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Dalhousie University
PHIL 4120
Duncan Macintosh

A.J Ayer/J.L Austen Ayer thinks the theory that – the first thing you’re aware of when you open your mind is an object – cannot explain illusions, delusions – is false. When the brain is stimulated a mental image appears in your minds eye. When you open your eyes, the first thing you’re aware of isn’t the object, but the presence of the object in your mind. (Theory of Indirect Perception) Sense data – non-physical object that exists only in the mind of the observer Ayer argues that all we’re aware of is sense data. Sometimes sense data is caused by things it resembles (accurate perceptions) Representational Theory of Perception, Indirect Theory of Perception • If we’re not aware of the world around us, how do we know it exists? Brings back Descartes problems • Problem: Only • How can a non-physical thing make a causal difference to the brain; if it can send a signal to the brain, it wouldn’t be non-physical - law of physics would be violated • Psychology would be impossible – only you would have knowledge of your own mind • Couldn’t be language Naïve Realism (Theory of Direct Perception) – The first thing you see is the object in the real world Theory of Indirect Perception – The first thing you see isn’t in the real world, but a mental image Sense data – image made up by your mind (ex. dreams), can only be seen by you • Ayer believes you don’t see anything directly from the physical world The Argument from Illusion – Ayer wants to prove sense data, not physical objects • Premise 1 – Everyone will agree that sometimes the mind makes up images of things that aren’t there in the material world (ex. cross eyes & hold up finger, see 2 fingers instead of 1, laws of refraction – stick in the water, dreaming, etc.) • Premise 2 – If it did exist, the experience you have is exactly (qualitatively indistinguishable) like the experience you would have if it did exist (you can’t tell the difference between an actual thing and an illusion) • Premise 3 – Whenever two things look exactly the same, they must be the same kind of thing (when the experiences you have when you misinterpret the world and when you correctly perceive the world look the same, they must be the same kind of thing). If A is indistinguishable from B, then A must be the same kind of thing as B. ex. They are both material objects in the world, or they are not. • Premise 4 - IT CAN'T BE THAT IN BOTH ACCURATE AND INACCURATE PERCEPTION, ONE IS AWARE OF MATERIAL THINGS IN THE WORLD, BECAUSE THERE AREN'T ANY SUCH THINGS IN THE WORLD TO BE AWARE OF IN THE CASE IF INACCURRATE PERCPTION-- E.G., THERE IS NO BENT STICK. SO IN BOTH CASES, IT MUST JUST BE A SENSE DATUM OF WHICH WE ARE AWARE. • Conclusion – Whenever you have any experience at all, accurate or inaccurate, whatever you’re experiencing is a non-material sense data (mental images). Argument from Gradual Transition: In good conditions, we can accurately perceive objects in the world, sometimes inaccurate. We can always construct a continuum of gradual transition between accurate and inaccurate (or the other way around: ex. Approaching mountains – they get bigger as you get closer). Where do you draw the line between real and illusion, if each increment looks just like the last? Therefore, it is all sense data. Argument from Subjective Conditions of Perception: • Some people think when you open your eyes, you’re aware of the material world (i.e. size, shape, colour) • If it were true if you were aware of physical world, the only way to change the material world is to change the physical properties of the physical objects • Ayer argues this isn’t true: Always, whenever you use your senses, what determines our experience isn’t facts about t
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