Naive realism is a widely debated topic in the philosophy of the mind. In this article I will review the theses of naive realism through the works of one of the most influential philosophers who supported and developed them, Michael Martin. Once the reasons why naive realism should be supported are discussed, I will propose an empirical argument to show that naive realism and the most basic scientific knowledge of perceptive processes are contradictory.
Naive realism is a philosophical position at the center of the debate on perception in philosophy of the mind. Thanks to the importance of studies on perception, naive realism has attracted the interests not only of philosophers of the mind but also of students of semantics, epistemology and of those who deal with determining the nature of phenomenal consciousness. For naive realism, the metaphysical structure of conscious perceptual experience cannot help but involve material objects independent of the mind.
The philosophical position that currently opposes this way of seeing things is called representationalism. Those who hold the representationalism view believe that perception has the characteristic of being an intentional activity. The perceiving subject is intentionally linked to a representational content. When we perceive we see the world being in a certain way. As an example, we perceive that “A is red”.
If we see an object X as Y, this is our view of the world around us. Such content can be real or not. If real, we are dealing with a genuine perception. Otherwise, it is an illusion or a hallucination. Usually those who embrace representationalism contend that naive realism supporters fail to explain phenomena such as hallucinations and illusions.
In this article I will review the theses of naive realism through the works of one of the most influential philosophers who supported and developed them, Michael Martin. Once we have understood the reasons why Martin believes that naive realism should be supported, I will put forward an empirical argument to demonstrate how naive realism contradicts the most basic scientific knowledge of perceptual processes.
The naive realism of Michael Martin
In The Transparency of Experience, Martin addresses the problem of how naive realism can account for illusive and hallucinatory experiences. Martin points out that illusions, hallucinations and perceptions can be considered totally different experiences. There is nothing strange in saying that perceiving means being in relation with objects of the world that surrounds us independent of the mind whereas, in cases of hallucination and illusion, our experience is something substantially different. Not even the fact that both illusions and hallucinations lead us to believe that we are experiencing events in the world around us should make us conclude that they must have something substantial in common with perceptions. In other words, it is not enough that illusions, hallucinations and perceptions are subjectively indistinguishable to conclude that they should have some ingredients in common.
After The Transparency of Experience, the heart of naive realism was spelled out by Martin in the article The limits of self-awareness:
«The Naïve Realist thinks that some of our sensory episodes are presentations of an experience-independent reality. I am aware of the various elements that make up at North London street scene. The same objects and aspects of these objects which I can expect to be when I pursue the question, rather than writing my paper?» 
In this second article, Martin carries forward and elaborates the arguments previously seen, considering the case of illusions no longer problematic. Martin argues that the broadest way to account for any perceptive experience is to consider everything in that experience which cannot be distinguished from careful reflection of veridical perceptions. In other words, characterizing hallucinations negatively is for Martin the only way to account for hallucinations and perceptions as perceptual experiences.
If hallucinations had their specific mental properties, they could be identified through careful reflection, but this does not happen. We may have the necessary conditions to determine if it is a hallucination only if we have the ability to discriminate mental properties of hallucinations when they are present and to identify their absence when they are not.
Martin argues that there is a limit which awareness cannot go beyond. Precisely, this limit is the impossibility to distinguish between hallucinations and veridical perceptions. The existence of this limit is difficult to contest. But if this limit exists for Martin, then representationalism must be false.
«If one cannot tell what it really takes for experience to be one way rather than another, why should we think that one can still always tell that some mental presentation or other must be responsible for things to seem the way that they are? So the epistemological commitments of Common Kind view seem to be in tension with the reasons for accepting them.» 
In On Being Alienated Martin seeks further to shelter naive realism from skeptical Cartesian and Humean arguments. These arguments are taken as exemplary cases which give rise to the debate over naive realism and how to account for hallucinatory experiences with respect to veridical perception. To the skeptical Cartesian question, “How do I know that what I’m perceiving is reality and not a mere dream or the work of an evil genius?” Martin replies that this can simply be answered that “I know because I’m really perceiving something”. In other words, to raise a doubt there must be sufficient reasons for this doubt to make sense. If I perceive objects in the world around me daily and if there are no internal motivations to my experience to make me suspect it is not genuine, then it makes no sense to raise a doubt like the Cartesian about the veracity of such experiences.
«Before the sceptical challenge is raised, it seems as if there is a simple answer to the question, how do you know that there is a white picket fence there? After all, you can simply see that there is one there, and that you can see that one is there is something that you also have access to.» 
As for Humean skepticism, Martin believes that it is reflected, in our day, by the famous “hallucination argument” and its assumption that hallucinations and veridical perceptions are. For Martin it can be denied that hallucinations and perceptions must be of the same kind. In fact, it can be argued that on the one hand perceiving means entering in contact with objects of the world around us.
On the other hand, hallucinations are something that deceives us in two different ways. Not only does seem in the hallucination that there are objects in the environment that surrounds us, which in fact are not there, but we even believe we are interacting with those objects, which is equally false. Given this double deception it is illegitimate to think, according to Martin, that because in hallucinatory cases we are deceived about what we are seeing, then we should think we are also in cases of veridical perception.
In What’s in a look? Martin focuses his attention on propositions that indicate the vision of something like “that dog is brown”, “that cat looks sleepy” or other propositions of this kind. Some of these propositions do nothing but bring our visual experience back while others have a subjective nature for how they are used. For Martin in our talk of appearances and sensory states, as when we say that “an object X seems Y”, we make a comparison between objects in which we decide whether an object has a visible quality exactly as it is possessed by another object.
When we talk about visual propositions, according to Martin, we do nothing but talk about the visible qualities possessed by objects and from the semantic point of view there is not much else to analyze. Representational theory like the other theories advanced over the years are all consistent with this analysis of the propositions about visible qualities. But that means there’s nothing in our way to report visible qualities that can be used to decide which of the multiple options is the best to account for the metaphysics of perception.
In fact, Martin writes:
«The minimal semantics I have offered is quite consistent with a representational or intentional theory of sense experience and equally with a sense-datum approach. Nor have I said anything that compromises naive realism. The aim here has not been to favour one such account over any other, but rather to indicate reasons for why we should not look for evidence in favour of one of these views over the any of the others in the ways in which we talk of appearances.» 
The results achieved by Martin in the course of his defense of naive realism in the four articles briefly examined can be summarized as follows: (1) There is nothing in our way of talking about what we see that can make us conclude in favor of one or the other philosophical position on the structure of perceptual experience. (2) There is nothing in our way of perceiving reality that should make us think that what we perceive are not material objects of the environment that surrounds us, independent of our mind. (3) Hallucinations can be characterized in such a way as to deny that they must be of the same kind as the usual perceptive experiences. It can therefore be affirmed that (4) perceiving means entering into contact with objects of the world that surrounds us independent of the mind of the perceiving subject.
The naive realism is therefore a philosophical position on the metaphysical nature of perception if not correct, at least sustainable.
The naive realism and the scientific vision of sensory perception
The global function of the eye is to correctly project the light coming from the objects of the world around us on the retina. The light enters from the cornea that focuses the pattern of light along with the other lenses of the eye on the retina. The variable dilatation of the pupil helps to regulate the amount of incoming light and the shape of eye lenses, excluding the cornea, varies as the distance of the objects being observed varies.
The retina transforms the pattern of light into nerve signals conducted by the optic nerve. It allows us to discriminate the wavelengths and therefore colors. It consists of three sections of nerve cells, one occupied by cell bodies and the other by synapses formed by axons and dendrites of the same cells. The most numerous cells, the rods, are used for night vision and are ultra-sensitive to the light present, being able to discriminate even a single photon. The cones on the other hand are responsible for the discrimination of details and colors. The area of the retina most densely packed with cones is the fovea which is also the area with the most discriminative power.
The nerve signal that starts from the cells of the retina after being excited by the light travels up to the visual areas of the cerebral cortex where the signal coming from the retina is processed and processed. Now, what is processed by the retina is not the observed object that belongs to the environment that surrounds us but the light reflected by the object. Even if the light brought with it all the necessary information on the object, light and object would remain two distinct things.
The important point here is not exactly what we see. The point is that we can neither say that we are directly seeing either the objects of the world around us nor the pattern of light reflected by them. This leads us to deny point (4) of Martin’s arguments and, if it turns out that hallucinations are phenomena of the visual cortical areas of the central nervous system, that point (3) is also very doubtful. If the scientific narrative of perception is correct, then naive realism must be set aside and the relative metaphysics of perceptual processes must be rethought.
The functioning of the visual apparatus as summarized above tells us that it is incorrect to assume that what we experience on a daily basis are directly the material objects of the environment around us. This contradicts the fundamental assumption of naive realism. Martin’s arguments, although valid from a metaphysical point of view, clash irretrievably with what seems to be the scientific studies concerning human vision.
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