mistake to conclude that physicalism
must be false. Nothing is proved by the inadequacy of physicalist
hypotheses that assume a faulty objective analysis of mind. It would
be truer to say that physicalism is a position we cannot understand
because we do not at present have any conception of how it might
be true. Perhaps it will be thought unreasonable to require such
a conception as a condition of understanding. After all, it might
be said, the meaning of physicalism is clear enough: mental states
are states of the body; mental events are physical events. We do
not know which physical states and events they are, but that should
not prevent us from understanding the hypothesis. What could be
clearer than the words 'is' and 'are'?
But I believe it is precisely this apparent clarity of the word 'is' that is deceptive. Usually, when we are told that X is Y we know how it is supposed to be true, but that depends on a conceptual or theoretical background and is not conveyed by the 'is' alone. We know how both "X" and "Y " refer, and the kinds of things to which they refer, and we have a rough idea how the two referential paths might converge on a single thing, be it an object, a person, a process, an event or whatever. But when the two terms of the identification are very disparate it may not be so clear how it could be true. We may not have even a rough idea of how the two referential paths could converge, or what kind of things they might converge on, and a theoretical framework may have to be supplied to enable us to understand this. Without the framework, an air of mysticism surrounds the identification.
This explains the magical flavor of popular presentations of fundamental scientific discoveries, given out as propositions to which one must subscribe without really understanding them. For example, people are now told at an early age that all matter is really energy. But despite the fact that -'they know what 'is' means, most of them never form a conception of what makes this claim true, because they lack the theoretical background.
At the present time the status of physicalism is similar to that which the hypothesis that matter is energy would have had if uttered by a pre-Socratic philosopher. We do not have the beginnings of a conception of how it might be true. In order to understand the hypothesis that a mental event is a physical event, we require more than an understanding of the word 'is'. The idea of how a mental and a physical term might refer to the same thing is lacking.
Very little work has been done on the basic question whether any sense can be made of experiences' having an objective character at all. Does it make sense, in other words, to ask what my experiences are really like, as opposed to how they appear to me? We cannot genuinely understand the hypothesis that their nature is captured in a physical description unless we understand the more fundamental idea that they have an objective nature.
I should like to close with a speculative proposal. It may be possible to approach the gap between subjective and objective from another direction. Setting aside temporarily the relation between the mind and the brain, we can pursue a more objective understanding of the mental in its own right. At present we are completely unequipped to think about the subjective character of experience without relying on the imagination—without taking up the point of view of the experiential subject. This should be regarded as a challenge to form new concepts and devise a new method—an objective phenomenology not dependent on empathy or the imagination. Though presumably it would not capture everything, its goal would be to describe, at least in part, the subjective character of experiences in a form comprehensible to beings incapable of having those experiences.
We would have to develop such a phenomenology to describe the sonar experiences of bats; but it would also be possible to begin with humans. One might try, for example, to develop concepts that could be used to explain to a person blind from birth what it was like to see. One would reach a blank wall eventually, but it should be possible to devise a method of expressing in objective terms much more than we can at present, and with much greater precision. Structural features of perception might be more accessible to objective description, even though something would be left out.
Apart
from its own interest, a phenomenology that is in this sense objective
may permit questions about the physically basis of experience to
assume a more intelligible form. Aspects of subjective experience
that admitted this kind of objective description might be better
candidates for objective explanations of a more familiar sort. But
whether or not this guess is correct, it seems unlikely that any
physical theory of mind can be contemplated until more thought has
been given to the general problem of subjective and objective. Otherwise
we cannot even pose the mind-body problem without sidestepping it.