The next series of posts considers the human ability of perception and whether this can be considered a reliable provider of knowledge. This gives rise to two related questions: (1) what exactly is perception, and (2) is perception capable of producing reliable knowledge?
In regards to the first question, the main theories to consider are naïve realism, sense datum, intentionalism, and disjunctivist. Each of these will be considered in turn.
The main challenge for theories of perception is how to deal with hallucinations, illusions and other imaginary states, where the objects of perception are not real, or are real, but are experienced in a non-real state (such as seeing a straight stick as bent when viewed in water). For the subject, there may be no perceivable difference between a real experience and a hallucination, however we would not want to accept the hallucination as providing real knowledge. Each theory tries to find some way to distinguish hallucinations from real events.
Under this theory, objects exist independently of human perception, so any perception event creates a direct link between the object and the perceiver. Perception is therefore a process that creates a relationship between object and perceiver. The experience is not just a representation of something, it is an actual link to an object in the mind-independent world.
However, one of the main problems of naïve realism is deciding how we make a distinction between real experiences and illusions / hallucinations. Given that many false images can be very realistic, how do we limit perception to those experiences that involve real objects only? For the perceiver, there may be little difference between a real event and a hallucinatory one. In the case of illusions, one response is to claim that the illusion actually exists in the world itself, that is, it is the end result of a number of physical properties (eg, the amount of light, angle of reflection). The illusion itself therefore becomes a property of the object.
However, in terms of hallucinations, this becomes more difficult to explain, as there may be no real object in which to begin with. One might think that because the brain state of a real experience is identical to that of a hallucination, we might not need to draw a distinction between the two. However, the naïve realist will attempt to explain the difference in terms of a causal link. With the real experience, the perception was the direct result of having encountered the object. However, with the hallucination, this was not the case. The hallucination still occurred even though the actual objects were not present.
Another approach for the naïve realist is to accept more of a disjunctivist theory, looking at real experiences and hallucinations as having different natures. This is explained in more detail below.
Another puzzle for the naïve realist is explaining how two or more people can have different experiences from the same real world object, such as two people who perceive the same wall as having a different colour. If we are saying that a perceptual experience creates a link to the real world, shouldn’t this link be the same for everyone? There is no definitive response here by naïve realists, however some will explain the difference in the fact that no two perceivers can ever experience an event in the precise same way. For instance, the time may differ, or the amount of light varies, or the angle of perception might differ. Everyone has a unique standpoint where experiencing the same event.
This theory rejects the view that he have direct links to ordinary objects when we perceive something. Rather, all we have is a ‘mental image’ in our minds, which may or may not be related to a real object in the external world. If you see a red flower, the sense datum of ‘redness’ appears in your mind, and this is what you can be said to perceive. Conversely, if you think you see a red flower (when in fact the flower is white), you are still experiencing the same sense datum of ‘redness’. A sense datum theorist cannot draw a distinction between real experiences and imaginary ones. They are all still experiences of a sensory nature.
Therefore under the sense datum theory we do not have a direct link to real objects. The link is indirect at best (an idealist would argue that even this isn’t true – we have no understanding of the external world at all). The sense datum theory accepts that perception involves a relationship to objects, but it rejects the idea that these objects are real. Rather, we have access to a set of objects that are always available to us.
The main criticism of the sense datum approach is that it would seem to make objective, scientific knowledge (‘naturalism’) impossible. If sense datum is all we have, and these experiences do not give us any evidence of whether objects are real or not, then it would be impossible to make any objective claims about the world. The sense datum theorist cannot say whether the objects of perception are real or not.
An intentional theory holds that an experience is a particular mental state that represents something in the real world. In other words, an experience is a kind of belief. However the belief on its own does not create a relation between the mind and an object. This opens the possibility that the mind’s representation does not exactly match the object in the real world, so it is possibly for the mind to experience property X while the real world object has property Y. An intentional experience does not provide any evidence of an object’s reality.
However, the question then arises how the intentional theorist draws a distinction between a real experience and a hallucination. If they are claiming that the experience is all that matters, it appears we have no way of distinguishing a hallucination from an actual event. The intentional theorist would in fact argue that the hallucination is still a valid provider of knowledge, as it represents some aspect of the real world. In other words, the real world still has a part to play in creating representations. So while there may be no direct relationship – along with the fact that the representation might be inaccurate – the intentionalist accepts that a mind-independent world does exist and helps to shape experience.
A critic would respond here that if an intentional theory cannot help us to separate a hallucination from a veridical experience, then the theory cannot help us to obtain knowledge. Another line of criticism is that the intentionalist does not do enough to separate an experience from a mere thought. A person can think of any object they choose (a red flower), but this does not mean that the object is actually present. The critic argues that the intentionalist does not explain the special ‘feel’ we have when undergo an experience, which is different to just thinking about an object.
This theory can be seen as a reworking of naïve realism, in that it attempts to reconcile real experiences with hallucinatory ones (as explained in naïve realism above, illusions are less of a problem). A disjunctivist accepts that it is possible to have multiple types of perceiving experiences: one involving real and ordinary objects, and the other involving hallucinations. Furthermore, the experience itself might be identical, and impossible to tell apart. However, in terms of knowledge, we must draw a distinction between the two and only accept perception when real and ordinary objects are involved. The disjunctivist philosopher accepts that even though real experiences and hallucinations often appear to us in the same way, each has a different nature, so we must recognise that nature when assessing an experience.