For me, the existentialists are important critics of 'absolutist' claims, and Heidegger and Merleau-Ponty are, at least in their later writings, also exponents of a doctrine of mystery: Being or the 'well-spring' of everything is, for Heidegger, ineffable, just as what Merleau-Ponty called 'Flesh' is for him.

While I am happy to make the occasional foray into educational philosophy - writing, for example, of the difficulty in the contemporary context for a teacher to be 'truthful' - it is more the personal conduct of a life than social institutions that I am concerned to examine.

Like Nietzsche, Heidegger also gave up on the prospect that schools and universities would nurture the kind of reflective openness to the way of things that, certainly by the 1940s, he identified with authentic thinking. The authentic person is not the Promethean, iron-willed figure that pops up in Nietzsche, but someone more like the Daoist sages whom Heidegger admired.

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.

There is something myopic and stunted in focussing only on the meaning of words and sentences. And this myopia is especially unfortunate when combined with a rather abstract view of a language as a set of elements and rules for combining these. For the result is to divorce enquiry into meaning from attention to the way words - and gestures, facial expressions, rituals and so on - are embedded in practices, in what Wittgenstein called 'the stream of life'.

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.

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.