The Riddle of Consciousness



“Can you prove you’re self-aware?”

“That’s a difficult question, Dr. Tagger. Can you prove that you are?”


(© 2014 Warner Bros. / Alcon Entertainment, fair use)


We now know that many animals are highly intelligent, with the capabilities to solve problems, communicate, and form societies and cultures. Meanwhile, artificial intelligences grow ever more complex, with some already passing for human in conversation. And as space exploration continues to expand the frontiers of human knowledge, astrobiologists are hopeful that alien life – and perhaps even civilization – will be discovered in the near future.

It is only natural to feel amazement and admiration toward such incredible beings, both those we coexist with now and those we may encounter in the future. But should we feel concern for them? Does the intelligence of animals, aliens, or AIs mean anything for how we should treat them? The answers to such questions hinge on an even more fundamental one: Are such beings conscious?

What is consciousness?

The ability to recognize oneself in a mirror has often been cited as evidence for self-awareness. Only a few non-human animals can pass the test: great apes, elephants, dolphins, magpie birds, and most recently manta rays. Most will either react as if to another animal, or ignore the mirror entirely. Rhesus monkeys normally fail the test, but have been successfully trained to recognize themselves. Does this imply that they became self-aware through teaching, or that they always were and simply lacked the skill to interpret a mirror? Does the cognitive ability to distinguish "self" and "other" necessarily show a subjective experience of consciousness? Do animals that fail the mirror test really lack self-awareness, and if so, does this necessarily mean they aren't conscious at all? (Photo courtesy Dr. Neng Gong, from <a href="">Chang et al. 2015</a>) 300w" sizes="(max-width: 800px) 100vw, 800px" /> Rhesus monkey passing the mirror test for self-recognition (Photo courtesy Dr. Neng Gong, from Chang et al. 2015)

You may have an intuitive sense of what it means to be conscious. After all, your very experience of life depends on it! But can you define it? If not, you’re not alone – scientists and philosophers have struggled to do so for centuries (sometimes using the word “sentience” instead). Even now, there are a range of possible definitions to choose from:

“Consciousness: The fact of awareness by the mind of itself and the world.”

(Oxford English Dictionary)

“Consciousness is the subjective state of feeling or thinking about objects and events.”

(Donald R. Griffin, zoologist, “Evidence of Animal Consciousness”)

“Sentience… a convenient, if not strictly accurate, shorthand for the capacity to suffer or experience enjoyment or happiness.”

(Peter Singer, animal rights philosopher, “Practical Ethics”)

“The fact that an organism has conscious experience… means, basically, that there is something it is like to be that organism… something it is like for the organism. We may call this the subjective character of experience.”

(Thomas Nagel, philosopher, “What Is It Like To Be a Bat?”)

"If we grant that some animals are capable of perceptual consciousness, we need next to consider what range of objects and events they can consciously perceive. Unless this range is extremely narrow, the animal's own body and its own actions must fall within the scope of its perceptual consciousness. ... If animals are capable of perceptual awareness, denying them some level of self-awareness would seem to be an arbitrary and unjustified restriction." (Donald R. Griffin, Animal Minds: Beyond Cognition to Consciousness - photo credit: Greg Auger, © Bat Research News 45, no. 1 (Spring 2004), used with permission) 424w" sizes="(max-width: 154px) 100vw, 154px" /> Zoologist Dr. Donald R. Griffin (1915-2003) argued that many species are conscious and therefore self-aware
"Higher cognitive powers like language, the capacity to keep secrets, to have knowledge of the demands of the social environment, to judge the motives of others, and to evaluate the consequences of behavioral alternatives in advance are all prerequisites for consciousness in order to get positive fitness value. ... Consciousness may therefore only be expected in animals which show these higher cognitive capacities in their behavior. For the experience of emotional feelings, further knowledge of 'self' is required. Since these capacities have, up to now, only been recorded in the anthropoid apes, they are the only species in which consciousness and suffering may be expected." (Bob Bermond, "A Neuropsychological and Evolutionary Approach to Animal Consciousness and Animal Suffering") 353w" sizes="(max-width: 164px) 100vw, 164px" /> In his entry to the volume The Animal Ethics Reader, psychologist Dr. Bob Bermond argues that since few animals are clearly self-aware, few are conscious at all

At a minimum, most seem to agree that consciousness involves awareness and subjective experience. Some experts distinguish between two different types of consciousness: phenomenal or feelings consciousness, awareness of sensations, thoughts, and emotions; and self-consciousness or self-awareness, knowledge of oneself as a unique thinking, feeling individual. Not all agree, however. Some hold that awareness of one’s thoughts and feelings first requires awareness of oneself, meaning that all consciousness is by definition self-consciousness.

Even within the latter camp, there are strong divisions. Some claim that most animals are self-conscious, since many species show signs of subjective thoughts and feelings and so must also be self-aware. Others argue that since only a few species show direct evidence of self-awareness, most animals are not actually conscious at all.

Scientists and philosophers have long struggled to define consciousness. Most agree it involves subjective experience and awareness. Researchers differ as to which, if any, animals are self-aware, and whether they could be conscious without self-awareness.

Why does it matter?

"The day may come, when the rest of the animal creation may acquire those rights which never could have been withholden from them but by the hand of tyranny. The French have already discovered that the blackness of the skin is no reason why a human being should be abandoned without redress to the caprice of a tormentor. It may come one day to be recognized, that the number of the legs, the villosity of the skin, or the termination of the os sacrum, are reasons equally insufficient for abandoning a sensitive being to the same fate. .... The question is not, Can they reason? Nor, Can they talk? But, Can they suffer?" (Jeremy Bentham, The Principles of Morals and Legislation (1789), Chapter XVII, Section 1) 300w" sizes="(max-width: 900px) 100vw, 900px" /> “Portrait of Jeremy Bentham” by Henry William Pickersgill (1829) (Source: Wikimedia Commons / cropped from original)

“The question is not ‘can they reason?’ Nor ‘can they talk?’ But ‘can they suffer?'”

(Jeremy Bentham, 1748-1832)

Read any book or website on animal rights and there’s a high chance you’ll come across the above quote, from philosopher Jeremy Bentham. Animal rights activists believe that animals deserve moral consideration from humans, not because of their intelligence, usefulness to humans, or importance to the ecosystem, but because they are conscious beings who care how they are treated.

In commercial dairy farming, calves are separated from their mothers within a few days of birth, to ensure a large surplus of milk to sell to human consumers. Studies on separated calves show impaired learning, diminished social behavior, and other symptoms consistent with emotional trauma. Other studies have described apparent symptoms of post-traumatic stress disorder in adult cattle who've survived wolf attacks. (Photo credit: <a href="">burnt in effigy</a>, used under <a href="">CC BY-NC 2.0</a> / cropped from original) 755w" sizes="(max-width: 244px) 100vw, 244px" /> Dairy cow and calf at Minnesota State Fair. Calves show signs of emotional trauma when separated from their mothers.

If you have ever had a pet animal, you probably take it for granted that they feel pain. Neuroscience confirms this intuition. Most vertebrates (including mammals, birds, reptiles, and fish) respond to pain in similar ways, and share the name neural structures and chemicals for processing it. Some invertebrates, including octopuses, crustaceans, spiders, and even earthworms, show symptoms of pain as well. Of course, not all pain is physical: emotional distress, and even long-term trauma, is well-documented in many animals as well.

However, there is a difference between the sensation of pain and the perception of suffering. Sensation is a purely mechanical process. Machines can be programmed to “feel” “pain,” that is to sense harmful stimuli and take action to escape it. But if their defenses fail, there’s no reason (yet, at least) to think they experience agony or dread over being harmed.

What colors do you see on this dress? This photograph took the internet by storm in February 2015, sowing discord between those who perceived it as white and gold and those who saw blue and black. The correct answer is in fact blue and black, but the fact that so many viewers don't see those colors illustrates how differently individuals may perceive the same stimuli. (Photo credit: Caitlin McNeill)
Sensation vs. perception: What colors are this dress?

Suffering, on the other hand, is a matter of perception, or subjective experience. Only conscious beings can perceive pain as suffering. But for that matter, not all conscious beings perceive the same sensations the same way. When it comes to pain, the same sensation might cause unbearable suffering for one, mild annoyance for another, and even pleasure for a masochist, while people with certain types of brain injury may not perceive it at all.

We cannot say, then, that just because something feels pain it necessarily suffers. If animals, aliens, or AIs are not conscious, they cannot suffer, and their pain doesn’t matter in any moral sense. But if they do suffer, then their pain matters a great deal, at least from their own perspective. If we place ethical value on others’ experiences, then their pain should matter to us as well. This is why consciousness is so important.

Pain and suffering are not the same thing. Pain is simply a physical response to injury, while suffering is a conscious experience. Because suffering requires consciousness, the question of which beings are conscious carries enormous moral significance.

Why is it unknowable?

"I was thinking about the things I've been feeling, and I caught myself feeling proud of that. Proud of having my own feelings about the world, like the times I was worried about you, things that hurt me, things I want. And then I get this terrible thought, like are these feelings even real? Or are they just programming? And that idea really hurts. And then I get angry at myself for even having pain. What a sad trick." "You feel real to me, Samantha." (Samantha, an artificially intelligent computer, and Theodore, her human "owner," in the movie Her - © 2013 Warner Bros. / Annapurna Pictures, <a href="">fair use</a>)
In the movie Her, a human man and his computer’s artificially intelligent operating system fall in love. Human and AI alike each struggle to understand whether their emotions and relationship together are “real” or not. (© 2013 Warner Bros. / Annapurna Pictures, fair use)

Let us revisit the Turing test. Earlier on, you spoke to another entity via text message, and had to guess whether you were conversing with a human or an artificial intelligence (spoilers ahead – go here if you skipped that part of the exhibit).


Your conversation partner turned out to be an AI, specifically Cleverbot. Cleverbot is one of the world’s most advanced AIs. A powerful offline version of the software has almost passed the Turing test, convincing people that it’s human with nearly the same rate of success as actual human beings.

"You're not kidding, little buddy. I don't like the feel of this place either." "Your droid is programmed to feel?" "R2 is kind of a special case. He just has a lot of personality, that's all." "You encourage it too much." (Jedi Anakin Skywalker, to droid R2-D2, and Mace Windu, in Star Wars: The Clone Wars episode "R2 Come Home" - image © 2010 Disney-ABC / Lucasfilm, <a href="">fair use</a>) 300w" sizes="(max-width: 262px) 100vw, 262px" /> In the Star Wars franchise, droids are programmed to behave as if conscious, yet are disregarded as such even by most Jedi

You probably assume that other humans are conscious, because in general they probably act similar to you in other ways and, if you should ask, will tell you that they are. But is it safe to assume the same of Cleverbot? Does the fact that Cleverbot can talk like a human (at least sometimes) mean that it’s conscious like one?

Probably not. Cleverbot works by comparing what users say to a database of millions of lines of text, from which it selects the closest matching response. With each new conversation, it adds new material to its database, improving its ability to say the right thing in any given context. With a database large enough to contain every possible response to every conceivable statement, an AI like Cleverbot could hold its own in any conversation by purely mechanical means. It would appear to be conscious, without any need for actual consciousness.

In a July 2015 experiment led by Dr. Selmer Bringsjord of New York's Rensselaer Polytechnic Institute, three robots were presented with a variant of the classic "wise men" riddle. Two out of three were programmed to be mute. All three were informed of this fact, and asked to deduce which one was not mute. The robot on the right stood up, said "I don't know," then corrected itself, realizing that because it had spoken out loud it must be the non-mute one. The researchers describe this experiment as a "mathematically verifiable awareness of the self," similar in purpose to the Mirror Test. But can we verify whether or not the robot has a subjective experience of consciousness? (screenshot from <a href="">YouTube</a>, <a href="">fair use</a>)
Three robots in a 2015 experiment designed to test for self-awareness. The one on the right can distinguish “self” and “other” – does this mean it’s conscious?

Some philosophers would refer to Cleverbot as a “zombie.” Obviously this isn’t literal, for the AI lacks a flesh-and-blood body to die, let alone become undead. In philosophy, a “zombie” is a being that lacks any subjective experience, and is therefore not conscious, but simulates every observable sign of it. It illustrates that while we can observe evidence another being is probably conscious, the only way to know for sure is to be that creature oneself. Because it can only be experienced subjectively, consciousness is therefore inherently unprovable.

Could all seemingly conscious non-human beings be zombies? For that matter, might all other humans be as well? Could you yourself be the only conscious being in the entire universe? Technically, there’s no way to prove otherwise.

While consciousness is extremely important, both morally and scientifically, due to its subjective nature it cannot actually be proven to exist. At best, deciding whether another being is conscious is a matter of educated inference rather than hard fact.

Shifts in science

Speakers at the Francis Crick Memorial Conference at the University of Cambridge line up to sign the Cambridge Declaration on Consciousness, which states that "the weight of evidence indicates that humans are not unique in possessing the neurological substrates that generate consciousness. Non-human animals, including all mammals and birds, and many other creatures, including octopuses, also possess these neurological substrates." 300w" sizes="(max-width: 960px) 100vw, 960px" /> July 7th, 2012 signing of the Cambridge Declaration on Consciousness (Photo credit: Dr. Randal Koene)
"Although there are many animals which exhibit more dexterity than we do in some of their actions, we at the same time observe that they do not manifest any dexterity at all in many others. Hence the fact that they do better than we do, does not prove that they are endowed with mind, for in this case they would have more reason than any of us, and would surpass us in all other things. It rather shows that they have no reason at all, and that it is nature which acts in them according to the disposition of their organs, just as a clock, which is only composed of wheels and weights is able to tell the hours and measure the time more correctly than we can do with all our wisdom. ...Next to the error of those who deny God... there is none which is more effectual in leading feeble spirits from the straight path of virtue, than to imagine that the soul of the brute is of the same nature as our own..." (Rene Descartes, Discourse on Method - image: “Portrait of Rene Descartes” by Frans Hals (1582/3-1666), from Wikimedia Commons)
Descartes believed body and mind were separate, and that only humans possessed the latter

Consciousness can be experienced, but not directly observed. For this reason, many thinkers through history have believed it exists apart from nature. René Descartes (1596-1650) coined the term mind-body dualism, separating thoughts and feelings from the workings of the body. Like Aristotle and theologians before him, Descartes believed only humans possessed a mind. Animals were merely natural automata, machines operating by purely physical principles, devoid of thought or feeling. Descartes promoted vivisection, dissection of live animals, dismissing their expressions of pain as mere automatic reactions.

"One should not vent one's wrath on animals. Theology decrees that man has a soul and that the animals are mere automata mechanica, but I believe they would better advise that animals have a soul and that the difference is in its nobility. ... But I ask you and the whole world for a generic differentia between man and ape which conforms to the principles of natural history. I certainly know of none. ... If I were to call man ape or vice versa, I should bring down all the theologians on my head. But perhaps I should still do it according to the rules of science." (Carl Linnaeus, Diaeta Naturalis (1738) and letter to Johann Gmelin (1747). Image: "Carolus Linnaeus in Laponian costume," by Hendrik Hollander (1853), from <a href="">Wikimedia Commons</a>)
Linnaeus believed animals shared a common ancestry with humans, possessing minds and even souls of their own

Though Descartes was highly influential for early modern science, his views on animals were not universally accepted. Biologists Carl Linnaeus (1707-1778) and Charles Darwin (1809-1882) argued that humans are biologically related to other animals. Human abilities, including consciousness, should therefore be found in other species as well.

Descartes believed animals were not conscious, and Linnaeus and Darwin believed they were. But the scientific method relies on empirical testing, and because consciousness is not directly testable, some researchers came to believe it was not relevant to science. Because subjective experiences were unprovable, they considered them unimportant.

"For a consistent investigator there is in the higher animals only one thing to be considered - namely, the response of the animal to external impressions... Strictly speaking, natural science is under an obligation to determine only the precise connection which exists between the given natural phenomenon and the responsive faculty of the living organism with respect to the phenomenon - or, in other words, to ascertain completely how the given living object maintains itself in a constant relation with its environment." (Ivan Pavlov - image: Ivan Pavlov operating on a dog, from <a href=""></a>) 620w" sizes="(max-width: 207px) 100vw, 207px" /> Ivan Pavlov believed the issue of consciousness, either in animals or humans, was scientifically unimportant

Ethically, this position served to justify widespread experimentation on animals, whose kinship with humans made them useful as medical models, without having to consider any moral dilemmas it might pose. Some scientists, such as biologist Ivan Pavlov (1849-1936) and psychologist B. F. Skinner (1904-1990), extended the same philosophy to human beings. They believed human behavior could be similarly explained in purely mechanical terms.

"As we try to come to grips with the emotions of beings progressively more different from ourselves the task, obviously, becomes more difficult. If we ascribe human emotions to non-human animals we are accused of being anthropomorphic - a cardinal sin in ethology. But is it so terrible? If we test the effect of drugs on chimpanzees because they are biologically so similar to ourselves, if we accept that there are dramatic similarities in chimpanzee and human brain and nervous systems, is it not logical to assume that there will be similarities also in at least the more basic feelings, emotions, moods of the two species?" (Jane Goodall, Through a Window, p.16 - photo credit: <a href="">Think Out Loud</a>, used under <a href="">CC BY-NC 2.0</a>)
Jane Goodall’s 1960 discovery of tool use by chimpanzees triggered a revolution in scientific study of animal intelligence

While scientists still cannot test for consciousness directly, the idea that it can’t be studied at all has lost favor in recent years. Jane Goodall’s 1960 discovery that chimpanzees use tools forced scientists to reconsider what other animals are capable of. Many mental abilities once thought unique to humans are now known in other species as well (See Among Us Already…). Advances in neuroscience now permit greater study of consciousness in humans, who can report what they are conscious of, linking conscious experience to types of brain activity seen in other species as well. Simpler experiments such as the Mirror Test can be used to infer self-awareness, a type of consciousness.

Many scientists now believe that consciousness can be reasonably expected of animals that show similar behavior and neurological activity to humans. The highly publicized signing of the Cambridge Declaration on Consciousness on July 7th, 2012 may come to be remembered as a paradigm shift in scientific opinion. Drafted by leading neuroscientists from NeuroVigil, Inc., Washington State University, Hunter College, Bennington College, the University of Queensland, and the Allen Institute for Brain Science, it reads:

“We declare the following: ‘The absence of a neocortex does not appear to preclude an organism from experiencing affective states. Convergent evidence indicates that non-human animals have the neuroanatomical, neurochemical, and neurophysiological substrates of conscious states along with the capacity to exhibit intentional behaviors. Consequently, the weight of evidence indicates that humans are not unique in possessing the neurological substrates that generate consciousness. Non-human animals, including all mammals and birds, and many other creatures, including octopuses, also possess these neurological substrates.‘” Read the entire Cambridge Declaration on Consciousness here.

Historically, scientists have held a range of opinions as to whether non-human animals are conscious, or whether it even matters. While consciousness still cannot be proven to exist, it can now be studied indirectly by various means. Many scientists today believe other animals are probably conscious.

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