If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content
Current time:0:00Total duration:7:22

Epistemology: Paradoxes of Perception #2 (Argument from Hallucination)

Video transcript

hi I'm orgone Fisher read and philosophy at the University of East Anglia in this miniseries we're looking at paradoxes that engender a classical philosophical problem about perception these paradoxes are persuasive arguments delete from uncontroversial assumptions to a disquieting conclusion we typically believe that we can just see the tables chairs and kitchen knives that surround us in our domestic environment but paradox is known as arguments from illusion and from hallucination have us conclude that we're never directly aware of such physical objects that we are cut off from the physical things around us by a veil of subjective images perceptions or sense data in the previous video we had a look at the argument from illusion which considers cases where physical objects appear a different shape size or color than they are as when we view round coin sideways so they look elliptical we now turn to the argument from hallucination this argument considers cases what we find it natural to say that people see or hear things even though nothing of the sort is around to be seen or heard the simple version of the argument starts out from the observation that such cases actually occur for example people with schizophrenia often hear voices when nobody in their vicinity is speaking the words they hear the voices they're here are therefore not those are speakers addressing them in the flesh or think of visual hallucinations like that of Shakespeare's Macbeth who in a fit of madness or intense anxiety seized a dagger before him when no such physical object is actually there to be seen the dagger disease therefore cannot be a physical object when having such hallucinations people must see and hear something else not material objects or people around for everyone to see or hear but immaterial object of awareness of which only the hallucinating subject is aware these non-physical private objects of awareness or called sense data at any rate in cases of hallucination subjects are aware of such sense data of them the physical objects there are also non clinical cases where we find it natural to say that people see things that are not there to be seen these include cases that psychologists technically classify as optical illusions have a look at the famous Hermann grid at the intersections you will see spots each spot disappears the moment you look directly at it and reappears the moment you shift the focus of your gaze these spots have a more fleeting existence than physical objects they are census data like the argument from illusion the argument from hallucination first argues that people are aware of sense data rather than physical objects in particular cases and then generalizes in the second step from these particular cases to all cases of seeing hearing etc surely the argument from hallucination continues to patients with schizophrenia hearing voices feels exactly like hearing people who are actually speaking to them the voices are for instance every bit as loud and distinct as those of people actually talking in the room similarly to macbeth hallucinating the dagger is exactly like actually seeing a physical dagger that's why he reaches for it those afflicted cannot tell any difference between the hallucinatory experiences and ordinary perceptual experiences like hearing others talk or seeing the weapon of choice but simple reasoning suggests that experiences which feel or seem alike should be experiences of the same kind of thing after all the reasoning goes private sense data which nobody else can see or hear are radically different from public physical objects and noises which anyone around can notice and surely being aware of such radically different things cannot feel exactly the same to people therefore if the subject is aware of a private sense datum in the case of hallucination she must be aware of a private sense datum also in cases of ordinary perception feel or see just the same to her the second main step of the argument clearly does not work well for non clinical cases of hallucination like the Hermann grid your experience of seeing gray spots at it's white intersections is certainly not like the experience of seeing gray patches of paint physically applied to those intersections when you focus on them you still see the paint patches but not the gray spots that served as examples of sense data indeed most proponents of the argument just don't know to what extent this is different in clinical cases they don't know whether to a person with schizophrenia hallucinating a dagger really is like actually seeing a dagger this motivates a hedge this hedge and a clarification lead to a less simple version of the argument 20th century analytic philosophers like Freddie aya assume only that it is possible for us to have hallucinatory experiences which are just like the experience we have say when actually seeing a dagger they also clarify that the argument is not using the verb to see and ordinary literal sense to say what we aspire with our eyes in this ordinary sense it implies that there is something there to be seen so of course Macbeth does not see a dagger in this sense since there is no dagger there for him to see the less simple version of the argument therefore explicitly introduces an extended phenomenal sense of the verb in this extended sense the verb is used to describe a person's experience without implying anything about a physical environment so when Shakespeare describes a possible experience which is just like that of seeing a dagger we can legitimately describe that experience by saying that Macbeth saw a dagger but the argument goes in the conspicuous absence of a physical dagger we cannot say that Macbeth sees the physical object the so-called dagger he sees must be a sense datum if the possible experience described by Shakespeare is just like an actual experience of seeing a physical dagger and the two experiences should involve awareness of the same kind of object if Macbeth is aware of a sense datum when hallucinating it he should be aware of a sense Tatum also when seeing a physical dagger to generalize yet further we know that for any experience of seeing or hearing something there is a possible hallucinatory experience which is just like it so if these possible experiences involve awareness only of sense data then we are aware of sense data whenever we see or hear anything physical objects might hide behind their veil but stare at them as intently as we might we can never just see the physical things that presumably surround us you