What Is Consciousness?

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What Is Consciousness?
Getting a handle on the amazing inner movie all of us enjoy

What The Brain Does and How it Does It

One way of thinking about the brain is as the command centre of the body. It is an incredibly complicated input-output system which regulates and controls much of what is going on in the body. The brain plays a crucial role in both behavior control and maintaining the balance of the various organ functions. It is responsible for consciously controlled actions, such as grabbing an object in front of you, as well as unconscious regulation, such as narrowing your blood vessels in reaction to temperature drops around you to minimize temperature loss and causing muscles around your vital organs to shake in small movements in order to generate warmth.

The job-description of the brain is impressive, it contains a huge number of functions. And some of the individual tasks and functions are just by themselves mind-bogglingly complicated and demanding. In recent years we’ve learned much about the structure of the amazing organ which is versatile enough to cover such a vast range of tasks. Many of the mechanisms which make up the brain and are collectively responsible for its functions have been discovered and described. What we figured out so far, in a nutshell, is this: On a fairly fundamental level, the brain consists of billions of neurons (one of the recent estimates is around 68 billion neurons). These neurons are connected to each other by protoplasmic fibers called axons, and use this connection to transmit signals to each other. These events of communication are called action potentials. Given the right kinds of connections between these neurons, they participate in an incredibly complex, orchestrated collective activity to create the necessary output to “run” the human body.

These are the basics, and although they may sound fairly straightforward, we are still far away from explaining many aspects of the brain’s function and human behavior in terms of neural activity. Neuroscience, as it is being practiced today, relies heavily on multi-level explanations. Some explanations of spatial memory for example invoke entities and mechanisms at various levels and of various sizes: They mention parts of the experimental setup, for example a water maze, and certain brain areas which are responsible for the functions in question, for example the Hippocampus, which is responsible for generating a spatial map. How the Hippocampus manages this feat may be explained in terms of long-term potentiation in hippocampal synapses (Craver 2007, p.165 ff.). So in a satisfying explanation of spatial memory, all sorts of levels may play explanatory roles.

It is important to note that invoking levels of explanations does not mean that the brain is something very special and can’t, in principle, be reduced to and explained in terms of fundamental physics. It just means that the fundamental explanation is so complicated and difficult to both get at and understand, that we may not have it for a long time and that, even if we had it, it might be of very limited use to us. Given our limited computational abilities, higher-level explanations are often much more illuminating. And neither does the necessity of multi-level explanations mean that we do not know, in principle, how neural systems can perform the various higher-level functions of the brain. We actually understand the explanatory value and the functions of neural networks well enough so that we already began to imitate them to solve various problems.

The Big Surprise: Our Inner Movie

The last section contained a very rough sketch of what the brain does and how it does it. Nothing has been said that gives us any reasons to believe that the brain is somehow special among all the objects of scientific study. Granted, it is much more complex than, say, the liver or the CPU in a computer, but the same basic explanatory principles apply: we identify a certain function as a phenomenon to be explained and then figure out which mechanisms collectively perform that function.

What makes the brain really special is not its complicated function. It is what may deserve to be called our biggest scientific surprise: the brain’s performing these various functions is accompanied by an amazing “inner movie”. Each of us is intimately familiar with this movie: it contains our visual field, our tactile experience, and all of our other sensory experiences. The movie captures what it is like to have these sensory experiences from the first-person perspective. But this is not all: curious as it may sound, the movie also captures our thoughts and the content of our imagination. We know what imagining being on Mount Everest feels like and we know what calculating the sum of 2+2 feels like simply from enjoying this inner movie. We also know our own moods and emotions this way. We don’t have to look in a mirror to see whether we are sad, we simply feel it; it is part of our subjective inner movies. These elements of our inner movies do not come as individual fragments, they come in groups or packages we usually call subjects. The fact that our experiences are bound together and grouped in such a way is usually called the unity of consciousness.

It is difficult to feel surprised by the existence of countless inner movies accompanying the various brains in the universe. The reason is simply that we are so used to experiencing these inner movies. We knew about these movies long before we knew anything about the brain. The subjective character and feeling of experience is better known to us than anything else, and our knowledge of the external world is mediated by this subjective experience. Another way of putting it is to say that we have privileged access to our own mental life and our own experiences, we know about them in a more immediate and intimate way than we know about the world around us, or even our own bodies.

Philosophers have called the subjective feeling of all our experiences qualia, sentience, phenomenology, or phenomenal consciousness. Some elements of our subjective experience, for example what it feels like to think and do cognitive tasks, have their own names, in this case cognitive qualia or cognitive phenomenology. In this post we will simply use the term “consciousness” to refer to all subjective experience.

The Science of Consciousness: Four Challenges

Consciousness is baffling in ways other objects of scientific study, including brains, are not. In what follows we identify and describe some of the main challenges in the scientific and philosophical study of consciousness.

Explaining Consciousness

Although we still lack explanations of various functions of the brain, the basic principles and methods of brain-explanations are sufficiently clear: we identify a certain phenomenon, a function which is performed by the brain, and show which mechanism or mechanisms individually or collectively perform that function (Craver 2007, p. 6 f. and Chalmers and Jackson 2001). The prospects for making progress by applying this method are good. This is why the philosopher David Chalmers had dubbed these problems the easy problems of consciousness.

Explaining the subjective character of consciousness on the other hand seems much harder. It is not clear at all that the methodology we use to solve the easy problems works to explain consciousness. After all, this inner movie is at least not obviously a function which we can describe in functional terms, the way e.g. digestion can be described in functional terms as the breaking down of food into smaller components that can more easily be absorbed and assimilated by the body. Therefore, it is not clear how we could start the inquiry to find the mechanisms which satisfy these functions. This is why Chalmers has labeled it the hard problem of consciousness.

Various explanatory strategies have been suggested, and they can be classified into several distinct groups. Here we mention only two (the others can be found in Chalmer 2012, p. 111 ff.). One type of strategy centers around the view that once we’ve explained all the functions of the brain in terms of mechanisms, we have explained everything there is to explain. Some adherents of this view deny that consciousness exists, they claim that consciousness is just an especially stubborn illusion. Others accept that consciousness exists but think it can be wholly described in terms of functional concepts, namely those describing the various brain functions, such that we can pursue the usual explanatory strategy of finding (neural) mechanisms. Another type of strategy wants to explain consciousness not by reducing it to something else, but by positing it as fundamental, alongside certain physical quantities such as perhaps mass or charge (or whatever our ultimate physical theory will posit as fundamental). On this view, a theory of consciousness posits it as fundamental and then elucidates and describes its character and how it is related to other fundamental properties.

Measuring Consciousness

What makes us so certain that consciousness exists? Our privileged access to our own consciousness is also what makes it so difficult to measure and quantify consciousness. It seems that we cannot observe other beings’ consciousness the same way we can observe our own consciousness, or even the way we observe ordinary physical events.

We can distinguish two distinct questions that are both concerned with measuring consciousness. One is how we figure out whether certain physical processes, such as cognition in a brain, are accompanied by consciousness at all. The other is how we determine what the character of a given state of consciousness is.

Both questions are of significant practical and theoretical importance. They are of theoretical importance because finding the right explanation of consciousness might depend crucially on reliable measurements of consciousness, just as any other theory in the natural sciences rely on accurate measurements. But they are also of practical importance because certain states of consciousness – those associated with pain and happiness – are essential to figure out the moral status of various actions. Knowing whether a certain coma patient still has consciousness, and what the character of her experiences are, might make a huge difference to how we want to treat her. Consciousness or sentience might well be the single most important feature when making ethical judgments about cases, and so the ability to reliably measure consciousness or sentience is crucial for our moral practice.

The Distribution of Consciousness

If we could figure out how to reliably measure consciousness, we could move on to settle the distribution question: which physical processes are accompanied by consciousness? The standard view is perhaps that fairly sophisticated brains give rise to consciousness, but everything else doesn’t. A more permissive view accepts that in fact only fairly sophisticated brains have consciousness, but adds that in principle other substrata could have consciousness as well. Perhaps in the not-so-distant future, some machines (AIs) will have consciousness too. A very restrictive view, one sometimes attributed to René Descartes, claims that only human brains enjoy the privilege of consciousness. The most permissive view is that everything has consciousness, that what is different between a thermostat and a human is merely the character of consciousness. A thermostat has only very simple consciousness, perhaps similar to that of a human in a meditative state, seeing only a single color in her visual field. Humans on the other hand often enjoy extremely complex consciousness that combines elements from all senses. This view on the distribution of consciousness is called panpsychism.

This question, although perhaps, because we have a clear understanding of the space of possible solutions, less difficult than the hard problem, is still very difficult. So difficult, that Scott Aaronson calls the distribution question the Pretty-Hard Problem of Consciousness.

It should be noted that it’s not entirely clear that we must first solve the measurement problem before we can move on to answer the distribution question. Perhaps the right methodology is to find an elegant and intuitively plausible answer to the distribution question, and then derive from it what physical features of a system we must look for when trying to find consciousness.

Psychophysics and Correlates of Consciousness

If we knew more about the distribution and character of consciousness, we could start developing psychophysical theories. These theories would capture systematic connections between the character of consciousness and features of the physical world, perhaps using mathematical formalisms. (Psychophysics can be seen as a part of this endeavor, although it is often described more neutrally as the attempt to formally describe the connection between physical processes, such as stimuli, and sensations, not perceptual consciousness.) The model for these theories are theories in physics, where fundamental physical quantities are related to each other, except that now physical quantities are related to elements of consciousness.

A less ambitious project which is also less hostage to progress in measuring consciousness consists in identifying correlates of consciousness: We try to find which elements of the brain are responsible for which elements of conscious experience.

Psychophysics and the search for correlates of consciousness seem to be independent of the project of explaining consciousness. Both physicalists and dualists could in principle agree on a psychophysical theory or on a certain set of correlates of consciousness. They would only disagree about the nature of the phenomenal properties and the laws in psychophysical theories, and on what exactly being a correlate of consciousness means.


This post was a short introduction to the phenomenon of consciousness and some of the challenges associated with it. In future posts we will discuss certain aspects of the debate in more detail, namely the question of the right explanation of consciousness, arguments against the reducibility of consciousness, and arguments for panpsychism.


Chalmers, D. J., & Jackson, F. (2001). Conceptual analysis and reductive explanation. Philosophical Review, 315-360.

Chalmers, D. J. (2010). The character of consciousness. Oxford University Press.

Craver, C. F. (2007). Explaining the brain. Oxford: Oxford University Press.