At university, I read Russian and moral philosophy - an ideal combination, or so I imagined for a time. It was clear that Russian literature teemed with moral disorder and existential problems: ungovernable passions, the possibility of redemption, the puzzle of history, the dark shamefulness of the Russian soul (whatever was meant by "soul") and the sheer wretchedness of ordinary people. Philosophy, with its systematic approach to right and wrong, would surely offer a disciplined moral analysis.
It was a naive hope. Moral philosophy was good at asking questions but it soon became clear that far from helping with humanity's suffering, philosophy often appeared to be pitifully disconnected from it. Ditto philosophers. In The Republic, his blueprint for a just and decent society, Plato banned the poets, arguing that only philosophers were fit to govern, since they alone were wholly rational beings, capable of living the good life. Yet a passing acquaintance with the lives of many great philosophers was enough to show that pursuit of reason and virtue did not necessarily lead to a reasonable or virtuous life.
The exception for me was David Hume - a beacon of light and good sense - whose benign spirit, decades later, would hover over my novel The Missing Shade of Blue.
Truth for Hume is not some unworldly abstraction but something to be found in empirical observation. His concern, like that of the novelist, is always with what it is to be human, what it is like to be a particular sort of person. Compassion, faith in human beings, love of the world and freedom from fear- these are all “excellences". He tried all his life to connect with the common man, to make his philosophy more accessible, and to this end even his most difficult abstract ideas are made lucid by ordinary everyday examples, simply put and delivered at a manageable pace, in the tone of intelligent conversation.
According to Hume, all true knowledge derives from sensory experience, which is ultimately all that human beings have access to. The human mind is made up of impressions, deriving from the senses, and ideas, which are "copied" from these impressions. As a striking counter-example to his theory, he introduced the case of "the missing shade of blue" - a way of showing that it is possible, exceptionally, for the mind to generate an idea without first having recourse to the relevant sensory experience. Hume asks us to consider "a person to have enjoyed his sight for 30 years, and to have become perfectly well acquainted with colours of all kinds, except one particular shade of blue". From the contiguous shades, however, Hume concludes that such a person could "supply this deficiency, and raise up to himself the idea of that particular shade". This "missing shade" made a lasting impression on my young student mind and now it is a thread running loosely through my novel.
Other underlying themes - the illusory nature of happiness, the danger of too much thinking, the absence of faith - also owe much to Hume, who saw that the world was painfully disturbed by what he called superstition and enthusiasms. Though later designated the "great infidel", he did not set out with the intention of being an unbeliever. He simply followed the arguments for religion and found them wanting. He was a man primarily interested in explaining our place in the world so that we might live better lives; and the art of living well does not sit happily with clinging to illusions. "Did you ever hear of such madness and folly," he wrote to Adam Smith, "as our clergy have lately fallen into?" That was in 1757 and little has changed.
Another problem Hume encountered early on was how to practise philosophy and still stay sane. As a young man, he had discovered that too much thinking could seriously damage your health. He suffered a breakdown - his physician called it the "disease of the learned" – and it very nearly robbed him of his reason, turning him into "a strange monster", cut off from normal human interaction.
The cure was to be a philosopher but to “be still a man". Which, in practice, meant doing everything more moderately, walking every day, playing backgammon and not thinking too much. He came to understand that a happy life was made up of quite ordinary moments, in the company of friends, eating and drinking together.
During my student years, I used to reflect on this in relation to my own teachers. I had expected academic philosophers to live noble lives, shaped by a disinterested pursuit of virtue and truth. It was before the days when students could be chummy with tutors, so one could only wonder about the life being lived behind the weighty sentences, punctuated by coughs and tics and affectations. Somehow one knew that they had the same fault lines as the rest of us. Reason, as Hume observed, is always the slave of the passions. This is another theme of my novel: that the philosopher - etymologically a lover of wisdom - can also lead a ridiculous life.
By contrast with the philosophers, my father left school at 14 and worked with his hands all his life, building drystane dykes and clearing blocked drains. For him the examined life held no interest or appeal. At my graduation, he took me aside to ask for the first time what I had been doing the past four years. When I told him, he shook his head. "What a waste of time," he said, in his broad Scots tongue. He meant no harm. And next to my tutors, he looked the model of contentment.
Jennie Erdal's "The Missing Shade of Blue" will be published by Abacus (£12.99) on 29 March