Prof. John Searle lectures

Please watch the rest of the videos.

Daniel Dennett on Consciousness

Nice video. Do watch it.

Intentionality article

Good article on Intentionality

http://www.nyu.edu/gsas/dept/philo/faculty/block/papers/qualiagregory.pdf

Qualia

Qualia (singular, quale) is a philosophical term referring to the experiential properties of sensation; the "redness" of red, the "warmness" of warmth, the "garlickness" of the taste of garlic, and so on. By definition, it is impossible to know or understand qualia without direct experience of them, and as a result, they are inherently person-specific and uncommunicable. (One cannot be certain whether or not the "redness" that another sees is experientially identical—or even similar—to the "redness" that one sees, even when looking at the same object.)
The term "qualia" originated in philosophy, although it has been picked up by some scientists (and rejected by some philosophers).

Qualia have become a major component in many modern formulations of the philosophy of mind because of their role in illustrating the difference between knowledge-by-description about, such as might be programmed into a computer, and knowledge-by-acquaintance of, which can only be obtained through direct experience. Computers, like p-zombies, are often assumed to lack qualia and therefore be in some way intrinsically different from humans at a fundamental cognitive level. Whether this is a distinction that actually makes a difference is, apparently, another matter.

Controversies about qualia include:

• Whether qualia exist at all.
• Whether "qualia" is a useful concept/word.
• Whether qualia have interesting epistemological properties, such as being irrefutable and/or ineffable.
• Whether qualia can have unaccountable variations and absences.
• Can computers have qualia.
  • If not, how does that affect AI and mind uploading.
• Whether qualia defy physical explanation/description.
  • If so, whether that is best explained by dualism (qualia are not physical), or by mysterianism

(qualia are physical, but for some reason incomprehensible to humans).
The last dispute is particularly significant. Concern about the problem of qualia (and consciousness in general) is about the only motivation for philosophers to reject physicalism or naturalism that is not propelled by mysticism or religious dogma.


Objectivity and Testability

The concept of qualia has been rejected by some philosophers and neuroscientists as not even wrong, or simply untestable and therefore useless. It also has scientific defenders. It is, after all, hard to dispute that one seems to have qualia, subjectively. One's pain hurts, and one's food has a taste, and so on. Neuroscientist V.S. Ramachandran and philosopher William Hirstein have suggested that one person's qualia could rendered accessible to another once we have the ability to "connect" two brains via some sort of cable. Unfortunately, this technology is a long way off.^[1]
 
Daniel Dennett, like many in the cognitive sciences, characterizes qualia as a useless and unfalsifiable concept, saying that it must be possible to know if a change in qualia occurs and that there is a difference in having a qualia as opposed to not having one.^[2] Simply ignoring any ineffable forms of qualia (or alternatively just redefining them as some measurable property a la Ned Block^[3]) is the de facto position in the cognitive sciences as something must have a measurable effect if you want to do an experiment on it, and consequently, not have your research grant tossed in the garbage bin. Once again, this problem could theoretically be solved if we could hook up two brains Ramachandran-style, but that's currently impossible. As a result, certain versions of qualia tend to be seen as fuzzy or speculative at best with harder versions such as the inverted spectrum tend to be written off as philosophical woo.

 Qualia and Computers


There is, even among naturalists, a widespread apprehension than robots, computers and artificial intelligences would lack human-style emotions, and perhaps even sensation.^[10] It is certainly a staple of science fiction, where androids are by default emotionless, unless of course fitted with an emotion chip. Star Trek's Mr Data is also astonished by "real" touch, when a piece of human skin is grafted onto him by the Borg Queen — whatever tactile sensors he has being fitted with lacking that special something.

Perhaps the origin of the idea lies in the fact that there is no obvious way to program in emotional feelings and sensory qualia. Or perhaps it is because computers and robots are perceived as running on "pure logic", which is seen as a separate faculty to emotion and sensation in humans. A counteragument is that humans are made of matter, and robots are made of matter, and no magic pixie dust is responsible for sensation and emotion in humans.

There are some researchers who think they can programme "artificial qualia" into an AI, but they caution that: a"[w]e are not interested in the problem of establishing whether robots can have real phenomenal experiences or not.^[11]

 What qualia are for
V. S. Ramachandran believes that qualia have a purpose: if an entity has a complex mind with a lot of different things going on, and if it has the ability to manipulate concepts, then it is in danger of paying too much attention to the wrong things, of getting lost in its thoughts. It needs some things to stand out, to be more urgent or compelling than others.^[1] Pain is obviously compelling. Colour is like mental highlighter — in fact, synaesthetes can use mental highlighting to perform some tasks more effectively^[12]. On a related theme, Richard L Gregory has hypothesised that present experience is more vivid than recalled experience because we need to pay attention to the present. If we had perfectly vivide recall of past experience, we might get confused and start reacting to it as though it is happening.<sup>[13]


See the whole article here: http://rationalwiki.org/wiki/Qualia</sup>

Intentionality by Prof. Searle

Cont: Functionalism and consciousness

According to functionalism, one might be tempted to say that a conscious system is a computational system that is capable of posessing functional properties. If we consider Bill Gates, aside from his obvious physical properties, the kinds that any physical thing might have (e.g. his weight, height, his particular chemical composition), one can attribute various properties to him: he is Chairman of Microsoft; he is a computer programmer, etc. Each of these properties are functional properties, and by virtue of having them he is conscious.

Of course, going by that definition, a pocket calculator could be said to be conscious. So it seems that to answer the problem of consciousness, functionalism needs more than a theory of functional processes and properties. Intuitively, consciousness seems linked to the ability to posses functional properties that are capable of producing qualitatively different mental phenomena, what some philosophers refer to as qualia.

But it seems entirely possible, and coherent with functionalism, to suggest that two people could experience entirely different qualia with exactly the same equipment, e.g. two people with the same visual "equipment" could see a block of colour; one could see "red", the other "green" (putting linguistic considerations aside). This phenomenon is known as inverted qualia, and poses no problems for functionalism as such. In fact, in Inverted Earth Ned Block pointed out that one could conceivably render someone unconscious, invert their visual equipment and put them into a room that is identical to that of a second person except that all colours are reversed; in this situation, their qualia would be identical, since what it would be like to experience the colours would be identical for both people, despite their hardware and the reality they are seeing being opposite to one another.

However Block also raised several problems with qualia that affect functionalism in particular. The first is to say that if we accept that inverted qualia pose no problems to functionalism as such, then we must also accept the logical possibility that my visual qualia in a given situation might be identical with your auditory qualia in a given situation, since there is no necessary connection between qualia, the person's hardware and the environment that is 'causing' the experiences. This is both perplexing and attractive to those who feel materialism to be too inhuman, since it suggests that my listening to Beethoven's 5th symphony and your reading a novel set in the Napoleonic wars could evoke exactly the same mental phenomena; what is is like for me to listen to the music could be identical to what it is like for you to read the book. Romantic as this seems, it does make explaining functional states and properties extremely difficult, as you can no longer use the hardware nor the environment as a reliable reference point.

There may also be mental states that aren't public, such as unconscious states, and so that functionalists cannot accurately describe nor explain, at least not objectively, since they cannot get any reliable information by interacting with the owner of the states, they can't look at the brain states, and they can't rely on the subject's environment.

One can also posit the existence of zombies, unconscious beings that have the same behaviour and the same brain states as a conscious being, but no qualia. The functionalist ought to be able to distinguish a zombie from a conscious person, but given that all of the public information seems identical to that of a conscious person, how could one ever know? How could we know everyone else isn't a zombie, or that we ourselves aren't zombies? By being so liberal about qualia and their relation to the brain and the subject's environment, functionalism solves a lot of the problems associated with behaviourism and identity theory, but it also opens the door to extreme forms of scepticism, and makes it extremely unlikely that it could deliver any scientific explanations of the functioning of a specific mind-brain.

John Searle: Consciousness and Causality

http://www.youtube.com/watch?feature=endscreen&NR=1&v=yCii726A4Jc

This is a longer video, but worth watching. Enjoy.

Searle and functionalism

Prof. John Searle. Enjoy this short clip.

The Turing test

Lecture 6: Functionalism

Functionalism emerged in the 1960s from cognitive science, and replaced identity theory and central state materialism as the dominant philosophy of mind. It was developed mostly within the materialist tradition, and is therefore generally considered to be anti-dualist, though this is not necessarily a feature of functionalism.

Functionalism first emerged as a criticism of type-type identity theory, claiming that it was wrong to locate mental phenomena in matter because that implies:

1) Mental phenomena can only be had by beings with a central nervous system similar to ours
2) Beings with similar central state nervous systems must have similar mental states

Functionalism developed the idea that mental phenomena can be had by beings with very different physical constitutions (e.g. humans, cats, computers), and that the same mental phenomena can conceivably be had by physically different beings.

Functionalism's central thesis is that mental phenomena depend not upon the matter in which they 'reside' but in their organisation; i.e. mental states are functional states. A functional analysis of mental phenomena would therefore explain the working of the component parts, or functions, of a psychological organism, and their overall organisation. The mind could therefore be explained in terms of (admittedly complex) flow charts. The mind, and mental faculties, are defined in terms of what they do, rather than what they are, just as one would define 'crank shaft' as 'something that opens and closes valves', rather than identifying the definition with a particular physical object.

Functionalism solves one of the most damaging problems of behaviourism, which is that one could have two stimuli cases providing quite different responses, or indeed several cases of the same stimuli-response relationships with different associated mental states. With functionalism, having the same inputs and outputs needn't mean having exactly the same mental phenomena, since the functions that process the inputs and provide the selfsame outputs can differ. This implies quite a startling conclusion: if one could map out the entire functional process of one thought, one could make a computer 'think' in an identical fashion, and so it is quite conceivable that a machine could love a human, and vice versa.

On this theme, functionalism can be summed up as follows: mind is to brain as software is to hardware. Two systems can be computationally equivalent by physically different.

Is functionalism dualist, materialist or idealist?
By defining itself in terms of function rather than in terms of its substantial instantiations, functionalism remains ontologically liberal (identity theory was thought to be 'chauvinistic') and so avoids the problems of what kinds of beings can have mental phenomena, and of dualism.

Functionalism could be considered compatable with a very liberal token-token identity theory, however, as one could claim that each mental state is identical to a particular physical state (e.g. my pain Y, happening right now, is identical to brain state X) but that mental states in general needn't be thought of as identical to physical states in general (e.g. pain Y is always identical to brain state X).

An identity theory this liberal, however, without the additional ideas of functionalism, becomes more or less meaningless as nothing that it can tell us can ever be proven in any sense (in positing an identity one needs to be able to know of each honomonous entity distinctly, and show a pattern of coincidence with reasons why it is more than coincidence; here one can find no pattern).

It is this distinction between functional states and physical states that leaves functionalism open to forms of dualism, in particular property dualism. Mental phenomena can be thought of as functional properties of brains, with sufficient detachment for entirely different functional states to be associated with the same physical state, and vice versa. In fact, it is conceivable that functionalism might fit with idealist theories. There are no contradictions in functionalism in supposing that a conscious being might have a mind but no brain, and so it is logically possible. Materialism cannot therefore be considered a conceptual truth based on functionalism alone.

Lecture 5: Mental states and processes

To distinguish the faculties of our mind from the features of our brain (which allows for dualism but doesn't necessarily imply it), we can divide our mind into categories of states and processes. Some are ambiguous in their nature, and may be either a state or a process.

Conscious experiences - from these we form beliefs about experiences that may become knowledge. The opposite would be representational experiences, e.g. the knee's reflex, whereby its reaction is merely a representation of the input; no conscious process takes place

Beliefs, desires, emotions

Thought - language representing a conscious experience

Action - the manifestation of a conscious experience in the body; as opposed to mere behaviour based upon representational experience

Unconscious experiences
Interpersonal relationships develop around representations of mental states; I am aware of you, and I know about your various mental conditions. I do not know what it is like to have your mental states, hence relationships are purely representational.

Mental states and processes are susceptible to judgement; this implies some responsibility for our mental states, though in the case of many, this is dubious (e.g. unconscious processes, emotions, and especially actions based on them).

The mind-body problem is essentially this: how are mental states and processes linked to bodily states and processes?

Can a state of mind merely be a bodily state? i.e. can meet experience? What does studying a person's brain tell you about their mind, their experiences and emotions?

Can a state of the body merely be a mind state?

lecture 4: Logical behaviourism

Behaviourism closely followed psychology in the early 20th century, and wanted to concern itself only with publicly observable events and processes in the mind. Along with psychological behaviourists, philosophical behaviourists wanted to resolve the metaphysical nature of the mind and show that terms gained from introspection like 'feeling', 'lived experience' and 'will' are either meaningless or can be boiled down to statements about publicly observable, physical events and processes.

They wanted to construct a semantic theory of the mind that would explain the meaning of mental terms, which could only be achieved by being able to verify if a particular term or statement was accurate or false. Since immaterial notions aren't publicly observable and verifiable, behaviourists concluded that psychology and the philosophy of mind should only concern itself with the material... i.e it is a physicalist theory.

Logical behaviourism therefore holds that any mental term can be understood in terms of observable physical processes or events. For example, if I say I have a toothache, a scientist should be able to point to a problem with my gums, the transmission of information regarding this problem through my central nervous system to my mind, and the characteristic changes in the chemical makeup of my brain. Conversely, if those particular physical events and processes were observed, a scientist would be able to say "he has toothache".

In other words, all meaningful psychological statements are translatable into statements which refer only to physical concepts, without any loss of content; all 'conscious experiences' can be reduced to mere behaviour. Psychological concepts, according to Hempel, serve merely to abbreviate "the description of certain modes of physical response characteristic of the bodies of men or animals" (Hempel, 1980, p.19)
Objection: One can feign a mental state (e.g. actors)

But according to Hempel (1980) a full examination of the central nervous system and other physiological conditions will uncover a feign. But then are there not mental terms, all of whose verifiable criteria can be feigned? In this case, Hempel says, the event or process must be genuine, i.e. if Paul shows all the signs of having the flu, then Paul has the flu.

Objection: How can physical tests capture the qualitative nature of an experience, i.e. what is is to be in pain? Surely such experiences are neither behavioural nor dispositional (e.g. being disposed to be angry), and so can have no physical basis? Even if they do have some physical basis, how can we be sure that the mental states exactly correspond with physical states?

This problem is further complicated by the presence of other people. Let's say I experience the sensation of the colour red, and I find that correlates with a brain state X. Another person then says they are also experiencing the sensation of the colour red, and again we find the same correlation in their brain state. One might conclude from this that the two correlations point to an obvious connection. But how can I know that my mental state is the same as that other person's? Our descriptions might coincide whilst our actual mental states are qualitatively very different, suggesting no connection between mental and brain states, or at least no simple correlative connection.
Behaviourists have no satisfactory response to this objection, since they are interpolating the nature of the mental and brain states from the relationship between inputs and outputs, and so can say nothing of the nature of those states themselves if they are qualitatively different but produce the same measurable behaviour. Wittgenstein discussed this problem by way of the 'beetle in the box' analogy:

(paraphrased)Suppose everyone owns a box, and in each box they keep a 'beetle'. Nobody can see inside anyone else's box, nor know anything of its contents, except that its owner says it contains a 'beetle'. How am I to know my 'beetle' is the same as your 'beetle'? If people then used the term 'beetle' in their language, it couldn't refer to any physical object, and so would, gramatically speaking, drop out of consideration. (Wittgenstein)

In other words, not only can we not know anything about these qualitative experiences, they must in fact be considered non-entities, and so any attempt to explain mental states and processes in physical terms merely through demonstrating correlations in input-output scenarios will be completely flawed.
Though logical behaviourism must be wrong about a lot of things, it does correctly identify the non-contingent, conceptual connection between mental and behavioural descriptions. We learn mental concepts in their application to behaviour, and mental phenomena can often be individuated by their behaviour rather than by their subjective internal features. So there does appear to be a strong connection between behaviour and some mental states and processes, but suggesting that behaviour is all that they are seems far fetched.

Indeed, we can know about our own mental states without needing to observer our behaviour, and often without even observing our own mental states; I know I dislike Big Brother without need for any kind of observation. So logical behaviourism is either asymmetrical in terms of how it suggests we understand mental states and processes, or simply unnatural. This criticism was further developed by Malcolm, who pointed out that if one really were a logical behavourist, one would see people's emotions and mental states merely as physical alterations in the three dimensions, and so one wouldn't see someone as being angry, but as having a particular face. This is enough to know that we aren't logical behaviourists.

Finally, one can undermine the behaviourist thesis by arguing from regress. Suppose a logical behaviourist wanted to explain my belief that it is about to rain. Perhaps I bring the clothes in off the washing line, or put on my coat. To explain that behaviour, the logical behaviourist must make further reference to my belief that I will get wet if I don't put my coat on, and my desire not to get wet, and all in terms of behaviour. Clearly to explain the beliefs and desires, the logical behaviourist will have to go in circles, or run out an extremely long string of behavioural explanations without ever leaving mentions of psychological terminology in the final explanation. It would seem that the ambitions of the reductionist, trying to reduce all psychological terminology into verifiable behavioural terms, are simply too ambitious.

References:

C.G.Hempel, 'The Logical Analysis of Psychology' [originally published in 1935], as reprinted in N.J.Block (ed.), Readings in Philosophy of Psychology, Volume I, (London: Methuen, 1980), p.16

Lecture 3: Identity Theory

Identity theory is a kind of materialism developed as a reaction to work in psychology and the physical sciences in the mid 20th century. It essentially boils down to these statements:

1) Minds are identical to brains
2) Mental states are identical to brain states
3) The realm of the mental is a subset of the realm of the physical

Proponents of this theory state that this claim is a contingent fact about the nature of the mind and the brain; it makes no attempt to explain the meaning of mental terms and so isn't a semantic thesis like logical behaviourism (e.g. 'pain' means physiological state X).

One identity theorist, Smart, claimed that it ought to be a strict identity statement. By this he meant that mind and brain refer to exactly the same thing, i.e. if minds are identical to brains, then brains are identical to minds. Strict identity statements are therefore logically symmetrical. An "un-strict" identity statement would be assymmetrical, for example: rain is identical to bad weather, but bad weather could be rain, sleet, snow, etc.

Identity theory is deemed to be contingent because of the history of the theory. Generally, necessary facts are deemed to be a priori, and so discoverable through study of language, e.g. "one plus one equals two", or "a bachelor is an unmarried man". But because identity theory came from scientific discoveries, the thought is that it cannot be necessary. But then if two things are identical, must that fact not be necessary? One cannot say that in conscious beings on earth, their brains are identical to their minds, but that it is possible that that wouldn't be the case, since that contradicts the theory.
One can however point out that the strength of gravity at the earth's surface is a necessary fact, and yet we only discovered that after thousands of years of scientific investigation. Necessary facts needn't be a priori facts accessible through analysis of language.

Mini lecture 2: Epiphenomenalism

Epiphenomenalism is a position in the philosophy of mind according to which mental states or events are caused by physical states or events in the brain but do not themselves cause anything.

It seems as if our mental life affects our body, and, via our body, the physical world surrounding us: it seems that sharp pains make us wince, it seems that fear makes our heart beat faster, it seems that remembering an embarrassing situation makes us blush and it seems that the perception of an old friend makes us smile.

In reality, however, these sequences are the result of causal processes at an underlying physical level: what makes us wince is not the pain, but the neurophysiological process which causes the pain; what makes our heart beat faster is not fear, but the state of our nervous system which causes the fear etc.

According to a famous analogy of Thomas Henry Huxley, the relationship between mind and brain is like the relationship between the steam-whistle which accompanies the work of a locomotive engine and the engine itself: just as the steam-whistle is caused by the engine’s operations but has no causal influence upon it, so too the mental is caused by the workings of neuro-physiological mechanisms but has no causal influence upon their operation.

More...
 
The doctrine that consciousness, or mind, is an added or secondary phenomenon (epiphenomenon); the doctrine that consciousness is the incidental result of the phenomena of neural structure and of neural activity according to the laws of mechanics. 

 According to this view, freedom and responsibility are illusions or a routine, having no more real relation to conduct than has the sound of the bell to its tolling or the whistle of the engine to its movements. 

The aim of science is held to be the objective study of a material universe, into which our minds must not be thrust as part of the problem, which is complete and intelligible only when considered objectively and as separated from our minds by a chasm that is intellectually impassable. 

Sensible knowledge is held to consist of phenomena or appearances which are produced in our minds by a natural world that in itself is, and always must be, utterly unknown and unknowable; and as the human brain is part of the phenomenal world of appearances in our minds, critical epiphenomenalism resolves itself into the assertion that our minds are the by-products of appearances in our minds, produced by we know not what.

Lecture 1: Mind and Body Problems

Mind–body dualism,  in philosophy, any theory that mind and body are distinct kinds of substances or natures. This position implies that mind and body not only differ in meaning but refer to different kinds of entities. Thus, a dualist would oppose any theory that identifies mind with the brain, conceived as a physical mechanism.

The modern problem of the relationship of mind to body stems from the thought of René Descartes, a 17th-century French philosopher and mathematician, who gave dualism its classical formulation. Beginning from his famous Cogito, ergo sum (Latin: “I think, therefore I am”), Descartes developed a theory of mind as an immaterial, nonextended substance that engages in various activities such as rational thought, imagining, feeling, and willing. Matter, or extended substance, conforms to the laws of physics in mechanistic fashion, with the important exception of the human body, which Descartes believed is causally affected by the human mind and which causally produces certain mental events. For example, willing the arm to be raised causes it to be raised, whereas being hit by a hammer on the finger causes the mind to feel pain. This part of Descartes’s dualistic theory, known as interactionism, raises one of the chief problems faced by Descartes: the question how this causal interaction is possible.

This problem gave rise to other varieties of dualism, such as occasionalism and some forms of parallelism that do not require direct causal interaction. Occasionalism maintains that apparent links between mental and physical events are the result of God’s constant causal action.

Parallelism also rejects causal interaction but without constant divine intervention. Gottfried Wilhelm Leibniz, a 17th-century German rationalist and mathematician, saw mind and body as two perfectly correlated series, synchronized like two clocks at their origin by God in a preestablished harmony.

Another dualistic theory is epiphenomenalism, which agrees with other theories in holding that mental events and physical events are different. The epiphenomenalist holds, however, that the only true causes are physical events, with mind as a by-product. Mental events seem causally efficacious because certain mental events occur just before certain physical events and because humans are ignorant of the events in the brain that truly cause them.

Among the difficulties of dualism is the inherent obscurity in conceiving of what sort of thing a mental substance—an immaterial, thinking “stuff”—might be. Such criticisms have led some thinkers to abandon dualism in favour of various monistic theories.

  What are minds, and how are they related to bodies and other physical stuff?

Descartes’ Dualism
    
Descartes contends that a person or human being such as you or me is a two-part composite, of a mind and a body.  (Alternatively speaking, the person is just the mind but has a body.)  And according to him, a mind is an entirely immaterial, nonphysical thing, not even located in physical space.  Yet what unites a mind with a particular body is that it causally interacts with that body, in a distinctively intimate way.
    
His main argument is this:
            1.  I can doubt that my body [or any other physical thing, such as my brain, or anything with any spatial properties] exists.
            2.  I cannot doubt that my mind exists.
        __________________________________________________
         \ 3.  My mind is distinct from my body [and from every other physical thing, such as my brain, or anything with any spatial properties].   [1,2]

Thus, your mind and its states are simply not physical. 

The Interaction problem.  How could a thing so utterly nonphysical as a Cartesian mind directly affect your physical body, or be directly and intimately affected by it? Descartes first appealed to the pineal gland, as the gateway or locus of mind-body interaction.
The pineal gland is just another physical entity; so that appeal is no answer to the question of how a Cartesian mind could interact with anything physical.  Descartes then likened mental causation to the force of gravity; gravity isn’t a physical object like a billiard ball or a fist, yet it causes physical motion.  But gravity is physical in at least the weaker sense that a gravitational field is always the gravitational field of some physical object; also gravity is physical in Descartes’ own favorite sense of being a spatial phenomenon and working according to well known laws of physics.  The trouble with Cartesian minds is that they do not have any spatial properties at all.

Cartesian minds fit ill with our otherwise physical and scientific picture of the world, uncomfortably like ghosts or ectoplasm.  They are not needed for the explanation of any publicly observable fact, for neurophysiology promises to explain the motions of our bodies in particular and to explain them completely.  Ghost-minds are scientific excrescences. Cartesian minds are not scientific posits, hypothesized to explain physical events.  They are known from the inside, and shown to be nonphysical by Descartes’ Doubt argument.  If they’re scientifically ill-behaved, too bad. 

Cartesian Doubt: Cartesian doubt is methodological. Its purpose is to use doubt as a route to certain knowledge by finding those things which could not be doubted. The fallibility of sense data in particular is a subject of Cartesian doubt.
René Descartes, the originator of Cartesian doubt, automatically put all beliefs, ideas, thoughts, and matter in doubt. He showed that his grounds, or reasoning, for any knowledge could just as well be false. Sensory experience, the primary mode of knowledge, is often erroneous and therefore must be doubted. For instance, what one is seeing may very well be a hallucination. There is nothing that proves it cannot be. In short, if there is any way a belief can be disproved, then its grounds are insufficient. From this, Descartes proposed two arguments, the dream and the demon.
Descartes, knowing that the context of our dreams, while possibly unbelievable, is often life-like, hypothesized that humans can only believe that they are awake. There are no sufficient grounds by which to distinguish a dream experience from a waking experience. For instance, Subject A sits at her computer, typing this article. Just as much evidence exists to indicate that her composing this article is reality as there is to demonstrate the opposite. Descartes conceded that we live in a world that can create such ideas as dreams. However, by the end of The Meditations, he concludes that we can distinguish dream from reality at least in retrospect
Descartes reasoned that our very own experience may very well be controlled by an evil demon of sorts. This demon, or genius, is powerful enough to control anybody. He could have created a superficial world that we may think we live in.