The Terror is the terrorist attack on the Twin Towers and the Pentagon last year, and Honderich's book is about how we should respond to that event, and what we should think of our politicians' response. 'We', for this purpose, are the relatively well-to-do inhabitants of the richest countries, and that description of us leads directly to Honderich's message. We should treat the terrorist attack as a reminder of our responsibility for the deaths and bad lives of much of the rest of the world, and we should fulfil our obligation to try to save them from bad lives.

Honderich's case for this conclusion is built on a combination of empirical facts and philosophical theory. The facts are those of absolute and relative deprivation – the average life-span of the least well-off, such as those of sub-Saharan Africa, and their being deprived of the goods of physical well-being, freedom and power, respect and self-respect, relationships with others, and cultural satisfactions.

The facts are compelling, and they culminate in the statistic that if by our actions we had, as we certainly could have, lengthened the lives of the worst-off one-tenth of the population of the worst-off African countries by just five years, we would have prevented a loss of living-time of 20 million years. As Honderich says, the figure "is such as to make all deaths by terrorism, considered only in terms of living-time lost, insignificant."

The philosophical theory which accompanies these facts is a moral position which Honderich has defended elsewhere and which he here calls the 'principle of humanity' – that the right thing to do is what will, according to our best rational judgement, save people from bad lives.

This principle is grounded in what Honderich presents as the facts of 'natural morality': the fact that we desire good things for ourselves and those close to us; the fact that we act on reasons and are therefore subject to the requirement of consistency; and the fact that we have some sympathy for those not close to us.

The principle of humanity is, according to Honderich, the most satisfactory working out of the facts of natural morality. Combined with the facts, it establishes our obligation to give priority to the policies of egalitarian redistribution which are needed to save people from bad lives.

Why is this an appropriate response to 'the terror'? Honderich says that because of "our deadly treatment of those outside our circle of comfort, those with the bad lives...we were partly responsible for the 3000 deaths at the Twin Towers and at the Pentagon."

I am not convinced that he shows the link to be a firm one. He acknowledges that the aims of the terrorists were not the humanitarian ones which he advocates, and I think he underplays the role of religious fanaticism in motivating the attack. But I agree with his practical conclusions, as they are a far more appropriate response to the present world situation than the so-called 'war on terrorism' as it is now shaping up.

It may therefore seem like philosophical nit-picking if I criticise some of his arguments for getting to those conclusions. Still, if the conclusions are the right ones, that's all the more reason for wanting the arguments in defence of them to be the right ones, and there are three points which I think are a bit shaky.

First, he counterposes his principle of humanity to what he calls a 'morality of relationship', but he is a bit inconsistent about this: He says that the fact that many people make sacrifices for the sake of longer and better lives for their children and for others close to them is "something to give us some pride in humankind". When we get to the moral theory, however, he says that the idea that we have special obligations to those close to us is "a strain of selfishness". The first intuition seems to me to be the right one.

The principle of humanity is pretty demanding in the amount of altruism it requires of us. It is said to be grounded in the natural fact of sympathy, but to see it as feasible I think we need to recognise also that our capacities for sympathy start from, and grow outward from, our concern for those close to us.

The morality of humanity will do better justice to the facts of natural morality if it is presented as an extension of, rather than an alternative to, the morality of relationships.

Secondly, Honderich's case for our obligations to save people from bad lives rests on a rejection of the distinction between 'acts' and 'omissions'.

We are as responsible for the bad consequences of what we fail to do as we are for the bad consequences of what we do, he says, and thus "it is hard to see that our omissions with respect to the bad lives are less wrong than the related acts." A couple of pages previously, he has acknowledged that the intentions are different. Most of us haven't, as the terrorists have, intentionally destroyed the lives of others.

The fact remains, he says, "that our omissions can be wrong even if we have something less than a full degree of responsibility for them and even if they come from tolerable or better intentions."

Finally there is the question of terrorism. This has got Honderich into some hot water, mainly because of one paragraph in which he says that "the Palestinians have exercised a moral right in their terrorism against the Israelis." I don't want to debate the point, but simply to note that that statement has to be read alongside his broad definition of 'terrorism'.

He sees no mileage in distinguishing between terrorism and other political violence, and he defines it as "violence with a political and social intention, whether or not intended to put people in general in fear." That hardly captures what most people see as horrific about terrorism: that it kills people indiscriminately, regardless of who they are or what they have done, just because they happen to be convenient targets.

The attack on the Twin Towers was wrong, according to Honderich, because there was no reasonable expectation that it would do any good, only a certainty that it would destroy lives. Is that all? Does that mean it would have been right if it had done some good? Surely what was wrong with it must include the fact that it was an indiscriminate massacre, killing the rich and the poor, the privileged and the oppressed, the innocent and the guilty, for no better reason than that they happened to be in the wrong place at the wrong time.

Other parts of this book are simply splendid: the chapter on the limitations of liberal democracy, and the section demolishing the claims of capitalism in a matter of ten pages, devastatingly put paid to any idea that we can justify the war on terrorism as a defence of our superior 'way of life'.

And the whole book is a marvellous example of what good philosophy can do to puncture the complacency of received moral and political ideas.

After the Terror is available from Amazon (UK).