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Pain

PAIN

There is no consistent philosophical view concerning the nature of pain, how to understand it, or what an understanding of pain might mean for philosophy of mind. Just about every conceivable position concerning the nature of pain is held by some leading thinker. Each of these positions has become grist for someone's mill in arguing either that pain is a paradigm instance of a conscious state or that pain is a special case and should not be included in any general theory of consciousness.

Philosophical Views of Pain

Some philosophers and psychologists hold that pain is completely subjective: Either it is essentially private and completely mysterious, or it does not correlate with any biological markers but is completely nonmysterious. The International Association for the Study of Pain (IASP), the formal organization charged with defining pain, has articulated a paradigm subjective view. They write: "Pain is always subjective. Many people report pain in the absence of tissue damage or any pathophysiological cause; usually this happens for psychological reasons. There is usually no way to distinguish their experience from that due to tissue damage if we take the subjective report. [Pain] is always a psychological state" (1986).

However, if one holds that pain does not correlate in some way with some sort of bodily state or event, one becomes a dualist. If pain just is a private experience, and that experience has no consistent underlying physical cause or correlate, then any interesting connection between the mind and the body over pain is lost.

Philosophers can eschew dualism by retreating to so-called token-token identity theory. Every experience in some creature is correlated withidentical tosome event or other in that creature's brain. And every experience in some other creature is correlated withidentical tosome event or other in that creature's brain. If the subjectivists are right, then there is no identifiable neural activity that is the same across all experiences of a type of pain. There is no brain correlate for the type "having a migraine headache," for example. Generic headache experiences occur only at a level of abstraction above brain activitynamely, in the mind and its cognitive states.

However, if philosophers deny type-type identity for larger brain structures across organisms, then they are also denying any hope of discovering mind-brain connections. For mental event-physical state correlations taken one at a time are all a robust token-token identity theory allows.

At the same time, scientists do believe that there are areas in the brain dedicated to pain processing, just as there are other areas dedicated to vision, audition, touch, and so forth. They believe that these areas are basically the same across humans, despite individual variation. Thus, even though a strict type-type identity might fail for particular sensory experiences, it still underlies views of our sensory systems taken as a whole. Types in science are allowed some play in them. They have to, or else there would be no mechanism by which to pick out any sort of cognitive processing in the brain at all.

All these lessons are missed by proponents of the subjective view, for they identify pain with the experience of pain and then explicitly deny that that experience has any correlation with any particular bodily reaction. But insofar as they want to be materialists interested in a scientific understanding of pain, they will have to permit generalizations connecting something in the body with the sensation of pain (see Hardcastle 1999).

Other philosophers and neurophysiologists argue that pain is completely objective; it is either intrinsic to the injured body part, a functional state, a set of behavioral reactions, or a type of perception. Pain is something that can be measured in bodies or behavior. As such, its connection to mentality, to sensations of pain, is secondary at best. Humans might recognize pain in terms of how it feelsthe skin burns, for example. But, according to objective views that take pain as intrinsic to the injured body part, the pain itself is in the tissue. Hence, beliefs or judgments about the condition of the tissue are derivativethat is, pain is inferred from peripheral nociceptive or pain information (Annad and Craig 1996, Derbyshire 1996).

Similarly, if pain is understood as a type of perceptual process, then it works no differently than vision or olfaction. Animals receive some sort of perceptual input on their transducers, manipulate that information in their brains, and then use that manipulated information to alter motor reactions and other mental states. Part of the manipulated information might come into conscious awareness, but that sensation would constitute only a subset of what is meant by pain processing. According to this view, conscious experiences of pain, the damaged tissue itself, and the bodily and emotional reactions are all fundamental to pain processing. Each is one component in a larger process. Working together, these components take pressure, temperature, and chemical readings of tissues and use this information to track what is happening in bodies (Wall and Melzack 1989).

In these cases and most other instances of the objective view, pain is something entirely physical. Prima facie, it appears that the states or processes identified with pain could occur without any awareness of them at all. Most objective views of pain have the unintuitive consequence of divorcing pain from sensations of pain or making the mental events associated with pain processing secondary to and dependent upon the pain processing itself.

There are a few objectivist philosophers who hold that pain is not a purely physical event. Instead, it is something like an attitudinal relation. Pain requires both a bodily state and then cognition over that state. Pain itself is the attitude, the belief, regarding one's bodily condition. This approach gets around the intuitive difficulties of the objective views by identifying pain with the consequent mental state. "Pain" then just refers to the mental event associated with pain processing. According to this view, there is pain processing and then pain proper.

Central Philosophical Issues

There are three large philosophical difficulties in defending any of the theories about pain processing outlined above: the problem of mental causation, the problem of naturalizing content, and the threat of eliminativism.

The difficulty with mental causation is roughly as follows. If one drops a hammer on one's foot and subsequently experiences pain, that experience is the proximal cause of one's writhing, cursing, and gnashing of teeth. Dropping a hammer on one's foot leads to pain behavior only if it causes in one the sensation of pain and the belief that one is in pain. If one were unconscious or otherwise oblivious to one's surroundings, then one could not sense any pain, nor could one believe that one were in pain. One could manifest no pain-related behavior either.

On the other hand, a neurophysiological view of the hammer-dropping incident seems be able to explain exactly the same events without appealing to mentality or any sort of psychological entities at all. Neurophysiologists might talk about how the intense pressure of the hammer head on a foot stimulates various nerve endings and thus causes action potentials to travel up a leg to a spinal column, where other nerves are then stimulated to fire. These nerves transmit the firing pattern to other nerves, and so it goes until nerves that cause muscles to contract are likewise stimulated and one gets the writhing, wincing, and teeth-gnashing behavior. Why doesn't the possibility of this sort of more precise, purely physical explanation rule out the higher-level, more general mental account? Or why doesn't it make the mental account nothing more than a placeholder until the details of our central nervous system get figured out? As long as one is persuaded by reductionism, then pain provides an exemplar case for why psychological explanations appear so tricky.

There is some evidence that depression is related to pain processing. One view is that untreatable chronic pain causes depression, which in turn increases the sensations of pain. This is a (grossly oversimplified) mentalistic explanation of how a mood causally interacts with other psychological states. At the same time, we know that depression is correlated with a decrease in the neurotransmitter serotonin. Persons suffering from just an imbalance of a neurotransmitter and sensations of pain are some neural state or other, then it seems that the relation between depression and pain should be explained in terms of neurotransmitters affecting neural activity. In this case, the mentalistic explanation is just a stand-in until all the more basic neurphysiological details are revealed.

Mental events causing other mental events seems to be a natural part of the explanatory world. At the same time, accounts of mental causation appear to be nothing over and above a sloppy characterization of more fine-grained and little understood physical details. The difficulty for those who would like to keep the mind intact as an explanatory unit is explicating how it is that mental causation has a legitimate place in an understanding of the universe above and beyond being a surrogate for the real causal story.

Though most philosophers of mind treat mental causation separately from issues concerning reference, explaining the causal powers of the mind really piggybacks on the problem of naturalizing content. What makes the question of mental causality peculiar is that the content of the mental states is relevant to their efficacy. One winces and nurses one's foot because one's corresponding mental states are about one's foot. If they were about something else, then one would most likely be doing something else. To explain exactly how it is that mental events cause other things, philosophers are first going to have to explain how it is they refer. That is, to justify privileging a mentalistic explanation of sensations and beliefs over a lower-level physicalistic one of neuronal firing patterns or ionic flow, first philosophers have to have a clear grasp on what it means to have mental events with content, since their content is what is causally relevant to subsequent behavior.

The question about the power of the content of beliefs and other mental states is quite important to understanding pain processing (Gamsa 1994). What one is thinking and believing about the world strongly influences how much pain one feels. Athletes intently focusing on their game can break large bones and not even notice it. But the same athletes, alone in their living rooms, will writhe on the floor if they stub their toes. Chronic pain patients can be trained to diminish their sensation of pain by changing their focus of attention and their beliefs about death and disease. Those suffering congenital indifference to pain often lead short and unpleasant lives both because they can't sense painful stimuli but also because they cannot form appropriate beliefs about the meaning of the vague tinglings they do feel. How pain feels depends to a large extent on the current doxastic milieu. Hence, understanding pain is going to require understanding what beliefs and desires (and other mental states) are and how they refer.

One implication of current scientific theories of pain is that folk ways of describing pains are inadequate and people would be better off eliminating the descriptors from everyday practices (Dennett 1978). The claim is that folkways of talking about pain comprise a rough and ready theory of pain. This theory assumes that pains are identical to the sensations of pain and that the word pain can capture the essence of that sensation. From the perspective of some objective views of pain, both assumptions are dubious. Pain processing is enormously complicated, and sensations of pain form only a tiny subset of what these processors do. But even if one focuses exclusively on sensations, the most important to folkways of being, the folk theory is still inadequate. Words to express all the dimensions of pain experiences simply do not exist. The descriptors used are either metaphorical or nonexistent. The folk theory of pain needs to be replaced by something commensurate with the phenomenology.

Consider that not only can the sensory, affective, and cognitive dimensions of pain be distinguished phenomenologically, but they can also be manipulated independently of one another. Mammals can feel a shooting pain in their legs but not suffer in the least from it; they can be in agony from pain without feeling any particular sensation localized to any part of their bodies. Philosophers could just decide by fiat that pain is going to refer to the localized sensations, or they could just decide that pain is going to refer to the suffering. But either way they do violence to folk notions of pain, which require that a single simple sense datum both seem to occur in some place and be unpleasant.

In response to these sorts of claims, some have argued that folk views of pain do not constitute a theory in any meaningful sense. Some believe that certain introspective facts are known indubitably. Pain is touted as one of those things. Perhaps there are some sensory states, like pain, about which people have special first-person apprehension; no inference of judgment is required.

However, it is quite easy to demonstrate that introspective knowledge of pain can be mistaken. If one burns one's hand by touching something hot, one jerks one's hand away from the heat source. This is a reflex action; the nociceptive information travels up the arm to the spinal column and then back down again. It takes about 20 to 40 msec from stimulus to behavior. The information also travels up the spinal column to the brain. One feels the burn as well. Unlike the reflex movement, this processing is more complicated and takes about 200 to 500 msec from stimulus to percept, a full order of magnitude longer.

Nevertheless, if one introspectively reports on what the incident feels like, one says that one moved one's hand away after one felt the pain; feeling pain initiated the motor sequence. For whatever reason, brains backdate pain sensations so that they seem causally relevant to reflex behavior. But clearly the effect is not caused after it occurs, so the introspective report has to be wrong. There is not any special, first-person knowledge of pains. Whatever knowledge is had is embedded and informed by a conceptual framework of the brains' devising. Despite protests to the contrary, pain experiences have all the earmarks of being at least prototheoretical in nature.

Other detractors point out that even if a completed science of pain does not use folk terms for pain, that would not imply that those sorts of mental states do not exist; they just would not be referred to in scientific discourse. The notion of pain would be analogous to ideas about tables and chairs, germs and gems, and birthday presents and birthday cake. These are perfectly legitimate terms. Science just does not use them. Being cultural artifacts of one stripe or another, they do not refer to things about which there are laws. There might not be a mental science or laws about pains, but folk psychology could still be used as it is now, in everyday explanations of behavior.

There is something undoubtedly right about this charge. In many ways, pain experiences are environmentally determined. Puppies raised without ever experiencing pain and without ever seeing any other dog in pain will exhibit no pain behavior. They will repeatedly sniff a lighted match without fear and then show no reaction when burned. Children learn both pain behaviors and the emotional concomitants to pain from the reactions of others around them. Expressions of pain and reports of sensation and experience are significantly different across cultures. Most of pain experiences and expressions are socially relative, a cultural artifact of sorts.

However, social relativity is not enough to show that folkways of understanding pain are adequate. Different cultures have different experiences; they also have different ways of understanding these experiences. Nevertheless, the burden falls on the folk psychologist to demonstrate how folk theories of pain are actually successful. This work has not just begun.

The Ethics of Pain Treatment

One of the most hotly debated subjects in pediatric care concerns whether infants are insensitive to pain (cf. Lawson 1988). The presumption historically has been that because young infants are not conscious, they cannot sense pain. As a result, analgesics and anesthesias are rarely used, even in the most invasive of procedures.

At first, this presumption of insensitivity is curious because infants' reactions to painful stimuli are well documented. Even premature neonates exhibit stress responses, hormonal fluctuations, and slowed recovery to painful interventions. In fact, the afferent nociceptive system is up and running by twenty-nine weeks of gestation, even though the pain inhibitory systems do not come on line until later. If anything, infants should be more sensitive to pain than adults. At least, by all indications, infants are sensitive to pain in some sense or other.

However, the question for many doctors is whether infants are aware of their pain. Some argue that unless neonates can consciously apprehend pain, then any sort of response they give to noxious stimuli are merely reflexes. Hence, there is no reason to treat infants' pain because the infants cannot feel anything.

Suppose they are right, even though there is much that goes on in brains that is neither conscious nor mere reflex. It is still the case that infants react to pain, both behaviorally and physiologically, that these reactions can be modified with relatively simple treatments, and that treating pain has an impact on recovery. Early exposure to pain, whether remembered or not, affects later experiences of and reactions to pain by altering the developmental course of the nervous system. Infants, like other newborn animals, learn to attach particular meanings or emotions or importance to particular experiences in virtue of what is associated with those experiences. This sort of behavioral malleability is very important if an organism is going to survive in a complex environment. Consequently, manipulating early experiences can have drastic effects later on, as animal studies show. Merely by changing the smells associated with suckling, scientists can alter adult sexual behavior in male rats, for example. Similar changes occur with pain processing in young infants. Nociceptive stimuli increase the size of the somatic receptive fields for neurons sensitive to pain and help maintain dendritic connections that would otherwise be eliminated over time. Perhaps, as some believe, chronic pain and hypersensitivity can result from early acute pain episodes, given how the neural receptors change. Early pain experiences have been shown to influence later personality and temperament. Something as common as circumcision can have lasting effects on pain sensitivity if done without anesthesia.

Given the impact early pain processing can have on later development, doctors have every reason to prevent infant pain, even if it feels dissimilar to an adult's, even if it feels like nothing at all to the infant. Whether infants consciously experience painand whether they are aware of some noxious stimulus or their own sufferingis a red herring. Available evidence converges around the idea that infants process pain, though perhaps not in the same way adults do. This processing has an impact on current behavior and later development. Because this influence is generally negative, insofar as we are able to prevent or alleviate some of their pain, we should.

See also Qualia.

Bibliography

Anand, K. J. S., and K. S. Craig. "New Perspectives on the Definition of Pain." Pain 67 (1996): 36.

Deberyshire, S. W. G. "Comment on Editorial by Anand and Craig." Pain 67 (1996): 210211.

Dennett, D. C. "Why You Can't Make a Computer That Feels Pain." Synthese 38 (1978): 449.

Gamsa, A. "The Role of Psychological Factors in Chronic Pain, I and II." Pain 57 (1994): 529.

Hardcastle, V. G. The Myth of Pain. Cambridge, MA: The MIT Press, 1999.

International Association for the Study of Pain (IASP). Subcommittee on Classification. "Pain Terms: A Current List with Definitions and Notes on Usage." Pain (supplement) 3 (1986): 217.

Lawson, J. "Pain in the Neonate and Fetus." New England Journal of Medicine 318 (1988): 1, 398.

Wall, P. D., and R. Melzack, eds. Textbook of Pain. 2nd ed. New York: Churchill Livingstone, 1989.

Valerie Gray Hardcastle (2005)

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