Last updated: Wed, Feb 19, 2025
I've been blithely writing along about pain without any worry about whether you and I know what pain is. That is, I assume that we are thinking about the same thing when we communicate about the sensation of pain and its associated effects. That's fine in non-scientific communication, but in the context of science it becomes important to agree just what is and what is not pain.
There is an organization, the International Association for the Study of Pain (their website) "that promotes pain research, education, and advocacy." Its members are mostly people with a medical and/or a scientific interest in pain. They provide a definition of pain along with commentary on it that is widely-quoted in the pain literature.
They define pain as
an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.1
This definition goes back at least to 1986. Melzack and Wall have criticized this definition for the term "unpleasant."2 They complained that the term hides the severity and also the complexity of pain's unpleasantness. A definition, however, isn't intended to be a full description. In the scientific context, it separates experiential phenomenon into two categories: pain and not-pain.
The IASP-endorsed definition characterizes pain itself as a sensory and emotional "experience" rather than as a physiological process. This hasn't been done because of a lack of awareness that there are physiological processes involved. Instead, it says that pain exists when a person's experience is in some way "associated with" tissue damage, actual or potential, or when the experienced is "described" in terms of actual or potential tissue damage. Does that sound a little mysterious?
There is a lot of mystery surrounding pain. Although pain is frequently cited as a simple and straightforward example of the functioning of the nervous system, a number of major questions reveal themselves when pain is looked at from a broad perspective. As I pointed out in a prior section, your pain is visible to you but is only heard about by others. Nobody knows from their personal experience whether another's pain experience is like their own, even in similar situations. The mechanisms of pain are complex and confusing. The stakes of pain are large. Estimates of pain's money cost are typically in the multiple billions of dollars per year. Some methods of pain treatment are hazardous, others are expensive.
Pain care providers must routinely make judgments about the severity of their patients' medical conditions, so these ambiguities are omnipresent in their daily experience. If the care provider can't observe or infer tissue damage or other pathologies in a patient, but hear reports of severe suffering, what are they to do?
The IASP follow their pain definition with a long explanatory note:
Note: The inability to communicate verbally does not negate the possibility that an individual is experiencing pain and is in need of appropriate pain-relieving treatment. Pain is always subjective. Each individual learns the application of the word through experiences related to injury in early life. Biologists recognize that those stimuli which cause pain are liable to damage tissue. Accordingly, pain is that experience we associate with actual or potential tissue damage. It is unquestionably a sensation in a part or parts of the body, but it is also always unpleasant and therefore also an emotional experience. Experiences which resemble pain but are not unpleasant, e.g., pricking, should not be called pain. Unpleasant abnormal experiences (dysesthesias) may also be pain but are not necessarily so because, subjectively, they may not have the usual sensory qualities of pain. Many people report pain in the absence of tissue damage or any likely 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. If they regard their experience as pain, and if they report it in the same ways as pain caused by tissue damage, it should be accepted as pain. This definition avoids tying pain to the stimulus. Activity induced in the nociceptor and nociceptive pathways by a noxious stimulus is not pain, which is always a psychological state, even though we may well appreciate that pain most often has a proximate physical cause.
These explanatory notes don't clarify the pain definition for me. They suggest to me that the IASP definition was formulated with awareness of the uncertainties faced by pain care providers and indirectly by researchers. In fact, there has been a very large number of words written in an attempt to deal with the mystery and uncertainty surrounding pain complaints, the lack of clear medical findings, and the situation of pain describers whose care providers haven't found a medical cause for their complaints.
"Pain is always subjective." This is not part of the IASP pain definition, but is an assertion about the nature of pain. As I look at a dictionary definition of "subjective" (Wiktionary) I see that there are seven different definitions. Which of these definitions are we meant to apply in understanding the IASP's assertion about the nature of pain? Perhaps defintion 6, which applies to philososphy and psychology: "Experienced by a person mentally and not directly verifiable by others." But perhaps definition 4, "Lacking in reality or substance" might be understood. These two definitions are not at all congruent in my experience. My pain is very real and substantial. They might have said instead that "Pain is not directly observable except by the person who experiences it." That statement is not ambiguous.
The term "psychological" occurs twice in their notes. ''Many people report pain in the absence of tissue damage or any likely pathophysiological cause; usually this happens for psychological reasons." First I must point out that this assertion is un-scientific because it is neither verifiable nor refutable. The absence of any "tissue damage" or "likely pathophysiological cause" could only be established if all possible damages or other causes 1) were known, and 2) could be detected by medical practice, and this is simply not the case. If it is not possible to eliminate all possible "non-psychological" causes, it is also not possible to know how many people might be in this condition. But second, what is meant here by "psychological reasons?" Psychology as a scientific discipline or as a set of beliefs about human nature has worn many different feathers even during my own lifetime. The IASP comments originated as long ago as 1994, at a time when neuroscientific research was only beginning to challenge tenets of the psychological community and far before those challenges could begin to affect psychological views of pain.
Later they state that, "Activity induced in the nociceptor and nociceptive pathways by a noxious stimulus is not pain, which is always a psychological state," Here it seems to me that the meaning of "psychological" may be more clear. By "psychological state," they may mean the state of the nervous system. Such a view is consistent with my own, but I do believe that the term "psychological," just like the term "subjective," has a broad range of meanings.
I believe that these questions about meanings deserve our attention because words with broad meanings allow and perhaps facilitate unclear thinking. When our view of reality is unclear, it allows non-scientific ideas to comfortably exist and to affect behaviors. This affects the lives of pain sufferers in important ways, as I attempt to make clear throughout this text. The next major section of this work, How We Understand Pain, makes the case that there are many ways to understand, and that our most natural ways of understanding are prone to mis-understanding when dealing with complex and important questions.
The somewhat mysterious nature of pain (a sensation, a perception) has concrete effects on how and to what extent even the best-informed are able to understand it. Some of these effects are described in Pain Measurement and Pain Research.
I relate my version of the story of "psychological" versus "neuroscientific" understandings of pain in A Rational Model of Emotion and Pain, particularly in Freudian Theories and Behaviorist Theories of Pain and a Standard Model.