There is no reason at all to think that creatures with very different purposes and concerns would arrive at the scientific image, and no reason at all to accuse such creatures of getting the world wrong - a point that both Chuang Tzu and Nietzsche make when comparing human and animal perspectives.

What impressed me about Plato and Sartre was their conviction that we should live our lives in the light of big truths about reality and human existence.

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.

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.

Does the unmistakeable intent of Versailles to proclaim dominion over nature destroy its aesthetic appeal, as Schopenhauer thought? Does the greenness of the lawn lose its allure when we learn how much water, sorely needed elsewhere, it uses? And historical shifts in garden taste - from formal, 'French' gardens to 'Capability' Brown's landscapes, for instance, or from the elaborate gardens of imperial Kyoto to Zen 'dry' gardens - register important changes in philosophical or religious attitudes.

Certainly each side - the 'absolutists' and the 'constructivists' or 'humanists', as I've labelled them - accuses the other of hubris, and lays claim to humility. I see hubris on both sides: a pretence that we could ascend to an objective account of the world, on the one hand, and a pretence that we have the resources to live and act without a sense of there being something to which we answerable, on the other. So both sides are 'villains'.

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.