The Philosopher's Dog, by Raimond Gaita

Little children are rather casual about ontology. They will pamper a teddy bear while ignoring a human baby, and mourn the loss of a rubber boot more than the death of a pet cat. Junior metaphysicians, it seems, are not impressed by hallowed adult distinctions between animals, vegetables, minerals and people: they see no impermeable barriers between different realms of reality.

When I was very young, for instance, nothing ranked higher in my code of moral precedence than pieces of wood. One day when I was four years old, they tell me, I watched aghast as a helpless old log was hurtled over a flooded weir on the Grand Union Canal. I clenched my fists in agony. "What would you feel like," I demanded through my tears, "if you were a piece of wood?"

Eventually, no doubt, we put such childish things behind us. We learn that inanimate objects can never feel pleasure or pain, let alone embarrassment, gratitude or resentment. Sentimentality and superstition are bred out of us, and when we reach the age of reason we are expected to confine our compassion to the objects that really deserve it – by which we mean, most probably, our fellow human beings, perhaps in proportion to their closeness to us in space and time.

The doctrine that humankind is the only thing that deserves our moral solicitude has a long and imposing pedigree. Religionists of all persuasions agree that we exist as a race apart, and scientific humanists have helped themselves to the same conclusion, though without much of a story to back their dogma up.

In practice, however, very few of us draw the boundary of the moral world as tightly as our theoretical opinions would indicate. There are certain species of non-human animals that it would seem churlish or hard-hearted to leave out: cats and dogs and lambs and ducks can be very persuasive, especially when young, and even slugs and snails have their lugubrious charms. I must admit that my apple tree seems to sigh with pleasure when the pruning saw opens it up to light and fresh air, and surely my flat grumbles its reproaches whenever I neglect it.

So what is the proper scope of moral concern? Who says what kinds of things have a right to rights? Philosophers, who have yet to agree on a definition of human nature, are not about to come up with an answer. And science is not much help either. No amount of genomics will tell us how widely we should spread our affections, and no advances in evolutionary psychology are going to show us how best to express our compassionate instincts.

This kind of intellectual impasse was very familiar to Ludwig Wittgenstein, the austere Austrian genius who, for a period after his death in 1951, was the most revered philosopher in the world. Wittgenstein specialised in giving lucid explanations of how little can be lucidly explained. In the end, he thought, all our attempts at self-justification descend into circularity, and ultimately we have to accept that the norms and assumptions that shape our lives lie far too deep to be touched by mere ratiocination.

The self-denying stoicism of Wittgenstein's philosophy went seriously out of fashion in the Seventies. But a number of devotees have continued to tend the flame – and none more creatively that Raimond Gaita of King's College, London.

His Romulus, my father (1998) was one of the most acute and telling philosophical books of recent years. To all appearances it is a simple filial memoir, evoking the dignity of a handsome Romanian refugee who became a New Australian in 1950, married a dysfunctional wife, and lived a life of poverty, loneliness, betrayal and eventual insanity while looking after various remarkable animals, including the bookish and ruminative son who grew up to write his biography.

But the book is also a work of philosophy, and Gaita's father emerges as a kind of Wittgensteinian paragon, a sage who knew everything worth knowing about honesty, friendship and decency. He was not much of a talker, but his "compassionate fatalism", as Gaita calls it, silently showed others how to live.

In his new book, Gaita elaborates and extends the themes of the earlier one. He describes dozens of animals that have shared his world, and articulates an attitude of grateful respect without ever indulging in sentimental fantasies about the inner mental lives of pets. The Philosopher's Dog is a work of description rather than justification – a literary menagerie arranged to demonstrate the ways in which non-human nature can become part of "the realm of meaning". Take training a dog, for instance: it is not a matter of instilling reliable reflexes, but of creating conditions where friendship and mutual responsibility can grow.

To Gaita, a well-educated dog is not a docile instrument but an active partner, capable of taking initiatives of its own within a "human form of life". A dog is unlikely to entertain grandiose ambitions or suffer the bitter disappointments that give shape to human existences; but its doggy individuality can still warrant our scrupulous respect, not to mention expensive medical attention, a dignified end and, where appropriate, a ceremonious burial.

The real topic of The Philosopher's Dog is not animal existence but human love. Gaita deplores the self-styled animal lovers who project schmaltzy humanoid qualities on to non-human creatures and smother them with indiscriminate affection. Tradition may tell us that love is blind, but if Gaita is right then it is really a source of moral insight: not a subjective feeling, but a form of objective understanding that opens us up to the world.

Forlorn reasoners who equate maturity with heroic independence – with freedom from others, and especially from animals and the rest of nature – are, as he puts it, not "positioned to see things most clearly". Despite a few passages of wistful solemnity, The Philosopher's Dog is an outstanding exercise in seeing things clearly.

Jonathan Rée's book 'I Hear a Voice' is published by HarperCollins