What Are Qualia? The Part of Experience That Resists Description

The term names the felt qualities of experience, the redness of red, the particular character of a smell, the specific unpleasantness of a pain. The claim that these pose a problem rests on an apparent gap, since a complete physical account of what happens when a person sees a ripe tomato describes light, receptors, signals and neural activity, and appears to say nothing about why any of that is accompanied by an experience with that particular character, or indeed by any experience at all. Formulating the difficulty precisely is itself contested, and the standard framing distinguishes the easy problems, which concern explaining functions such as discrimination, reporting and control of behaviour, from the hard problem of why performing those functions is accompanied by experience.

Several thought experiments are used to press the point and each is contested:

• •The knowledge argument, imagining a scientist who knows every physical fact about colour vision while confined to a black and white room, and asking whether she learns something new on seeing red
• •The conceivability argument, asking whether a being physically identical to a person but lacking any experience is coherent, and what follows if it is
• •The inverted spectrum, asking whether two people could have systematically swapped colour experiences while behaving identically
• •The explanatory gap, which claims that no physical account entails why experience accompanies the process
• •The question of what it is like to be an animal with senses we lack, which argues that facts about experience are accessible only from a point of view
• •Each argument has a substantial literature of replies, and none is generally regarded as decisive

Positions divide sharply and each pays a price. Physicalists hold that experience is physical and that the apparent gap reflects a limitation in how we conceptualise rather than a genuine metaphysical divide, with some arguing that we possess two different kinds of concept for the same thing and that the gap between them is cognitive rather than real. Eliminativists hold that the notion is confused and that there is nothing of the kind to explain, which most people find incredible and which its defenders argue is exactly what would be expected of a deeply entrenched mistake. Dualists accept the gap and conclude that experience is not physical, which faces the problem of explaining how the two interact. Panpsychists locate experience as a basic feature of matter, which avoids the emergence problem and creates a difficulty about how small experiences combine into large ones.

Empirical work has not settled the question and has genuinely narrowed the space of tenable positions. Studies identifying which neural activity correlates with a reported experience, and which does not, have produced substantial results, including the finding that a great deal of processing proceeds without any accompanying report and that the difference between processed and experienced is associated with particular patterns of widespread activity rather than with activity in any single region. Theories built on that work make testable predictions about when experience occurs, and several are being compared directly in coordinated experiments designed by their own proponents, which is an unusual and promising arrangement. What such work cannot obviously do is explain why the correlated activity is accompanied by experience at all, which is the point defenders of the hard problem press and critics say dissolves once the functions are fully explained.

The dispute has an unusual character that is worth noticing. Both sides generally agree about the physical facts and about the behavioural facts, and disagree about whether anything further requires explanation, which means no experiment obviously settles it, since any experimental result is available to both interpretations. That has led some to conclude the question is not empirical, others to conclude it is confused, and others to hold that it is a real question that our conceptual apparatus is poorly equipped for. Progress has come mainly from sharpening the arguments and from work in neuroscience that constrains the accounts on offer without settling the central question. Whether the difficulty is permanent, temporary or illusory is itself disputed, which is about as unsettled as a philosophical question gets.

The claim is that a complete physical account of seeing red describes light, receptors and neural activity while leaving out why any experience accompanies it. The knowledge argument, conceivability and the inverted spectrum press that, and each has a large literature of replies. Both sides agree about the physical and behavioural facts and disagree about whether anything further needs explaining.