Do colours, sounds and odours as we experience them exist out there in the external world? I think so.

1. Introduction

Common sense holds that what has been labelled the secondary qualities, such as colours, sounds and odours, exist out there in the world independently of us. For example, grass really is green regardless of whether anyone is looking at it or not – that is, it is an objective feature of the world. In stark contrast, academics and the scientifically educated overwhelmingly reject this view. They hold that colours, sounds, odours and the other secondary qualities do not exist out there in the world at all, rather they only exist as an experience produced by the brain. This is in contrast to their position on the primary qualities, such as shape and size, which, like common sense, they regard as existing out there.

To explicate this academic view regarding the secondary qualities, let's consider the example of colours. Briefly, the story goes like this: objects reflect particular wavelengths of light, this light then enters the eyes and precipitates a chain of physical processes in the brain, finally, the brain somehow crafts the experience of a colour from these signals it receives. In this story, it should be stressed that the light itself is not considered to be coloured at all, the colour only comes into existence at the end of the causal chain. Watch this video for a simplified scientific story of what happens.

I find it hard to convey how utterly radical this conception of the world is. A world that is entirely bereft of any colours, sounds or odours is a deeply alien one, and arguably unimaginable. It is a bare skeletal outline of reality denuded of the flesh of the qualitative. Roses are not really red, violets are not really blue. And an unpleasant odour is not literally out there in the world, rather allegedly it's a fabrication created by our own brains! 

So given the radical nature of the claim, one would expect a lot of pushback. But, curiously, it seems almost entirely absent. Even those who typically believe in psi and an afterlife and constantly question mainstream academic positions, accept the arguments advanced for this conception of reality. Indeed, these very same people have, at times, been quite trenchant and dismissive of my own belief that the world is more or less as we perceive it to be. On this issue, I seem to be virtually a lone voice. So I thought I would set the record straight and explain why I remain intransigent on this matter.

Here's how I intend to proceed. The next part, part 2, will be devoted to advancing arguments for this thesis that the secondary qualities do not exist out there. Part 3 will be devoted to questioning these arguments with part 3(i) mostly addressing the perceptual illusion argument and part 3(ii) addressing the causal story argument. Part 4 will be devoted to articulating an alternative to this causal story. In Part 5 I will give my concluding thoughts.

Throughout this essay, I will largely be focussing on colours. However, it can be assumed that, in the main, similar arguments are equally applicable to the other secondary qualities. I will also, contrary to my own views, follow the standard practice of referring to the brain rather than the mind as playing a pivotal role in shaping the contents of our sensory perceptions.

2. The arguments for the claim that colours, sounds and smells as we experience them do not exist out there

To recapitulate, the commonsensical view is that colours, sounds, smells and the other secondary qualities exist out there, and we just passively perceive them as they are in themselves. But such a view is rejected by the vast majority of scientists and philosophers, and indeed has been labelled naïve realism. Why naïve? In the main, it's because perceptual illusions seemingly demonstrate that such a view is untenable.

Let's first of all consider illusions involving vision. The two most impressive ones I've ever encountered are the shadow-checker illusion and that famous dress. In the former, the squares A and B appear to have very different colours. However, if we remove most of the picture leaving just the squares A and B, then, much to our astonishment, we will see that they are actually the very same colour.

With the dress, it is either perceived as being white and gold, or alternatively as being black and blue. If that were not astonishing enough, the very same individual might initially see it as being coloured one way, but then at a later date are only able to see it as being coloured the other way. Indeed, this actually happened to me. Initially, I could only see the dress as being white and gold, but ever since that first day I can now only see it as being black and blue. It now seems baffling to me that I ever saw it as being white and gold!

 

Perceptual illusions also apply to our other senses. Take a look at this video that demonstrates that what we see can quite literally shape and change what we hear. And, contrary to what most of us might suppose, perceptual illusions even apply to what we smell and taste. For example, we might naïvely suppose that the taste of our food and drink won't literally be affected by its appearance. A tasteless colour additive will surely just make it look more pleasing to the eye. So any perceived difference in the taste of the food or drink might just be assumed to be imaginary. But, apparently, it does quite literally change the taste. A fact that should be borne in mind should anyone ever offer you apple juice in a clean bedpan! (3rd paragraph under the subheading "the power of disgust"). We should also bear in mind that smell is closely related to taste. Hence, since the appearance of food changes the taste, we can be confident it changes the smell too.

It is of vital importance to understand that perceptual illusions are not outliers in how we perceive the world. They are not tricks. Rather they underscore the way that we always sense the world. Indeed, everything we ever perceive could, in a sense, be considered to be an illusion. 
 

Let's illustrate this fact by considering vision. We typically see objects under a variety of different lighting conditions. Sometimes objects are in shadow, sometimes they're not. Sometimes we see objects in the sunlight, sometimes under artificial lighting. Even when we see an object outside on a cloudless day the lighting conditions constantly change. For example, when the Sun is low in the sky the sunlight has to travel through a greater quantity of air, which affects the lighting conditions.

 

These lighting conditions in turn play a role in determining which wavelengths of light are reflected off objects. But, in physics, colours are defined by wavelengths of light. Hence, since one and the same object frequently reflects differing wavelengths of light, we should expect a specific object to be constantly seeming to change its colour. Yet remarkably, under a wide variety of lighting conditions, specific objects more or less appear to be of the same colour. This phenomenon is referred to as colour constancy. For example, regardless of whether or not an object is in shadow, it looks more or less the same colour. And something like a rose will look more or less the same shade of red throughout the daylight hours, despite the different wavelengths of light being reflected off it as the day progresses.

We can infer then that we do not simply passively perceive what is out there. In the case of our vision, it's not as if we are looking out of a transparent window onto the external world just simply seeing what is out there. Rather, seeing is an active process. That is, the brain plays an active role in shaping the colours we see. What seems to be happening here is that the brain holds an unconscious implicit hypothesis about the nature of the external world. This hypothesis includes the idea that objects have intrinsic unchanging colours. So the brain adjusts accordingly, shaping and moulding visual experiences to try and ensure that specific objects appear to retain more or less the same colour irrespective of all the differing lighting conditions and the actual wavelengths of light entering our eyes.

Furthermore, consider also that our sensory experiences will not be the same for all individuals. For example, some individuals have varying degrees of colour blindness or colour vision deficiency. It also seems that animals differ from humans in what they can sense. Some see fewer colours than we humans do, but other animals, most notably many insects, see more colours. And animals also differ significantly in their other senses too.

So naïve realism does not seem to be tenable. The secondary qualities that we experience are not just determined by objective features of the world such as wavelengths of light, they are also influenced by a perceiver's expectations and beliefs, as well as, of course, the nature and structure of a perceiver's sensory organs and brain. But if what we perceptually experience differs from what the world is like in and of itself, then how do we know colours and the other secondary qualities exist out there at all? 

None of the foregoing in this section makes it conclusive that colours and the other secondary qualities do not exist out there. But the case is arguably considerably strengthened if we also take into account the alleged fact that we have a complete scientific story for how we perceive. Crucially, this story involves only the primary qualities as being causally efficacious – the secondary qualities are deemed to be causally impotent. So, in the case of vision, it is the wavelengths of light only, not the experienced colours associated with those wavelengths, that figure in the scientific story of how we perceive colour. And the same applies to the other secondary qualities.

I will now summarise the arguments that colours and other secondary qualities do not exist out there.

a) We do not passively perceive the world, rather the brain moulds and shapes our perceptions to make them congruent with our implicit expectations about what the world is like. Hence, a colour as perceived might be very different from the actual colour of objects. So why believe there are actual colours out there at all?
 

b) Secondly, two individuals can perceive a secondary quality very differently. Indeed, this is even the case with unimpaired senses since one's implicit expectations and beliefs play an important role in what we perceive. The dress is an excellent example that illustrates this since two individuals can see radically different colours. Indeed, even the same individual can perceive the dress as having very different colours on two separate occasions.

c) The alleged clinching argument is that we have a complete scientific story of how we perceive secondary qualities, and no reference is made to any actual secondary qualities existing out there in the world. Hence, even if they do exist, they play no role in explaining our experience of the secondary qualities.

 

3. The Pushback

(i). The argument from perceptual illusions dismantled

Let’s consider the shadow-checker illusion again. Suppose this was an actual object in front of us with the image on our retinas approximating to the 2D picture presented to us on our computer or mobile screens. Despite the wavelengths of light entering our eyes from squares A and B being identical, the way our vision works we will perceive squares A and B as having very different colours, just as in the 2D illusion. Yet we're not being fooled since if we were to approach this object, and view it from various perspectives, then we would effectively confirm that squares A and B are indeed very different colours and to the same degree as we perceive in the 2D illusion.

But what if we were to see reality as it supposedly really is with us experiencing the colours corresponding to the wavelengths of light entering our eyes? Then viewing the checkerboard 3D object from the perspective corresponding to the 2D picture, we would see squares A and B as being the same colour. The problem here is that, in reality, they are not the same colour! Moreover, perceiving them as the same colour will compromise our ability to recognise it as being a checkerboard at all. It is in consideration of these reasons that I have argued elsewhere that, properly speaking, the shadow-checker illusion shouldn't actually be considered an illusion at all. See here and here.

More generally, since differing lighting conditions influence the wavelengths of light reflected from objects, then if we were to simply experience the colours corresponding to the wavelengths of light entering our eyes, the colours of objects would appear to us to be in a constant state of change. In short, we wouldn't be seeing colours as they are in themselves out there in the world. And as with the checkerboard, it would compromise our ability to recognise objects.

If colours do exist out there in the world and objects are intrinsically coloured (they retain precisely the same colour over time), then their actual colours correlate poorly with the wavelengths of light that enter our eyes. The fact we do not see the colours corresponding to these wavelengths cannot therefore be used as an argument that we're not seeing the world as it is. On the contrary, the very fact that our brains mould and shape the colours we actually perceive by taking into account the lighting conditions, suggests that we do see the world with its colours more or less as it is in itself. Of course, it also entails that our vision is an active rather than a passive process. That is, the brain moulds and shapes and infers what the world is like. But that doesn't mean to say that what we eventually perceive, what the brain infers, cannot be normally a fairly accurate representation of what the world is like in and of itself.

 

It should be noted, though, that often this inference by the brain goes askew. The incorrect perception of the colours of the dress made by those who perceive it as being white and gold is one such example, although to be fair we are limited to viewing a 2D photograph of it, so it is easy for the brain to misinterpret the lighting conditions. Also, colour blindness or colour vision deficiency will clearly subvert our ability to correctly perceive colours. And even with unimpaired colour vision, we can only see a fraction of the colours that some other animals can. However, how is any of this more significant than the fact that some people have better visual acuity than others? Or that we can only see a fraction of what is out there in contrast to what we can see utilizing a telescope or microscope? No one suggests that from the fact our vision acuity is limited, or from the fact we have poor vision, that there is no world with a definite character out there at all!

 

The denial that the world has any secondary qualities from the consideration of perceptual illusions faces a further challenge. It is that the arguments presented in part 2 equally apply to some of the primary qualities, most notably the size and shape of objects. Consider that the perceived size of objects, just like colour, is also to a certain extent moulded and shaped by the brain. The moon, for example, looks larger near the horizon than it does when it is high up in the sky. Yet we would not generally claim that size is purely a fabrication produced by the human brain. That is, it is assumed that objects out there, such as the moon, have a real size independent of human perception. And the same applies to the shape of objects. Consider the Shepard tabletop illusion for example (I also talk about this illusion here). So just like colours and the other secondary qualities, the perceived size and shape of objects also vary depending on how the brain interprets the external world. Hence, to say that due to perceptual illusions colours, sounds and smells are not out there in the external world, yet size and shape are, seems to apply a double standard.

 

There's something else to consider, and it's arguably more important. Consider that the visual appearance of an object is distinguished from the background by its colours -- such colours essentially outline its shape. Hence, it seems incongruous to suggest the shape is out there but that its colour is somehow produced by the brain. Both the shape of an object and its colour both seem to be out there at a distance from us. Moreover, and even more importantly, they both come to us as a seemingly undifferentiated whole. Can we really subtract the colour of an object from its shape? It seems peculiar and implausible to me to imagine we can do so. Surely either both are out there, or neither are?

 

This sub-section has argued that perceptual illusions and what they imply about how we perceive, do not suffice, nor indeed even give any particular reason to doubt that colours exist out there. Similar arguments can be applied to the other secondary qualities. We now turn to the claim that only the primary qualities are required to exist to explain why we perceive the secondary qualities. 

 

 

(ii). The argument from the scientific story called into question

As previously mentioned, the scientific story goes like this. In the case of colours, objects reflect particular wavelengths of light, this light then enters the eyes and precipitates a chain of physical processes in the brain, finally, the brain somehow crafts the experience of a colour from these signals it receives. In this story, it is only the measurable aspects of reality that are deemed to have any causal efficacy. That is to say, it is purely these measurable aspects of reality that provide a full account of how we perceive both the primary and secondary qualities.

 

There is a problem here though, and it is this: we do not in fact have any such scientific story! For what we encounter here is the notorious hard problem of consciousness. The unreflective view is that consciousness is supposed to come into being as the end consequence of material chains of causes and effects. Such causes and effects are cashed out completely in the form of processes that we can measure; namely particles with physical properties such as charge, momentum, spin and so on. Each link in the chain of causality follows as a direct result of these properties. But, at the end of such causal chains terminating in the brain, we get a sudden abrupt change, a radical disconnect from these measurable processes to subjective experiences such as the greenness of grass, the warmth of love, the smell of roses and so on. These subjective experiences do not have physical properties, so we cannot, seemingly in principle, derive them from the prior physical causal chains. So the scientific story only takes us up to the end of the material chain or chains of causes and effects. We lack a causal story for how this final link in the causal chain – the activity in the brain – somehow creates, precipitates, or translates into a perceptual experience (or any other mental event). Indeed, this inability to specify a causal mechanism even rules out it being a scientific hypothesis least of all a scientific story. 

 

Reductive materialism attempts to negate this problem by holding that conscious experiences are either literally identical to certain brain processes, or alternatively, that conscious experiences are somehow entailed by brain processes, though there is a great deal of debate about the nature of such "entailment". But in the case of either identity or at least metaphysical entailment, this then meets the challenge of the last paragraph since under this assumption of materialism we now have a causal story of how we perceptually perceive.

Let's for the sake of argument, and contrary to my own view (see here and here), take for granted that a type of materialism so characterised is unproblematic. It nevertheless wouldn't be purely a scientific story of how we perceive since one would be assuming upfront the type of materialism so defined. A scientific justification for rejecting the existence of secondary qualities in the external world cannot be predicated on a certain metaphysical stance being true. That is, if we are to have a scientific justification for supposing that colours, sounds, smells and tastes are conjured up or created by the mind rather than residing in an external world, then this ought to apply under any metaphysical stance on the mind-body problem, even if it resembles something like Berkeley's immaterialism (more on immaterialism/idealism near the end).

 

However, let's for the time being waive this objection aside and see how the assumption of some suitable type of materialism fares in this causal story. With what justification do we hold that colours, sounds and smells are either identical or entailed by processes in the brain rather than being identical or entailed by the original causal triggers in the world, namely the wavelengths of light reflected off objects? For example, why can't, say, the redness we experience when looking at a strawberry be literally identical to the specific wavelength of light reflected off that strawberry under some ideal lighting condition? By this means, we could thereby conclude that colours, and the other secondary qualities, are actually out there in the world.

One response would be to point out that the role of the light wave ends when it initiates the chain of causation in one's brain. So the causal story implies that it is the last physical events in the brain that are somehow wholly responsible for our experience of colours, and indeed all other sensory experiences too (whether primary or secondary). This seems to suggest that the identity or entailment should reside in those last physical events. Hence, in a suitable sense, we might say a brain state is red, but a strawberry that one is perceiving is not literally red.

 

On the other hand, the fact that it is the final physical events in the brain that are supposed to be fully responsible for our perceptions, irrespective of whether they're primary or secondary qualities, appears to introduce a possible inconsistency. For it might be considered to be peculiar that our perception of shape and size, despite being immediately caused by brain processes, are nevertheless held to resemble the objects that are actually out there, whereas the perception of colour, odours and sounds allegedly do not. Can such a distinction be justified? One possible response is to point out that, unlike the secondary qualities, we have independent means whereby we can ascertain the shape and size of objects. For if objects are within reach, we are able to obtain a tactile confirmation of the shape and size of the object in question.

I agree that we can be confident in our supposition that shape and size are really out there. Yet this doesn't alter the fact that processes within the brain, which themselves are quite unlike shape or size, can nevertheless convey the visual experience of the correct shape and size of an object. This being so, why can't the same apply to the secondary qualities? Why can't processes within the brain, which themselves are quite unlike wavelengths of light, convey the experience of the correct wavelengths of light that reflect off the objects we perceive? And if colours are identical to, or metaphysically entailed, by specific wavelengths of light, we would then be effectively perceiving colours out there. And a similar point applies to the other secondary qualities. Of course, one might be tempted to point out that wavelengths of light are not colours! But this incredulity should be directed at materialism itself since it is surely no more plausible to declare colours and the other secondary qualities are identical to brain processes. I conclude that, even if we assume materialism is correct, under its logic we have no good reason to reject the idea that colours and the other secondary qualities, in a suitable sense, exist out in the external world itself. 

 

What of other positions apart from strict materialism, including those that still accept the brain somehow creates the mind? Since here the identification of conscious states with brain processes is being rejected then we no longer have a causal story accounting for how we perceive anything at all. Yes, we can trace the causal story from the light reflecting off an object to the physical activity at the end of the causal chain in the brain, but we are completely lacking an account of how this elicits, or translates, into a specific perceptual experience. This is regardless of whether we have in mind the secondary or primary qualities.

 

The fact is, though, that we do nevertheless have sensory experiences and, furthermore, we are here assuming that it is the physical processes in the brain that somehow creates these experiences. So we might be tempted to ask again that if our experience of the shape and size of an object somehow, by some unknown means, corresponds to that which is actually out there, then why not our experience of colours and the other secondary qualities? The answer that many will give is that something like colour can't reside in external objects as it doesn't have any causal powers, only the wavelengths of light do. So, since, unlike materialism, we're not identifying colours with wavelengths of light, nor with anything else that has causal powers, then colours cannot exist out there.

This, though, seems to me to be susceptible to the charge of subtracting the causal power of a thing from the thing itself. The waves on an ocean comprise much of the causal power of that ocean. But obviously, the body of water constituting the ocean exists, and indeed the waves are simply a property of that water. Likewise, it might be that something like the red we experience exists out there, and it has the property associated with a specific wavelength of light with this property being a manifestation of its causal power.

 

I conclude that, in addition to the argument from perceptual illusions, the alleged scientific story also fails to rule out the existence of secondary qualities existing out there in the world.

4. Are we obligated to accept the Causal Story?

As I have argued, this causal story cannot be regarded as a scientific one. This being so, why should we be obligated to accept it? Let's face it, it is wholly contrary to what seems to be the case. When we see, hear, smell, touch, and taste, it seems that we are in direct contact with the external world, that we see it in a direct sense. Yet we are being asked, instead, to believe that the processes occurring inside our skulls are the proximate cause of everything we ever perceptually experience, indeed the cause of the entirety of our conscious lives. This also has the consequence that we could, at least in principle, all be brains in a VAT (similar to within the film, The Matrix). Certainly, at the minimum, if we accept academics' belief that the secondary qualities do not exist in any manner within the external world, this means our senses are at least being partially deceived about what the external world is really like.

This is all deeply implausible. So we need compelling reasons to accept this story. Yet it seems to me that we lack any such compelling reasons. Indeed, I question whether we have any reasons at all. But are there any reasonable alternatives? My response is an emphatic yes. Let's see how.

In part 3(ii) I mentioned two possibilities that can be squared with this causal story; namely either a type of reductive materialism, or alternatively just accepting as a brute fact that where there are appropriate neurons firing, an experience will simply spontaneously occur. But even if we were to grant these positions are intelligible, why believe in either of them? Why believe that brain activity creates our perceptual experiences in the first place? 

This last question might elicit exasperation in some readers who might well be thinking that of course brain activity causes or creates our sensory perceptions! That we know this since disruption of particular brain activity adversely affects such perceptions. However, I am not disputing that relevant brain activity needs to occur in order for people to perceive. Compare this to the fact that having our eyes open is necessary to see. Yet having our eyes open doesn't play a causal role in creating our perceptual vision, rather it simply allows perception to take place. Likewise, although it is acknowledged that the physical causal chain of events from the light entering one's eyes until the final activity in the brain, is required to take place before we are able to perceive, we can deny that the final brain state, or indeed any of the preceding causal chain, causes or creates our perceptions.

Note that I am not claiming that the mind or brain cannot conjure up what might seem like perceptual experiences. Clearly it can, as exemplified by dreams and hallucinations. But, in the case of perceiving the external world, I suggest the brain does not proximately create what we perceive, though it does change, mould and shape those perceptual experiences.

Now, if neither brain activity nor any of the other processes along the causal chain cause our perceptual experiences, this seems to suggest that the commonsensical conception of how we perceive might be true after all. In other words, when we perceive something we are in direct contact or directly perceive that object. How, though, does the direct perception of the external world work? For although the causal chain is necessary in order for perception to take place, it nevertheless is not the medium whereby our perceptions are caused.

Perhaps to some people's consternation, it does not seem to me to be problematic to simply suppose that the capacity to perceive is innate to the self or soul. The role of the sensory organs and brain would then be to merely change, modulate, and attenuate our perceptions (this is similar to my belief regarding all of our conscious states. See part 5 of this blog post of mine where I go into more detail). I should add, though, that this hypothesis need not entail that a disembodied existence is possible. The capacity to perceive might be innate, but with our minds nevertheless dependent on a body. 

It should be clarified that in claiming we directly see the external world, this is not to claim that we are seeing external objects exactly as they are in and of themselves. For one thing, the acuity of our vision and the other senses will vary from individual to individual and from one species to the next. For another, as I said earlier, our brains mould and shape our perceptual experiences. But our brains – or, as I prefer, our minds – can be directly presented with the external world, and yet interpret what is actually being experienced. In either case, our perceptions will be direct providing the object itself is the immediate cause of our perception rather than any intermediary or intermediaries along the causal chain playing that role.

Even if one finds this commonsensical hypothesis unconvincing there are other philosophical perspectives that reject the mainstream belief. There is Berkeley's immaterialism (otherwise known as subjective idealism), as well as other types of metaphysical idealism. In addition, there is hylomorphism, occasionalism, psychophysical parallelism, and others, all of which have colours, sounds, and odours populating this external world just as much as the primary qualities do. Of course, it might be objected that many of these metaphysical positions, such as immaterialism, are fanciful and implausible. However, given the extremely implausible nature of the mainstream position, it is not clear to me that this is a decisive objection.

Note that if science had shown that the secondary qualities are fabrications conjured up by the brain and represent nothing out there, then it follows that science would have refuted these metaphysical positions. But informed people do not generally hold this. People might, for example, emphatically reject Berkeley's metaphysic, but not due to this reason.

5. Concluding Remarks

It is an extraordinary claim to suppose the external world is wholly devoid of any colours, sounds or odours, and that it is our brains that somehow fabricates these experiences. So we need very compelling reasons to suppose it is true. Yet it seems to me that not only do we lack any such compelling reasons, it's difficult to find any reasons at all! Even a more or less commonsensical conception of how we perceive doesn't appear to be overly problematic, although, admittedly, naïve realism is not, strictly speaking, tenable. Certainly, there doesn't seem to be any reasons for doubting the secondary qualities exist out there for any metaphysic resembling idealism, or any other position that holds that we perceive directly. Furthermore, even if we subscribe to the causal story of how we perceive, and even subscribe to a type of reductive materialism, it is not at all clear why the external world has to lack secondary qualities.

Personally, I think this rejection of the secondary qualities existing out there originates from a conviction that only the quantifiable or measurable aspects of reality exist. After all, this is all that science requires in order to work, and science has been stunningly successful over the past 350 years or so. Of course, the problem here is the existence of conscious experiences, which appear to involve more than mere measurements. Nevertheless, by denying that colours, sounds and odours exist out there in the external world and relegating them as being mere fabrications created by the brain, this at least means that it is only consciousness that is an anomaly, the rest of the material Universe then can be wholly explained by our physics. So somehow consciousness has got to be explained away. Hence, the attraction of deeming consciousnes as being literally identical to brain processes, or even that it doesn't literally exist at all! But all such options seem to me to be both desperate and transparently false. I cover the issues addressed in this paragraph in more detail here. 

What I find significant and very interesting is the complete conviction amongst virtually everyone, including those who subscribe to an afterlife, that the colours, sounds, and smells we sense in the world are not in fact out there at all but are a fabrication created by our brains or minds. This is a truly radical belief that is totally at odds with common-sense, and, as I hope I have demonstrated, contrary to reason too.