[A very rough and ready introduction of qualia and stuff for the uninitiated].
To our minds, there appears something unique about appearance. There is a ‘what it is like’ component to seeing red, or hearing a sound, or feeling a surface, that seems apart from its physical basis: even if we can explain in complete detail how our sensory apparatus apprehends these stimuli and processes them, the ‘what it is like’, the ‘redness’ is still missing. ‘Redness’ seems a uniquely private sensation, a secondary quality or (in Phil-o-mind speak) a qualia.
Consider the following (fairly famous) thought experiment. Suppose you wake up one morning and find your colour spectrum inverted: when you look at a red object, you see what you’d have called green, the grass looks red, the sea looks orange, and so on. Plausibly, nothing physical need to have happened to your brain – all the neurons could be functioning the same as before. If so, then how are we getting these qualia: how does a felt experience of a colour (or anything else) arise from our neural goings-on?
Indeed, for all we know, you could have an inverted spectrum from me right now: although we both call the same things ‘red’, ‘green’, etc., the qualia you get when you see something we call ‘red’ is the qualia I get when I see something we call ‘green’, and vice versa. (Further, for all anyone knows, everyone might have radically different qualia for everything: although our names might match up to the objects of these qualia, the qualia themselves needn’t match)
Seeing colours differently: Imagine P1 and P2 both seeing an object they both call ‘red’. For all anyone knows, they might have completely different qualia when seeing red. P1s experience of redness might be your experience of greenness, for example. Further, the qualia of one agent might be completely beyond the comprehension of another agent: perhaps you never experience anything like the qualia I experience. Even further, some of us may be philosophically lobotomized: although our brains correctly recognise shapes and make the right motor actions to say the right words, we never actually perceive any qualia at all.
So ‘Redness’ is weird. It is doubly weird because most of us find the following things intuitive: there are only physical objects[ref]Religious beliefs (of whatever stripe) tend to deny this. However, they don’t have a much easier time dealing with the mind. Even if there is non-physical stuff, an account needs to be given for how it interacts with the physical world.[/ref], our minds arise from our physical brains, and the physical universe tootles along by itself according to its own rules, and without intervention or interaction with non-physical forces (philosophospeak: naturalism, physicalism with respect to human beings, and casual closure of the physical). It is hard to find a place for colour in such a world, where to find these experiences in a world of atoms and atom potentials (or, more broadly, where ‘we’ can be found at all – how come there becomes an ‘inside’ or ‘me-ness’ to a particularly sophisticated bunch of neurons?). So long as human organisms shunt out the right behaviour in response to visual stimuli, what need do they have of qualia (or, indeed, consciousness in general?)
This problem is called the ‘hard’ problem of consciousness (in contrast, understanding how the human brain works is considered the ‘soft’ problem: this gives an idea how hard the hard problem is). Qualia like ‘redness’ are possibly the hardest bit of the hard problem (the other contenders are things like intentionality or reference). It is, in Sharon Yang’s professional opinion, a “total mindfuck”.
Here is a very brief survey of the options on the philosophical menu, I’ve neglected to include objections, as many are obvious, and some make the topic (even) harder to understand. This isn’t a perfect characterization, but this exercise is like trying to work out the main contours of a shifting sand dune.[ref]There’s no guarantee I won’t inadvertently mangle the philosophy here, either.[/ref]
Idealism (= it’s all the mind, man):
Given we only ever apprehend the physical world through our mental goings on, one solution is to dump our intuitions about an outside physical world. Instead of a physical world (including brains) in which our minds reside, there is only a mental world, in which all physical objects are illusory. ‘Redness’ is real, and supposed red objects are really to be understood as particular collections of mental states:
Idealism: On idealism, there are no physical objects. The only things that actually exist are mental stuff like qualia or beliefs or whatever. So rather than there being a ‘red box’ out in the world and my mind somehow produces this red qualia from it, now it is rather the complexes of mental stuff that give me the (illusory) impression of my living in a physical world and its objects. Pretty trippy.
Panpsychism (=mind and matter are two sides of the same coin)
If you can’t reconcile things like qualia into the physical world, you can have them run beside it. So although we can see the world in a ‘physics first’ sort of way, with your postbox emitting the right wavelengths of light to hit your retina to go into V1 etc. etc. etc., but also a ‘mental first’ way, with ‘redness’ qualia are beamed into your mind. It is sort of a half way house between idealism (there is only mental stuff, and physical appearances, are, at their core, mental stuff), and physicalism (there is only physical stuff, and mental appearances are, at their core, mental stuff). On this view qualia are out their in the world with their physical counter-parts, and a complete science will, of necessity, include mental properties along side their physical counterparts.
Property dualism (=Mental properties do not depend on our physical brains):
You might like the idea of qualia being a different sort of property to bog standard physical properties, but you might find panpsychism a little bit too hippy in saying qualia are etched into all of reality. So you might want to say that certain arrangements of physical stuff (like brains), are linked up to mental properties (like qualia), but that mental properties do not depend on physical stuff.
An example to make this clearer: consider a tsunami. Most of us would be happy to say a tsunami is nothing but its collection of water molecules (and their velocities etc. etc.) it is no the case there is a special ‘tsunami-substance’ that makes tsunamis – they’re made of water. It also isn’t the case there’s a special ‘tsunami-type’ which obtains in tsunamis. ‘Tsunami’ is nothing but a label we apply to a bunch of water molecules acting in a particular way.
Analogously, a property dualist agrees there is no special ‘mind substance’, but would argue there is a special ‘mind type’, so that our physical understanding is insufficient to understand the goings on in our mind (like redness). We need a new mental science to do that (this view is compared – most often by it’s detractors, to the Vitalism of the 19th Century, that we needed a special ‘life force’ to account for how physical matter could become living things).
Property dualism: Our mental states ‘spring’ from the same (physical stuff), but the properties of our mental lives (like qualia) are not part of physics. The diagram gives one of the popular versions called ‘epiphenomenalism’, which is property dualism with the stipulation that mental properties are casually ineffective. Although our brains might be the substrate for our mental lives, it changes through time by physical laws, and the mental properties ‘dangle down’ from the brain states, but have no role in the brain’s passage through time.
Physicalism (= Mental properties depend on the mind)
The most popular option in philosophy of mind (and perhaps the ‘common sense’ view amongst fairly secular, fairly sciency liberals) is that somehow our mind depends upon our physical brain, and that although qualia like redness appear really weird to a physical point of view, it can none-the-less be reconciled. The very minimal claim a physicalist makes is that mental properties supervene on physical properties. This means that changing the physical state changes the mental state, in the same way changing the pixels illuminated on your computer screen changes the image.
Beyond that, though, all bets are off. Some physicalists say that although mental properties supervene on physical properties, they are not reducible to them: the language that ‘covers’ the physical world cannot ‘cover’ our mental lives, and we need some sort of bridging laws to translate between the two. On these sorts of view, things like redness are emergent properties that occur in certain physical systems. In contrast, reductionism says we can reduce our mental properties into entirely physical language without loss of meaning, and a complete physics will ‘cover’ our mental lives. (At the far extreme, eliminativism says that a complete physics will have no place for things like qualia, and that all talk it and other mental states will go the way of Vital Forces and Aristotelian laws of motion).
Reductionism: In the ‘hierarchy of the sciences’ (which is itself controversial), we think that biology is reducible to chemistry which is reducible to physics: our biology is nothing but the behaviour of its underlying physical constituents and, given enough time, we could translate all biological happenings into physics without losing any explanation. Reductionism (upper) states that our psychological entities (Qualia, beliefs, whatever) are reducible in the same way – we can translate these into a complete biological science, which would in turn be translated into physics, without losing anything from our explanation. Non-reductive physicalism (lower) argues that this is false: there may be bridging laws between our biology and our conscious lives (blue), there is no way we can reduce from the latter to the former. (N.B.) Unlike panpsychists or property dualists, non reductivists think that mental properties are of the same substance and the same type as physical properties – they supervene on physical stuff.
But the mental domain of physical stuff is not explained by a complete physics (in a similar way that the domain of English language might not be explicable in the physics of its letters and sounds), so although mental states don’t need a separate section in the completed book of all substance, nor the completed book of all properties, they do need a new section in the completed book of all science.
One of the other important questions is, if mental properties do depend on physical properties, what is the relationship between them? Is there one-to-one correspondence between a brain state and a state of mind? Or maybe multiple sorts of brain can realize the same mental state, if they share the same functional outcome (you will still ‘see’ red if I replace all your neurons with computationally or representationally equivalent computer chips). Or maybe the translation between brain states and mind states is wholly a priori: once you know all the brain states, and the relevant logical rules, you can know how mental states are ‘hooked up’ to brain states.
Identity (or not): One might think that brain states are identical with mind states (there are other, wierder sorts of identity – one might think there is token identity but not type identity, for example). A popular view is to say instead that mental states are not identical to brain states, but rather identical to some functional state which many brain states could possess (so called ‘multiple realizeability’).
Or something else entirely!
The best introductory book I’ve read is John Heil’s “Philosophy of Mind, A Contempory Introduction”. The routledge “Contemporary Debates in Philosophy of Mind” is a neat mini-review of the state of the field, although much more technical. There are a couple of other ‘introduction of Philosophy of Mind’ like books I have read, but they aren’t as good.
Comprehensible internet resources on Philosophy of Mind are really hard to find (hence why I bothered writing this in the first place). Wikipedia is rubbish, and the Stanford Encylopedia of Philosophy, although clear, is technical. If anyone comes across something fairly accessible, please let me know!