Perception as a source of knowledge

AQA Philosophy

Direct realism

Direct realism is the common sense intuitive view that the objects of perception are physical objects which exist independently of our minds. We think of Physical objects as existing objectively in space and time. If I am in a room and perceive some physical objects in it, then when I leave the room they remain as they are unless they are undergoing some sort of physical process like burning which would cause them to change when I wasn’t there to perceive them.

Direct realism claims that our senses perceive those physical objects and their properties. For example, when perceiving the physical object of table, I perceive it’s properties such as color, shape, size, smell and texture.

The perceptual variation issue for direct realism

Bertrand Russell argued that what we perceive is not the same as what is in reality and so direct realism is false. Russell points to the example of a shiny, brown table. He argues that the color of the table actually depends on where you stand in relation to it. There is light falling on the table making a part of it shiny and therefore white in color in a certain spot, but if another person were to stand at a different place to you, that white spot would appear to them to be on a different part of the table than where it appears to you. Therefore, where one person sees the table to be white, another might see it to be brown. A particular spot on an object cannot be two colours at once, therefore colour cannot be a property of the table.

Russell argues this can apply to texture too. While the table feels smooth, on a macroscopic level it has indentations and grooves. Shape is also perceptually variable since it depends on the angle at which you view the table as to whether it looks square or rectangular.

Integration: direct realism is false in its claim that the properties we perceive are properties of a mind-independent object. Our perceptions must be mind-dependent sense data instead of direct perception of mind-independent objects.

P1. Our perception of an object can vary without any corresponding change in the object.
C1. Therefore, there is a difference between the properties that physical objects appear to have and the properties they really have.
C2. Therefore, what we perceive and what exists mind-independently are different.
C2. Therefore, the immediate objects of perception and their properties are different to what exists mind-independently.
C3. Therefore, direct realism is false.

Direct realists can respond by arguing that perceptual variation is the result of perceiving relational properties of mind-independent physical objects.

There are two types of relational properties:

  1. Relational properties between objects: properties that objects have in virtue of their relation to other objects. E.g.: being “hotter than” is a relational property the Sun has to the earth.
  2. Perceptual perceptual relational properties: properties that objects have due to to being perceived. E.g.: The property of “looking square” or “looking rectangular”

It is the second type of relational property that explains perceptual variation. Since the relation of an object to a perceiver can change, so too can the perceptual relational properties that the object has.

Integration: this response from direct realists denies the inference from P1 to C1. Perceptual relational properties are directly percieved properties of an object, but it only has them through being percieved. So, our perceptions can involve relational properties that can vary without a corresponding change in the physical object (P1 is correct). Yet, this does not show that there is a difference between the properties an object really has verses appears to have (the inference to C1 does not follow). An object could have the relational property of ‘looking rectangular’ while also having the intrinsic property of ‘being square’.

Indirect realists can attempt to respond. These perceptual relational properties are mind-dependent. Without a mind perceiving them, they would not exist. So, relational properties are dependent on minds. So, contra direct realism, when perceiving relational properties we cannot be perceiving properties “of” mind-independent objects or properties that they “have”. Relational properties are properties which an object is only perceived to have, not properties intrinsic to the object.

Integration: such properties must be of sense data; mind-dependent representations, rather than direct perceptions. It follows that in cases of perceptual variation, a direct realist cannot claim that they are perceiving mind-independent objects and “their” properties. So, direct realism is false.

However, direct realists can respond that there are two ways a perceptual relational property can be mind-dependent:

  1. Mind dependent due to being a property of sense data.
  2. Mind dependent due to requiring a mind to exist.

Indirect realists are trying to argue that relational properties are mind-dependent in the first way. Yet, direct realists can respond that they are only mind-dependent in the second way and that this second way does not conflict with direct realism.

The direct realist claims that the objects of perception are mind-independent objects and their properties. We perceive properties of mind-independent objects.  Perceptual relational properties may depend on minds, but nonetheless they are still properties that objects have due to their relation to a perceiver. They cannot only be properties of sense-data, since they do require an objective relation to an object. It is only from a particular angle that a square object could have the relational property of ‘looking rectangular’. So, indirect realists cannot say that the relational properties are mind-dependent in the way of being a property of sense data, i.e., exist only in the mind. It seems they actually belong to the objective relation between a subjective mind and an objective object.

Although perceptual relational properties are not intrinsic to an object, they are intrinsic to the relation between the object and a perceiver. They are mind-dependent, since the perceiver is essential to the existence of the property, but equally, so is the object. It isn’t correct to suggest that such properties only belong to the perceiver, i.e., only in the mind. They involve something objective about the relation between an object and a perceiver. Ultimately, it seems that perceptual relational properties belong both to an object and its perceiver. They involve an objective relation between a subjective mind and an objective object.

Integration: so, direct realism can be defended in its claim that perceptual variation can be explained through perceptual relational properties that are properties of mind-dependent objects. A mind-independent object can have relational properties that depend on a mind to exist.

The illusion issue for direct realism

If you look at a straight stick submerged in a glass of water, the light-refracting properties of water make it look bent. An illusion occurs when an object (the stick) appears to have a property (of bentness) yet in reality it does not have that property (It isn’t bent). Therefore, the perceived illusory property is sense data which exists in the mind, not reality. Illusions appear just as real as normal veridical perceptions – they are subjectively indistinguishable. Therefore, normal perceptions must also be of sense data in the mind, not of physical objects. So direct realism is false.

P1. During an illusion, I observe an object p with property y.
P2. According to direct realism, if I perceive property y, then property y exists mind-independently.
P3. During an illusion, there is no property y.
C1. Therefore, our perception of the property y of object p must be mind-dependent sense data.
P4. Illusions can be subjectively indistinguishable from veridical perceptions.
C2. Therefore, in all cases, the objects of perception and their properties are mind-dependent sense data.
C3. Therefore, direct realism is false.

The direct realist could respond by appealing to relational properties. A relational property is one that a thing has by virtue of its relation to something else. The stick could have the relational property of looking bent to a certain observer under certain conditions (such as being observed through water). This is a (relational) property that the stick has. So, observing a stick bent in water does involve observing a mind-independent object and its properties and therefore direct realism is not shown to be false by illusions.

The hallucination issue for direct realism

Hallucination occurs when perceiving an object that doesn’t exist. Therefore, what we perceived must be mind-dependent sense data. Hallucinations are subjectively indistinguishable from normal veridical perceptions, therefore normal perceptions must also be of sense data, not mind-independent physical objects. So direct realism is false.

P1. During a hallucination I observe an object p.
P2. According to direct realism, if I perceive object p, then object p exists mind-independently.
P3. During a hallucination there is no physical object p.
C1. Therefore, the object of perception p must be mind-dependent sense data.
P4. Hallucinations can be subjectively indistinguishable from veridical perception.
C2. Therefore, in all cases, the objects of perception are mind-dependent sense data.
C3. Therefore, direct realism is false.

Direct realists can respond with the disjunctive theory of perception. A disjunction is when there are two possible ways something can be. It is either one or the other. Hallucination is very different from normal veridical perception as it involves a mind separated from reality. Therefore this case is disjunctive as it must be either/or – it cannot be both – the mind is either connected to reality or separated. So, what we perceive is either a hallucination from our imagination or a veridical perception of reality. Just because those two possibilities appear the same, it doesn’t mean they are the same. In fact, since they are disjunctive, they cannot be the same. Therefore, just because hallucinatory cases are of mind-dependent sense data, it doesn’t follow that all perceptions are mind-dependent sense data too.

Integration: The disjunctive theory of perception shows the possibility that that when hallucinating we are experiencing the product of our imagination. We experience object p but there is no object p. Direct realists can thereby deny P1 and P2, that when we perceive an object p that there is something that is p.

The time-lag argument against direct realism

It takes time for light to reach us from an object we perceive. The light from the stars we see in the sky may have taken billions of years to reach earth. So we see those stars as they were billions of years ago, not as they are now. Although the objects of perception we more regularly see are much closer, like a table or chair, the light still takes some time to reach us. Therefore, we are not seeing the objects of perception directly, we are seeing them as they were in the past. Therefore, direct realism is false.

Indirect Realism

Indirect realism is the view that the objects of perception are a mind-dependent representation which is caused by external mind-independent physical objects. Sense-data is perceived immediately (directly) whereas physical objects are perceived indirectly. The representation can be different from the object it represents. The argument from perceptual variation, illusion and hallucination, which try to show that what we see isn’t necessarily the reality, argue for indirect realism

Russell defines sense-data as the ‘content’ of our immediate sensory perception.

John Locke’s primary/secondary quality distinction

Locke claims that the objects of perception have primary qualities which are ‘intrinsic’ to the object and secondary qualities which are just in our mind. Primary qualities are shape, extension, number, movement. Secondary qualities are colour, taste, smell, touch.

Locke argues for this distinction by pointing to the case of a grain of wheat. If you continually divide a grain of wheat, eventually it will become insensible, having no colour, taste, smell or touch. However, it will still have a shape, extension, number or movement. This shows that secondary qualities are separable from an object, whereas primary qualities are not.

Indirect Realism issue: Scepticism about the existence of mind-independent objects

Indirect realism claims that the objects of perception are mind-dependent sense data that represents and is caused by mind-independent objects.

However, if all we perceive directly are sense-data, then we never perceive the mind-independent objects which Indirect realists claim are giving rise to and being represented by that sense-data.

There is a ‘veil of perception’ between our sense data and the external world through which we cannot perceive. In that case, it seems we can’t actually know that mind-independent objects exist at all, let alone whether sense data represents them.

For example, solipsism could be true; that only my mind exists and my perceptual experience is caused by my imagination.

Integration: The first claim of indirect realism, that the objects of perception are mind-dependent sense data, undermines our ability to justifiably know the second claim, that sense data is caused by and represents mind-independent objects. So, direct realism is epistemologically self-defeating and we can never be justified in believing it.

Russell’s best hypothesis response to the issue of scepticism

Russell argued we can neither prove nor disprove either the claim that the external world exists and causes my sense data, or the claim that the external world does not exist and so does not cause my sense data. Since we cannot prove for certain either claim, we are left with making a hypothesis (a theory which is confirmed or disconfirmed by experience or reason). Russell argues the question then becomes which possibility – that the external world exists or does not – is the best hypothesis.

Russell points to the example of a cat. When first you glance, it is in a corner of the room. The next time you look, it is on a sofa. If there is no external world, then the cat just disappeared from one place in perceptual experience and then appeared in another. However that does not provide an explanation of the experience as there is no reason why that should happen. If we take the other hypothesis, that there is an external world so the cat is a mind-independent object which continues existing when unperceived, then we have an explanation of our sense data of the cat having moved to the sofa – it walked there when you weren’t looking! Since this hypothesis actually explains our experience, it is the better explanation and so, Russell concludes it is the best hypothesis.

However, Russell’s argument can be responded to. Why is the cat having its own mind-independent existence really a ‘better’ explanation of our experience? What criteria is Russell using to judge that? It makes more sense ‘to us’, but that could just be because of our habit of thinking that there is an external world. If we discount that, it’s hard to see what possible reason we could have to prefer Russell’s explanation to the explanation of solipsism – the view that only our mind exists and the physical world does not. Both explanations are equally consistent with any and all experience, therefore there is no justification to prefer either and thus no way to say which explanation is better, so Russell’s ‘best hypothesis’ argument fails.

John Locke’s argument from the involuntary nature of our experience

Locke argues that perceptions from sense experience have a key difference to perceptions from memory or imagination in that we have no choice over what we perceive in sense-data. However, we can choose what to remember or imagine. If there really were no external world causing our sense-data, then everything must be in our mind. In that case, we should expect to have choice over perceptions from sense experience. However we do not – if we look at a bottle of water we have no choice but to see one. Yet if we want to imagine a bottle of water filled with gold or remember the last time we drank from one, we can. Since we have choice over perceptions which originate from our mind yet we have no choice from those from sense experience, it follows that perceptions from sense experience do not originate from our mind but from an external world.

The argument from the coherence of various kinds of experience (Locke & Cockburne)

Locke also argues that sense-data from different senses back each other up. E.g if I see an apple, I can touch it to see if it also feels like one, and taste it to see if it also tastes like one.

Locke combines these two arguments in the example of changing how paper looks by writing on it – so sight and the sense of your hand moving cohere. You cannot cause the words to appear on the paper by mere imagination, you have to actually write. Once it is written, it cannot be changed except by further writing. If someone else read out what you had written, there would be coherence between your auditory (hearing) sense-data and what you thought to write. Lock argues this ‘leaves little reason for doubt’ that there is an external world.

Catherine Cockburn also responds to scepticism about the existence of mind-independent objects with an argument from experiential coherence. She first points to the radical difference between experiences gained from different senses. E.g. The sound a waterfall makes is not just different to but of a very different sort than the visual experience of it. Cockburn then points out we learn to pair visual and auditory experiences together such that we are able to make an inference from one to the other. If we are walking on a mountain and hear a waterfall, we can infer and accurately predict what it looks like; and vice versa, if we see a waterfall from far away, we can infer and accurately predict what it will sound like when we have moved closer. The fact that we can accurately infer and predict our experiences suggests that there is some mind-independent object which both senses perceive yet is independent of any particular sense. If it could be heard without being seen and seen without being heard, then it seems to follow it exists without being seen or heard, i.e. mind-independently.

Arguably however Locke hasn’t proven that there is an external world of physical objects, he has merely given some reasons as to how it makes sense of our sense-data for there to be one. Locke claims the fact that we have no choice over our sense-data perceptions shows they are not a part of our mind. However, this is to assume all parts of our mind are under our control. There might be some reason unknown to us why sense-data originating from our mind isn’t under our control. There might also be some reason why we get the same information from different senses, despite them also potentially originating from our mind.

Nonetheless, indirect realism can still be justified by Locke’s arguments if we use Russell’s notion that it is the best hypothesis. The existence of the external world is the best explanation of lack of choice over perceptions and the coherence of various senses.

The argument from Berkeley that we cannot know the nature of mind-independent objects because mind-dependent objects cannot be like mind-independent objects

Indirect realism relies on the claim that our perceptions are mind-dependent sense data which represents mind-independent objects. Berkeley attacks this claim with the likeness principle, which states that to justifiably say that two things to be alike, they must be comparable. But, ideas (mind-dependent) can only be compared to other ideas. There is no way to compare ideas to mind-independent objects and so resemblance between them cannot be justifiably claimed.

Integration: this issue attacks the claim of indirect realism that the objects of perception represent mind-independent objects.

An indirect realist can respond that Berkeley assumes that representation requires resemblance. Arguably there are other methods of representation. For example, the symbols we use in language are completely arbitrary, meaning they have no resemblance to the objects they refer to. The word ‘chair’ does not resemble a chair but nonetheless can represent it. So, mind-dependent objects can be ‘like’ mind-independent objects if we take ‘like’ to involve representation without resemblance.

However, we could defend Berkeley by taking his argument to not be attacking whether an idea could be like a mind-independent object, but whether we could ever be in a position to know that it does. Berkeley seems to be saying that in order for a person to know that an idea is like a mind-independent object, they would have to compare them, yet that cannot be done since we have no direct perception of mind-independent objects. So, no one can justifiably claim that ideas represent mind-independent objects and therefore indirect realism cannot be justified.

Even if we restrict ‘likeness’ to representation, nonetheless our perceptions might not even represent the mind-independent world. It could be totally unlike our perceptions in any respect.

So, we just cannot know whether our perceptions represent mind-independent objects. Indirect realism leads to this sceptical issue, therefore.

Berkeley’s idealism

Berkeley’s attack on the Primary/secondary quality distinction

Berkeley’s master argument

Idealism and the issue of illusions

Idealism claims we perceive ideas directly as they are because to be is to be perceived. The result seems to be that, for example, when we perceive an object like a stick in water appearing bent that it really is bent. Yet, If we reach into the glass to feel that the stick is straight, while also looking at the stick appearing bent, then we perceive two inconstant properties at the same time. It cannot be the case that the stick is both bent and straight. At most one of those properties can be the reality and the other must therefore be an appearance, i.e., sense data. It follows that there is a distinction between appearance and reality. So, it is not the case that to be is to be perceived and therefore Berkeley’s Idealism is false.

Integration: Idealism fails in its claim that to be is to be perceived, which means it is not the case that the objects of perception are mind-dependent ideas.

Berkeley responds that this is a mistake in the language we use to talk about the situation. When we say ‘the stick is bent’ what Berkeley argues we really mean is that it would look bent under normal conditions, which is clearly false. Berkeley suggests instead saying “the stick looks bent”, which is clearly true. An indirect realist would want to insist that although the stick ‘looks’ bent, it isn’t ‘really’ bent – but that is to presuppose that there is a distinction between appearance and reality, which Berkeley has already denied in his attack on the primary/secondary quality distinction. Illusion is only a problem for a theory if it claims that the stick looks bent but is really straight. For Berkeley, there is no way a thing “really is” aside from how it is perceived. It’s not that he denies that it is “really” straight, it’s that he denies there is any way the stick “really is” aside from how it “looks”; how it is perceived.

Integration: Berkeley denies the inference from the stick looking bent to the claim that the stick really is straight. This is a confusion over what Berkeley meant by ‘to be is to be perceived’. To be bent is merely to look bent, not to possess a quality of bentness.

The argument from illusion against idealism begs the question by assuming that there is a distinction between appearance and reality, i.e., a way the stick really is aside from how it appears. The conclusion that idealism leads to an inconsistency between appearance and reality is based on that assumption, which Berkeley does not have to accept. Indeed, in his master argument and attack on the primary/secondary quality distinction he thinks he has given us reason to disregard that assumption.

Idealism and the issue of hallucinations

A hallucination is the perception of an object which doesn’t exist. The possibility of hallucinations pose a problem for idealism because they are subjectively indistinguishable from veridical perceptions. For Berkeley, a veridical perception is when we perceive an idea that is in the mind of God. Yet, hallucinations according to Berkeley come from our imagination, not from God’s mind. While the imagination normally produces voluntary and relatively dim perceptions which are not vivid, Berkeley argues that at times it can produce involuntary and vivid perceptions.

The problem is, if some perceptions are hallucinations from our imagination and they are subjectively indistinguishable from other perceptions, then we can’t tell the difference between hallucination and reality (reality being an idea in the mind of God).

Integration: Berkeley has an epistemological issue, an issue with scepticism, which is a problem for Berkeley as he claimed that defeating scepticism was a reason to accept his theory over indirect realism.

Berkeley responds that hallucinations lack logical connection to the rest of our experience.

However, this response is unsuccessful because some hallucinations might be logically connected to the rest of our experience however. Someone with a fever might look out a window and hallucinate a person walking down the street. There is nothing illogical about that and so no way to tell.

Idealism and the issue of solipsism

Berkeley’s arguments for Idealism conclude that the the objects of perception are mind dependent ideas. When we perceive a mountain or a tree, they have no mind-independent existence as they are just ideas in my mind. The problem is that it’s difficult to see how this would not apply to other people too. It follows that other people are therefore just ideas in my mind. This is called solipsism, the sceptical view that I can only know that my mind exists.

Integration: this issue does not suggest that Idealism is false. It only shows that Idealism leads to this sceptical issue. It somewhat undermines Berkeley’s claim that his theory is superior to the realist theories because it solves issues of epistemological scepticism.

However, Berkeley thinks that Idealism provides an argument for God’s existence which would show that solipsism is false since God also exists, not just my mind.

In the Dialogues, Berkeley argues that God must exist because our ideas must exist in God when not perceived by us. The complexity and regularity of the ideas we perceive shows that they come from God’s mind.

Idealism faces the issue of explaining the regularity of our perceptions, including their apparent continued existence when unperceived.

If I throw a lit match into an empty room, leave it and come back later, the room will have changed.

According to Berkeley however, ‘to be is to be perceived’. Since the room is unperceived it does not exist, yet Idealism is then left with the problem of explaining how it could have undergone change.

Berkeley solves this problem by claiming that God perceives the room and indeed everything other idea, thereby keeping them in existence regardless of whether any human is observing them.

In the Principles, Berkeley argues that once Idealism is established to be true, an argument for God follows as the required causal explanation of our ideas.

If Idealism is true, our ideas cannot be caused by mind-independent objects. The only other options are that they are caused by other ideas, our own minds or another mind.

Ideas are perceived to be passive, to have no causal power, and since to be is to be perceived, ideas have no causal power.

I can cause some ideas through imagination, but others are involuntary and therefore cannot come from my mind.

So by process of elimination, the third option must be true. The involuntary ideas we experience must come from another mind. Berkeley argues that the immeasurable complexity and regularity of the ideas we experience shows that this other mind must be far greater than our own, i.e., God.

This alone counters Solipsism since if God’s mind exists then my mind is not the only mind. However, Berkeley also argues we at least have some evidence to justify thinking other people have minds too. We can infer that on the basis of our own experience of them.

However, If Berkeley’s attack on the primary/secondary quality distinction and master argument fail to establish idealism, or if some other argument proves idealism false, however, then his inference of God would likewise fail. Berkeley’s defence against solipsism relies on his proof of God, which relies on his arguments for idealism. It’s only if Idealism is true that God’s existence is required to explain the regularity of our perceptions and that therefore my mind is not the only one which exists.

Whether God can be used to play the role that he does in Berkeley’s idealism

In Berkeley’s Idealism, God plays the role of perceiving all ideas and causing our ideas. However, since this involves those ideas being in God’s mind, this leads to an issue.

The idea that God could have the same ideas as us is problematic for the traditional view of God. It would mean that God could experience pain, for example. God cannot suffer. Furthermore, God’s ideas are eternal yet ours are transient. God also has ideas of all possible objects, not just the ones that we experience.

Integration: so, it cannot be the case that our ideas originate from God’s mind. Berkeley is therefore left with the sceptical issues of solipsism and accounting for the origin and regularity of our ideas, including their changing when unperceived.