Archive for June, 2013

killer robotThere is a gathering campaign against the production and use of ‘killer robots’, weapons endowed with a degree of artificial intelligence and autonomy. The increasing use of drones by the USA in particular has produced a sense that this is no longer science fiction and that the issues need to be addressed before they go by default. The United Nations recently received a report proposing national moratoria, among other steps.

However, I don’t feel I’ve yet come across a really clear and comprehensive statement of why killer robots are a problem; and it’s not at all a simple matter. So I thought I’d try to set out a sketch of a full overview, and that’s what this piece aims to offer. In the process I’ve identified some potential safguarding principles which, depending on your view of various matters, might be helpful or appropriate; these are collected together at the end.

I would be grateful for input on this – what have I missed? What have I got wrong?

In essence I think there are four broad reasons why hypothetically we might think it right to be wary of killer robots: first, because they work well; second because in other ways they don’t work well, third because they open up new scope for crime, and fourth because they might be inherently unethical.

A. Because they work well.

A1. They do bad things. The first reason to dislike killer robots is simply that they are a new and effective kind of weapon. Weapons kill and destroy; killing and destruction is bad. The main counter-argument at an equally simple level is that in the hands of good people they will be used only for good purposes, and in particular to counter and frustrate the wicked use of other weapons. There is room for many views about who the good people may be, ranging from the view that anyone who wants such weapons disqualifies themselves from goodness automatically, to the view that no-one is morally bad and we’re all equally entitled to whatever weapons we want; but we can at any rate pick up our first general principle.

P1. Killer Robots should not be produced or used in a way that allows them to fall into the hands of people who will use them unethically.

A2. They make war worse. Different weapons have affected the character of warfare in different ways. The machine gun, perhaps, transformed the mobile engagements of the nineteenth century into the fixed slaughter of the First World War. The atomic bomb gave us the capacity to destroy entire cities at a time; potentially to kill everyone on Earth, and arguably made total war unthinkable for rational advanced powers. Could it be that killer robots transform war in a way which is bad? There are several possible claims.

A2 (i) They make warfare easier and more acceptable for the belligerent who has them. No soldier on your own side is put at risk when a robot is used, so missions which are unacceptable because of the risk to your own soldier’s lives become viable. In addition robots may be able to reach places or conduct attacks which are beyond the physical capacity of a human soldier, even one with special equipment. Perhaps, too, the failure of a drone does not involve a loss of face and prestige in the same way as the defeat of a human soldier. If we accept the principle that some uses of weapons are good, then for those uses this kind of objection is inverted; the risk elimination and extra capability are simply further benefits for the good user. To restrict the use of killer robots for good purposes on these grounds might then be morally wrong. Even if we think the objection is sound it does not necessarily constitute grounds for giving up killer robots altogether; instead we can merely adopt the following restriction.

P2. Killer Robots should not be used for any mission which you would not be prepared to assign to a human soldier if a human soldier were capable of executing it.

A2 (ii) They tip the balance of advantage in war in favour of established powers and governments. Because advanced robots are technologically sophisticated and expensive, they are most easily or exclusively accessible to existing authorities and large organisations. This may make insurgency and rebellion more difficult, and that may have undemocratic consequences and strengthen the hold of tyrants. Tyrants normally have sufficient hardware to defeat rebellions in a direct confrontation anyway – it’s not easy to become a tyrant otherwise. Their more serious problems come from such factors as not being able or willing to kill in the massive numbers required to defeat a large-scale popular rebellion (because that would disrupt society and hence damage their own power), disloyalty among subordinates who have control of the hardware, or inability to deal with both internal and external enemies at the same time. Killer robots make no difference to the first of these factors; they would only affect the second if they made it possible for the tyrant to dispense with human subordinates, controlling the repression-bots direct from a central control panel, or being able to safely let them get on with things at their own discretion – still a very remote contingency; and on the third they make only the same kind of difference as additional conventional arms, providing no particular reason to single out robots for restriction. However, robots might still be useful to a tyrant in less direct ways, notably by carrying out targeted surveillance and by taking out leading rebels individually in a way which could not be accomplished by human agents.

A2 (iii) They tip the balance of advantage in war against established powers and governments Counter to the last point, or for a different set of robots, they may help anti-government forces. In a sense we already have autonomous weapons in the shape of land-mines and IEDs, which wait, detect an enemy (inaccurately) and fire. Hobbyists are already constructing their own drones, and it’s not at all hard to imagine that with some cheap or even recycled hardware it would be possible to make bombs that discriminate a little better; automatic guns that recognise the sound of enemy vehicles or the appearance of enemy soldiers, and aim and fire selectively; and crawling weapons that infiltrate restricted buildings intelligently before exploding. In A2 (ii) we thought about governments that were tyrannical, but clearly as well as justifiable rebels there are insurgents and plain terrorists whose causes and methods are wrong and wicked.

A2 (iv) They bring war further into the civilian sphere As a consequence of some of the presumed properties of robots – their ability to navigate complex journeys unobtrusively and detect specific targets accurately – it may be that they are used in circumstances where any other approach would bring unacceptable risks of civilian casualties. However, they may still cause collateral deaths and injuries and in general diminish the ‘safe’ sphere of civilian life which would in general be regarded as something to be protected, something whose erosion could have far-reaching effects on the morale and cohesion of society. Principle P2 would guard against this problem.

A3 They circumvent ethical restrictions The objection here is not that robots are unethical, which is discussed below under D, but that their lack of ethics makes them more effective because it enables them to do things which couldn’t be done otherwise, extending the scope and consequences of war, war being inherently bad as we remember.

A3 (i) Robots will do unethical things which could not otherwise be done. It doesn’t seem that robots can do anything that wouldn’t otherwise be done for ethical reasons: either they approximate to tools, in which case they are under the control of a human agent who would presumably have done the same things without a robot had they been physically possible; or if the robots are sufficiently advanced to have real moral agency of their own, they correspond to a human agent and, subject to the discussion below, there is no reason to think they would be any better or worse than human beings.

A3 (ii) Using robots gives the belligerent an enabling sense of having ‘clean hands’. Being able to use robots may make it easier for belligerents who are evil but squeamish to separate themselves from their actions. This might be simply because of distance: you don’t have to watch the consequences of a drone attack up close; or it might be because of a genuine sense that the robot bears some of the responsibility. The greater the autonomy of the robot, the greater this latter sense is likely to be. If there are several stages in the process this sense of moral detachment might be increased: suppose we set out overall mission objectives to a strategic management computer, which then selects the resources and instructs the drones on particular tasks, leaving them with options on the final specifics and an ability to abort if required. In such circumstances it might be relatively easy to disregard the blood eventually sprayed across the landscape as a result of our instructions.

A3 (iii) Robots can easily be used for covert missions, freeing the belligerent from the fear of punishment for unethical behaviour. Robots facilitate secrecy both because they may be less detectable to the enemy and because they may require fewer humans to be briefed and aware, humans being naturally more inclined to leak information than a robot, especially a one-use robot.

B Because they don’t work well

B1 They are inherently likely to go wrong. In some obvious ways robots are more reliable than human agents; their capacities can be known much more exactly and they are very predictable. However, it can be claimed that they have weaknesses, and the most important is probably inability to deal with open-ended real-life situations. AI has shown it can do well in restricted domains, but to date it has not performed well where clear parameters cannot be established in advance. This may change, but for the moment while it’s quite conceivable we might send a robot after a man who fitted a certain description, it would not be a good idea to send a robot to take out anyone ‘behaving like an insurgent’. This need not be an insuperable problem because in many cases battlefield situations or the conditions of a particular mission may be predictable enough to render the use of a robot sufficiently safe; the risk may be no greater or perhaps even less, than the risk inevitably involved in using unintelligent weapons. We can guard against this systematically by adopting another principle.

P3. Killer Robots should not be used for any mission in unpredictable circumstances or where the application of background understanding may be required.

B2 The consequences of their going wrong are especially serious. This is the Sorcerer’s Apprentice scenario: a robot is sent out on a limited mission but for some reason does not terminate the job, and continues to threaten and kill victims indefinitely; or it destroys far more than was intended. The answer here seems to be; don’t design a robot with excess killing capacity. And impose suitable limits and safeguards.

P4. Killer Robots should not be equipped with capacities that go beyond the immediate mission; they should be subject to built-in time limits and capable of being shut down remotely.

B3 They tempt belligerents into over-ambitious missions. It seems plausible enough that sometimes the capacities of killer robots might be over-estimated, but that’s a risk that applies to all weapons. I don’t see anything about robots in themselves that makes the error especially seductive.

B4 They lack understanding of human beings. So do bullets, of course; the danger here only arises if we are asking the robot to make very highly sophisticated judgements about human behaviour. Robots can be equipped with game-theoretic rules that allow them to perform well in defined tactical situations; otherwise the risk is covered by principle P3. That, at least applies to current AI. It is conceivable that in future we may develop robots that actually possess ‘theory of mind’ in the sense required to understand human beings.

B5 They lack emotion. Lack of emotion can be a positive feature if the emotions are anger, spite and sadistic excitement. In general a good military agent follows rules and subject to P3, robots can do that very satisfactorily. There remains the possibility that robots will kill when a human soldier would refrain from feelings of empathy and mercy. As a countervailing factor the human soldier need not be doing the best thing, of course, and short-term immediate mercy might in some circumstances lead to more deaths overall. I believe that there are in practice few cases of soldiers failing to carry out a bad mission through feelings of sympathy and mercy, though I have no respectable evidence either way. I mentioned above the possibility that robots may eventually be endowed with theory of mind. Anything we conclude about this must be speculative to some degree, but there is a possibility that the acquisition of theory of mind requires empathy, and if so we could expect that robots capable of understanding human emotion would necessarily share it. It need not be a permanent fact that robots lack emotion. While current AI simulation of emotion is not generally impressive or useful, that may not remain the case

C Because they create new scope for crime

C1 They facilitate ‘rational’ crime. We tend to think first of military considerations, but it is surely the case that killer robots, whether specially designed or re-purposed from military uses could be turned to crime. The scope for use in murder, robbery and extortion is obvious.

C2 They facilitate irrational crime. A particularly unpleasant prospect is the possibility of autonomous weapons being used for irrational crime – mass murder, hate crime and so on. When computer viruses became possible, people created them even though thre was no benefit involved; it cannot be expected that people will refrain from making murder-bots merely because it makes no sense.

D Because they are inherently unethical

D1 They lack ethical restraint. If ethics involves obeying a set of rules, then subject to their being able to understand what is going on, robots should in that limited sense be ethical. If soldiers are required to apply utilitarian ethics, then robots at current levels of sophistication will be capable of applying Benthamite calculus, but have great difficulty identifying the values to be applied. Kantian ethics requires one to have a will and desires of one’s own, so pending the arrival of robots with human-level cognition, they are presumably non-starters at it, as they would presumably be for non-naturalistic or other ethical systems. But we’re not requiring robots to behave well, only to avoid behaving badly – I don’t think anything beyond obedience to a set of rules is generally required because if the rules are drawn conservatively it should be possible to avoid the grey areas.

D2 They disperse or dispel moral responsibility. Under A3(ii) I considered the possibility that using robots might give a belligerent a false sense of moral immunity; but what if robots really do confer moral immunity? Isaac Asimov gives an example of a robot subject to a law that it may not harm human beings, but without a duty to protect them. It could, he suggests, drop a large weight towards a human being: because it knows it has ample time to stop the weight this in itself does not amount to harming the human. But once the weight is on its way, the robot has no duty to rescue the human being and can allow the weight to fall. I think it is a law of ethics that responsibility ends up somewhere except in cases of genuine accident; either with the designer, the programmer, the user, or, if sufficiently sophisticated, the robot itself. Asimov’s robot equivocates; dropping the weight is only not murder in the light of a definite intention to stop the weight, and changing its mind subsequently amounts to murder.

D3 They may become self-interested. The classic science fiction scenario is that robots develop interests of their own and Kill All Humans in order to protect them. This could only be conceivable in the still very remote contingency that robots were endowed with full human-level capacities for volition and responsibility. If that were the case, then robots would arguably have a right to their own interests in just the same way as any other sentient being; there’s no reason to think they would be any more homicidial in pursung them than human being themselves.

D4 They resemble slaves. The other side of the coin then, is that if we had robots with full human mental capacity, they would amount to our slaves, and we know that slavery is wrong. That isn’t necessarily so, we could have killer robots that were citizens in good standing; however all of that is still a very remote prospect. Of more immediate concern is the idea that having mechanical slaves would lead us to treat human beings more like machines. A commander who gets used to treating his drones as expendable might eventually begin to be more careless with human lives. Against his there is a contrary argument that being relieved from the need to accept that war implied death for some on one’s own soldiers would mean it in fact became even more shocking and less acceptable in future.

D5 It is inherently wrong for a human to be killed by a machine. Could it be that there is something inherently undignified or improper about being killed by a mechanical decision, as opposed to a simple explosion? People certainly speak of it’s being repugnant that a machine should have the power of life or death over a person. I fear there’s some equivocation going on here: either the robot is a simple machine, in which case no moral decision is being made and no power of life or death is being exercised; or the robot is a thinking being like us, in which case it seems like mere speciesism to express repugnance we wouldn’t feel for a human being in the same circumstances. I think nevertheless that even if we confine ourselves to non-thinking robots there may perhaps be a residual sense of disgust attached to killing by robot, but it does not seem to have a rational basis, and again the contrary argument can be made; that death by robot is ‘clean’. To be killed by a robot seems in one way to carry some sense of humiliation, but in another sense to be killed by a robot is to be killed by no-one, to suffer a mere accident.

What conclusion can we reach? There are at any rate some safeguards that could be put in place on a precautionary basis. Beyond that I think one’s verdict rests on whether the net benefits, barely touched on here, exceed the net risks; whether the genie is already out of the bottle, and if so whether it is allowable or even a duty to try to ensure that the good people maintain parity of fire-power with the bad.

P1. Killer Robots should not be produced or used in a way that allows them to fall into the hands of people who will use them unethically.

P2. Killer Robots should not be used for any mission which you would not be prepared to assign to a human soldier if a human soldier were capable of executing it.

P3. Killer Robots should not be used for any mission in unpredictable circumstances or where the application of background understanding may be required.

P4. Killer Robots should not be equipped with capacities that go beyond the immediate mission; they should be subject to built-in time limits and capable of being shut down remotely.

uploadMichael Hauskeller has an interesting and very readable paper in the International Journal of Machine Consciousness on uploading – the idea that we could transfer ourselves from this none-too solid flesh into a cyborg body or even just into the cloud as data. There are bits I thought were very convincing and bits I thought were totally wrong, which overall is probably a good sign.

The idea of uploading is fairly familiar by now; indeed, for better or worse it resembles ideas of transmigration, possession, and transformation which have been current in human culture for thousands of years at least. Hauskeller situates it as the logical next step in man’s progressive remodelling of the environment, while also nodding to those who see it as  the next step in the evolution of humankind itself. The idea that we could transfer or copy ourselves into a computer, Hauskeller points out, rests on the idea that if we recreate the right functional relationships, the phenomenological effects of consciousness will follow; that, as Minsky put it, ‘Minds are what Brains do’. This remains for Hauskeller a speculation, an empirical question we are not yet in a position to test, since we have not as yet built a whole brain simulation (not sure how we would test phenomenology even after that, but perhaps only philosophers would be seriously worried about it…). In fact there are some difficulties, since it has been shown that identical syntax does not guarantee identical semantics (So two identical brains could contain identical thoughts but mean different things by them – or something strange like that. While I think the basic point is technically true with reference to derived intentionality, for example in the case of books – the same sentence written by different people can have different meanings – it’s not clear to me that it’s true for brains, the source of original intentionality.).

However, as Hauskeller says, uploading also requires that identity is similarly transferable, that our computer-based copy would be not just a mind, but a particular mind – our own. This is a much more demanding requirement. Hauskeller suggests the analogy of books might be brought forward; the novel Ulysses can be multiply realised in many different media, but remains the same book. Why shouldn’t we be like that? Well, he thinks readers are different. Two people might both be reading Ulysses at the same moment, meaning the contents of their minds were identical; but we wouldn’t say they had become the same person. Conceivably at least, the same mind could be ‘read’ by different selves in the same way a single book can be read by different readers.

Hauskeller’s premise there is questionable – two people reading the same book don’t have identical mental content (a point he has just touched on, oddly enough, since it would follow from the fact that syntax doesn’t guarantee semantics, even if it didn’t follow simply from the complexity of our multi-layered mental lives). I’d say the very idea of identical mental content is hard to imagine, and that by using it in thought-experiments we risk, as Dennett has warned, mistaking our own imaginative difficulties for real-world constraints. But Hauskeller’s general point, that identity need not follow from content alone, is surely sound enough.

What about Ray Kurzweil’s argument from gradualism? This points out that we might replace someone with cyborg parts bit by bit. We wouldn’t have any doubt about the continuing identity of someone with a cyborg eye; nor someone with an electronic hippocampus. If each neuron were replaced by a functional equivalent one by one, we’d be forced to accept either that the final robot, with no biological parts at all, was indeed the same continuing person, or, that at some stage a single neuron made a stark binary difference between being the same person and not being the same person. If the final machine can be the same person, then uploading by less arduous methods is also surely possible since it’s equivalent to making the final machine by another route?

Hauskeller basically bites Kurzweil’s bullet. Yes, it’s conceivable that at some stage there will come neurons whose replacement quite suddenly switches off the person being operated on. I have a lot of sympathy with the idea that some particular set of neurons might prove crucial to identity, but I don’t think we need to accept the conceivability of sudden change in order to reject Kurzweil’s argument. We can simply suppose that the subject becomes a chimera; a compound of two identically-functioning people. The new person keeps up appearances alright, but the borders of the old personality gradually shrink to destruction, though it may be very unclear when exactly that should be said to have happened.

Suppose (my example) an image of me is gradually overlaid with an image of my identical evil twin Retep, line of pixels by line. No one can even tell the process is happening, yet at some stage it ceases to be a picture of me and becomes one of Retep. The fact that we cannot tell when does not prove that I am identical with Retep, nor that both pictures are of me.

Hauskeller goes on to attack ‘information idealism’. The idea of uploading often rests on the view that in the final analysis we consist of information, but

Having a mind generally means being to some extent aware of the world and oneself, and this awareness is not itself information. Rather, it is a particular way in which information is processed…

Hauskeller, provocatively but perhaps not unjustly, accuses those who espouse information idealism of Cartesian substance dualism; they assume the mind can be separated from the body.

But no, it can’t: in fact Hauskeller goes on to suggest that in fact the whole body is important to our mental life: we are not just our brains. He quotes Alva Noë and goes further, saying:

That we can manipulate the mind by manipulating the brain, and that damages to our brains tend to inhibit the normal functioning of our minds, does not show that the mind is a product of what the brain does.

The brain might instead, he says, be like a window; if the window is obscured, we can’t see beyond it, but that does not mean the window causes what lies beyond it.

Who’s sounding dualist now? I don’t think that works. Suppose I am knocked unconscious by the brute physical intervention of a cosh; if the brain were merely transmitting my mind, my mental processes would continue offstage and then when normal service was resumed I should be aware that thoughts and phenomenology had been proceeding while my mere brain was disabled. But it’s not like that; knocking out the brain stops mental processes in a way that blocking a window does not stop the events taking place outside.

Although I take issue with some of his reasoning, I think Hauskeller’s objections have some force, and the limited conclusion he draws – that the possibility of uploading a mind, let alone an identity, is far from established, is true as far as it goes.

How much do we care about identity as opposed to continuity of consciousness? Suppose we had to chose between on the one hand retaining our bare identity while losing all our characteristics, our memories, our opinions and emotions, our intelligence, abilities and tastes, and getting instead some random stranger’s equivalents; or on the other losing our identity but leaving behind a new person whose behaviour, memories, and patterns of thought were exactly like ours? I suspect some people might choose the latter.

If your appetite for discussion of Hauskeller’s paper is unsatisfied, you might like to check out John Danaher’s two-parter on it.




dennettProfessors are too polite. So Daniel Dennett reckons. When leading philosophers or other academics meet, they feel it would be rude to explain their theories thoroughly to each other, from the basics up. That would look as if you thought your eminent colleague hadn’t grasped some of the elementary points. So instead they leap in and argue on the basis of an assumed shared understanding that isn’t necessarily there. The result is that they talk past each other and spend time on profitless misunderstandings.

Dennett has a cunning trick to sort this out. He invites the professors to explain their ideas to a selected group of favoured undergraduates (‘Ew; he sounds like Horace Slughorn’ said my daughter); talking to undergraduates they are careful to keep it clear and simple and include an exposition of any basic concepts they use. Listening in, the other professors understand what their colleagues really mean, perhaps for the first time, and light dawns at last.

It seems a good trick to me (and for the undergraduates, yes, by ‘good’ I mean both clever and beneficial); in his new book Intuition Pumps and Other Tools for Thinking Dennett seems covertly to be playing another. The book offers itself as a manual or mental tool-kit offering tricks and techniques for thinking about problems, giving examples of how to use them. In the examples, Dennett runs through a wide selection of his own ideas, and the cunning old fox clearly hopes that in buying his tools, the reader will also take up his theories. (Perhaps this accessible popular presentation will even work for some of those recalcitrant profs, with whom Dennett has evidently grown rather tired of arguing…. heh, heh!)

So there’s a hidden agenda, but in addition the ‘intuition pumps’ are not always as advertised. Many of them actually deserve a more flattering description because they address the reason, not the intuition. Dennett is clear enough that some of the techniques he presents are rather more than persuasive rhetoric, but at least one reviewer was confused enough to think that Reduction ad Absurdum was being presented as an intuition pump – which is rather a slight on a rigorous logical argument: a bit like saying Genghis Khan was among the more influential figures in Mongol society.

It seems to me, moreover, that most of the tricks on offer are not really techniques for thinking, but methods of presentation or argumentation. I find it hard to imagine someone trying to solve a problem by diligently devising thought-experiments and working through the permutations; that’s a method you use when you think you know the answer and want to find ways to convince others.

What we get in practice is a pretty comprehensive collection of snippets; a sort of Dennettian Greatest Hits. Some of the big arguments in philosophy of mind are dropped as being too convoluted and fruitless to waste more time on, but we get the memorable bits of many of Dennett’s best thought-experiments and rebuttals.  Not all of these arguments benefit from being taken out of the context of a more systematic case, and here and there – it’s inevitable I suppose – we find the remix or late cover version is less successful than the original. I thought this was especially so in the case of the Giant Robot; to preserve yourself in a future emergency you build a wandering robot to carry you around in suspended animation for a few centuries. The robot needs to survive in an unpredictable world, so you end up having to endow it with all the characteristics of a successful animal; and you are in a sense playing the part of the Selfish Gene. Such a machine would be able to deal with meanings and intentionality just the way you do, wouldn’t it? Well, in this brief version I don’t really see why or, perhaps more important, how.

Dennett does a bit better with arguments against intrinsic intentionality, though I don’t think his arguments succeed in establishing that there is no difference between original and derived intentionality. If Dennett is right, meaning would be built up in our brains through the interaction of gradually more meaningful layers of homunculi; OK (maybe), but that’s still quite different to what happens with derived intentionality, where things get to mean something because of an agreed convention or an existing full-fledged intention.

Dennett, as he acknowledges, is not always good at following the maxims he sets out. An early chapter is given over to the rules set out by Anatol Rapoport, most notably:

You should attempt to re-express your target’s position so clearly, vividly and fairly that your target says, “Thanks, I wish I’d thought of putting it that way.”

As someone on Metafilter said, when Dan Dennett does that for Christianity, I’ll enjoy reading it; but there was one place in the current book where I thought Dennett fell short on understanding the opposition. He suggests that Kasparov’s way of thinking about chess is probably the same as Deep Blue’s in the end. What on earth could provoke one to say that they were obviously different, he protests. Wishful thinking? Fear? Well, no need to suppose so: we know that the hardware (brain versus computer) is completely different and runs a different kind of process; we know the capacities of computer and brain are different and, in spite of an argument from Dennett to the contrary, we know the heuristics are significantly different. We know that decisions in Kasparov’s case involve consciousness, while Deep Blue lacks it entirely. So, maybe the processes are the same in the end, but there are some pretty good prima facie reasons to say they look very different.

One section of the book naturally talks about evolution, and there’s good stuff, but it’s still a twentieth century, Dawkinsian vision Dennett is trading in. Can it be that Dennett of all people is not keeping up with the science? There’s no sign here of the epigenetic revolution; we’re still in a world where it’s all about discrete stretches of DNA. That DNA, moreover, got to be the way it is through random mutation; no news has come in of the great struggle with the viruses which we now know has left its wreckage all across the human genome, and more amazing,  has contributed some vital functional stretches without which we wouldn’t be what we are. It’s a pity because that seems like a story that should appeal to Dennett, with his pandemonic leanings.

Still, there’s a lot to like; I found myself enjoying the book more and more as it went on and the pretence of being a thinking manual dropped away a bit.  Naturally some of Dennett’s old attacks on qualia are here, and for me they still get the feet tapping. I liked Mr Clapgras, either a new argument or more likely one I missed first time round; he suffers a terrible event in which all his emotional and empathic responses to colour are inverted without his actual perception of colour changing at all. Have his qualia been inverted – or are they yet another layer of experience? There’s really no way of telling and for Dennett the question is hardly worth asking. When we got to Dennett’s reasonable defence of compatibilism over free will, I was on my feet and cheering.

I don’t think this book supersedes Consciousness Explained if you want to understand Dennett’s views on consciousness. You may come away from reading it with your thinking powers enhanced, but it will be because your mental muscles have been stretched and used, not really because you’ve got a handy new set of tools. But if you’re a Dennett fan or just like a thoughtful and provoking read, it’s worth a look.