How many senses do we have? We often think that we have five. These five senses, also known as the “Aristotelian senses”, are: vision, hearing, taste, smell and touch. However, many scientists and philosophers think that there are more than five: equilibrioception, the sense of balance, is one example. In this entry, I’ll consider whether pain might be a distinct sense.
Fiona Macpherson (2011) highlights four traditional criteria from the philosophical literature that have been used to identify distinct senses: i) representation, ii) phenomenal character, iii), sense organ, and iv) proximal stimulus. As she writes:
I hold that the four criteria are relatively independent dimensions along which different possible kinds of senses could take different values. We can think of these four criteria as defining a multidimensional space within which we can locate each of the Aristotelian senses… Once we have plotted their location in the space and noted their similarities and differences, we have said everything we need to say about the senses. That is when we should cease to ask how to individuate the senses (Macpherson, 2011, p. 37-38).
These four criteria are often used to individuate the senses; however, following Macpherson, instead of focusing only on one criterion, I’ll apply all four criteria to pain and consider the results. Before applying the criteria to pain, to explain them I will focus on vision, which is one of the most studied and discussed senses.
Let’s start with representation. According to this criterion, the senses provide us with different types of information about the way the world is. Vision, for example, is the only Aristotelian sense that provides us with information about the colours of things. One important aspect of the representational criterion is that we can misrepresent, i.e, that we can get the information wrong. The following is a good example of this (see link): the image is black and white, but we seem to represent the image as being coloured.
Another way in which we can try to understand the senses is by appeal to their phenomenal character. There is something it is like for one to have a sensorial experience and different senses give us different types of subjective experiences. For example, vision has a particular phenomenology and you can tell whether you are touching or seeing a set of cutlery. Moreover, you can also tell if two different experiences are of the same sensorial type; for instance, you can discriminate between seeing a red book cover and seeing a blue one and still know that both are cases of vision.
We can also individuate the senses by appeal to their proper sense organ and proximal stimulus. These two last two criteria are closely related. In the case of vision, for instance, the proper sense organ is the eye; vision is possible through the operation of this sense organ. Moreover, our eyes are receptive to a very specific physical thing; namely, vision’s proximal stimuli are the electromagnetic waves. Our retinas detect “electromagnetic waves in the range between 380 and 750 nanometers, the portion of the spectrum that we call visible and which corresponds to the colors between violet and red. We can’t see anything outside this spectrum, and we call the outside edges ultraviolet and infrared.” (Cervero, 2012, p. 40)
Let’s now apply these four criteria to pain:
First, what can we say about pain in terms of representation? One of the most discussed representational theories of pain proposes that pain represents bodily damage (see Tye 1996, 1997, 2006). In other words, having a pain experience can be understood as representing some type of damage happening to our bodies. If pain represents damage, can it also misrepresent as in the vision example? I think phantom limb pain could be a good candidate for this. In these cases, people feel pain in an amputated part of their body. They have an experience that misrepresents, e.g., it may represent their bodies as having a damaged hand, even if they have no hand.
We can also think of pain in terms of its phenomenology. There is a certain “what it is like for one” to undergo pain and we can identify pain as a having a distinct phenomenology. By appeal to this phenomenology, one could argue, we are capable of distinguishing pain from other senses as a distinct one; you can, for instance, tell if you are being cut or seeing a red surface. However, even if accept that pain can be generally be distinguished from vision, there are cases where the distinction is less obvious. For example, looking at extremely bright lights seems to be both visual and painful.
Let’s now consider the sense organ and proximal stimulus criteria as applied to pain. Medical research throughout the 20th century suggested nociceptors as a good candidate to be pain’s sense organ and noxious stimuli (i.e, stimuli that are damaging and harmful) as pain’s proximal stimulus:
Nociceptors are injury detectors. We now know that nociceptors exist all over the skin, in most internal organs, in muscles and joints, and in all other parts of our bodies from which we can experience pain after injury…There are basically two kinds of nociceptors: those that respond only to high-intensity mechanical stimulation and those that respond to several forms of high-intensity stimulation, including low and high temperature, high-intensity mechanical energy, and pain-producing chemicals. (Cervero, 2012, p. 42- 43)
However, (i) not all pains involve nocipceptors, such as neuropathic pain, (ii) not all nociception involves pain, since heat can activate our nociceptors without provoking pain, and (iii) not all noxius stimuli cause pain, like radiation which is damaging but not painful. However, I think, it is important to point out that nociceptors are often involved in acute pain experiences and noxious stimuli normally cause pain.
Can we then consider pain as another distinct sense? Following Macpherson, I think that once we’ve applied each of the traditional criteria to pain, we have said everything interesting that there is to say about pain as a distinct sense.
Cervero, F., (2012), Understanding pain : exploring the perception of pain, MIT Press.
Macpherson, F., (2011), “Individuating the sense”, in The senses : classic and contemporary philosophical perspectives / edited by Fiona Macpherson, Oxford University Press.
Tye, M. (1996). Ten Problems of Consciousness: A Representational Theory of the Phenomenal Mind. Cambridge, Massachusetts: MIT Press.
Tye, M. (1997). A Representational Theory of Pains and their Phenomenal Character. The Nature of Consciousness: Philosophical Debates. N. Block, O. Flanagan and G. Güzeldere, Eds. Cambridge, Massachusetts: MIT Press.
Tye, M. (2006). Another Look at Representationalism about Pain. Pain: New Essays on Its Nature and the Methodology of Its Study. M. Aydede, Ed. Cambridge: Mass.: MIT Press.