The Missing Shade Of Blue, subtitled A Philosophical Adventure, is an exploration in the form of a novel of the problem posed by the empirical philosopher David Hume.

Despite his premise that knowledge is derived from sensory experience, he conceded that someone who had seen every colour except one particular shade of blue could conjure up a clear image of that shade from the knowledge of all other shades of blue.

This is something Edgar Logan has puzzled over since his Parisian childhood, when his Scots father turned it into a bedtime story. In Edinburgh to translate Hume's essays into French from the original manuscripts, he is the narrator and one of the three characters around whom the novel is woven.

Edgar's friendship with Harry Sanderson, a philosophy teacher who has become deeply disenchanted with his subject and his much younger wife, Carrie, provides a prism through which Edgar comes to view not only their relationship but the nature of love, which he has so far found only in the pages of novels. Constructing a work of fiction on a philosophical question is a risky enterprise. Ensuring the philosophical dimension remains a vehicle for the literary one requires convincing and evolving characters. Erdal succeeds in this despite giving Edgar a naivety that is difficult to reconcile with his 45 years. The backstory of his childhood in a Paris bookshop, full of family sadnesses, however, provides an explanation for his reclusive nature.

The character of Sanderson dominates with a thrawn contrariness instantly recognisable as a besetting characteristic of generations of Scots. He is a complex creation, whose "iron features, cast in a foundry" belie an inner turmoil. A skin problem, which worsens as the book progresses, simultaneously repels us and attracts our sympathy. It provides a memorable vignette when, conscious of how repugnant it has become, he carries out the physical doctoring of his blistered skin in his office instead of at home and is found by Edgar with his trousers rolled up and his feet encased in polythene bags after he has dipped them in olive oil.

As his skin is ravaged by disease, his mental health is also unravelled by jealousy and despair. The reader is drawn into this process through Edgar's horrified observation of it and Sanderson's moments of lucid self-knowledge. In reflecting on his father's life, for example, Sanderson concedes: "Maybe my father was wiser than Socrates. He worked, he went fishing and he tended his garden." Fishing is important. It is in the contrast between Sanderson's crass fulminating against the modern world and his dextrous fly-tying (in which he delights as a privileged link to an ancient art) that we see how his finer qualities have been submerged by disappointment and feelings of failure.

He is linked just as directly to Hume, who suffered a mental breakdown his doctor termed "the disease of the learned". Where Hume found a remedy in a daily walk, Sanderson finds balm in the perfect casting of a fly into a river and Erdel a metaphor for human behaviour and the setting for a pivotal moment of dramatic tension.

A theme running through this book is what it means to be fully human, something that exercised Hume. For Erdal, the human condition is often absurd. With a shrewd sense of pretentiousness she lightens what occasionally threatens to be a dismal exploration of dark emotions with comic incidents.

This is a debut novel for Jennie Erdal but, as she recounted amusingly and to critical acclaim in her fictionalised memoir, Ghosting, she has written a variety of work including two novels credited to the publisher Naim Attallah. In setting her diffident narrator on his philosophical adventure, she has bravely stretched a difficult idea to its limit and proved herself a serious writer.

The Missing Shade Of Blue

Jennie Erdal, Abacus, £12.99