To start with, let us be clear on one thing: William James cannot save your life. His books, his thought, his dicta are capable of enriching and amplifying the workings of your mind and even of your emotions, if you are suitably receptive. It may even be that the example of how he dealt with his own difficulties may shed a light on how you might deal with your own. But don’t count on it and, above all, don’t expect too much.

It is a pity that John Kaag, professor of philosophy at the University of Massachusetts Lowell and a sensible fellow, chose to burden his valuable little handbook with so silly a subtitle. Amid the welter of self-help texts with which the self-obsessed developed world torments itself, someone should bring out a new, updated edition of James Thurber’s humorous compendium of good sense, the splendidly titled Let Your Mind Alone!

The Jameses were an extraordinary family. Henry James Snr inherited from his father one of the great American fortunes, but had no interest in money for its own sake and no talent for holding on to it, spending his millions lavishly, and recklessly, on his family and himself. One result was that his sons William and Henry were left with the problem of how to make a living and yet carry on the easy and cultivated life their upbringing had accustomed them to, something that came to obsess them. Indeed, William has been criticised for treating not only life in the world but also the life of the spirit as if they were commercial enterprises.

Henry James Snr took the family back and forth across the Atlantic practically every other year. William and Henry, and to an extent their two brothers and their sister, Alice, enjoyed an international education that left Henry with much rich material for his fiction and inculcated in William a broad-minded and ever-inquisitive approach to the world and the creatures in it. Given the family’s gilded circumstances, it was inevitable that the members of it should be deeply neurotic to a man – and to a woman. Poor Alice, who had a mind nearly as fine as those of her two famous brothers, led the life of an invalid and died young of cancer, which, when it came, seemed almost as much an escape route as an affliction.

Henry Snr spent his life addressing the great theological questions that plagued him and seemed to find at least some of the answers he sought, chiefly in the dubious doctrines of the theologian and magus Emanuel Swedenborg. He wrote obsessively and at tremendous length – as a youth William drew a witty sketch of his father vigorously beating a dead horse – and frayed his nerves in the process. In midlife he suffered what he termed a ‘vastation’, a total nervous collapse, which terrified him and markedly sharpened his view of the human predicament. ‘The natural inheritance of everyone who is capable of spiritual life’, he wrote, ‘is an unsubdued forest where the wolf howls and the obscene bird of night chatters.’ Even in extremis, the Jameses could write a fine sentence.

William James in turn experienced a vastation of his own. In Varieties of Religious Experience he provides a report by a ‘French correspondent’ – in reality, himself – that describes how on an ordinary evening, at twilight, ‘suddenly there fell upon me without warning, just as if it came out of darkness, a horrible fear of my own existence’. His terror became embodied in the image of an epileptic patient he had seen in an asylum, ‘like a sculptured Egyptian cat or Peruvian mummy, moving nothing but his black eyes … That shape am I.’

Despite all this, or because of it, James was a remarkably bright and affirmative character, not naturally, but as a result of hard work. Robert Silvers, editor of the New York Review of Books, once asked Isaiah Berlin who his ideal dinner guest would be. Without hesitation Berlin exclaimed, ‘William James!’ And indeed James’s brand of philosophy – pragmatism – has features in common with Berlin’s own thinking on liberty and pluralism. James did not invent pragmatism, though Kaag seems to think he did, not giving credit to its two true founders, Chauncey Wright and Charles Sanders Peirce, the latter of whom so disapproved of James’s interpretation of pragmatism that he renamed his own version ‘pragmaticism’.

James came to pragmatism as a means of grappling with the conundrum of determinism, which insists that, as he wrote, ‘the future has no ambiguous possibilities hidden in its womb … Any other future complement than the one fixed from eternity is impossible.’ This amounts, of course, to a denial of free will. James’s very soul rebelled against the notion that we are little more than robots, fixed in a groove that determines our behaviour and actions to the nth degree, and rejected it with typical and endearing insouciance: ‘My first act of free will shall be to believe in free will.’

James was dead set against jargon and kept his language plain – and, where possible, his concepts too. He made much use of the principle of ‘as if’. Even if we have cause to doubt the possibility of this or that desirable state of affairs, we are free to ignore the doubt. As Kaag writes, ‘Acting as if the world is a welcoming and tender place occasionally has the effect of making it more so.’

Another problem James gave much attention and energy to is the one famously posed by Pontius Pilate: what is the truth? The pragmatist’s answer is subtle, and if on the surface it looks troublingly like a version of relativism, it is not, not really. Kaag states James’s ‘pragmatic maxim’ neatly: ‘truth in ideas is their power to work.’ This would hardly do for, say, a logical positivist, but it did for James: ‘We have to live today by the truth we can get today and be ready tomorrow to call it falsehood.’

Despite some instances of superfluous self-revelation – do we really need to hear about Kaag’s failed marriages? – this short book is an excellent introduction to William James and his philosophy. It is timely, too, given the state of the world as it plunges towards hell in a handcart. Help, even if not of the life-saving kind, is available. As John Kaag beautifully has it, ‘Pragmatism is about life and its amelioration. That’s it.’