I think it's true that for existentialist thinkers, appreciation of what we are - free, makers of meaning, 'issues' for ourselves, and so on - is at the same time a recognition of how we should try to live.

I was keen to dispel a familiar misunderstanding: that existentialists somehow relish the alienation of human beings from the world. This may have been Camus's attitude, but it was certainly not that of Heidegger, Sartre and Merleau-Ponty, each of whom tried to show that we can only experience the world in relation to our own projects and purposes. The world is initially one of 'equipment', said Heidegger: it is a world of 'tasks', said Sartre.

In the doctrine of the world and humankind as 'will to power and nothing else', Heidegger identified not an antidote to nihilism, but the completion of it. For what can be more destructive of truth and value than the doctrine that these are simply the impositions on the world of human exercises of power?

The dis-incumbenced stance is the one people should cultivate, we are told, once they recognize that there is no world beyond the human world. They will, indeed must, have their beliefs and values, but they will recognize that these 'lean upon' - and are answerable to - nothing other than human commitments and purposes. The only fidelity, Rorty remarked, can be to our own conventions.

The question of meaning goes all the way down: if human life as a whole is meaningless, so is everything that occurs or belongs within it. Since that's not a thought it is easy to live with, there is good reason to search for life's meaning.

My 'heroes' are those - like Chuang Tzu and Heidegger - who recognize that the world of experience is a human world, but recognize too that there is a 'way' or a 'source' to which our lives are answerable.

I'm very sceptical about the prospects for 'big' environmental causes - 'saving the planet', halving the world's population, ending the exploitation of animals, and so on - but a person can ask him- or herself how he or she personally may exercise compassion or humility towards animals, vegetal life and so on.