Peter Mark Roget, the future Linnaus of the English word, began compiling word-lists at the age of eight. Why was he not playing with other children, honing his social skills? The problem was his mother, a widow at 28, who drained her son of sympathy. Catherine Romilly gave birth to a wonderful, handsome, talented boy , but couldn’t let him be himself. Independence, he would write in his Thesaurus under list 744, equals freedom of action, unilaterality; freedom of choice, initiative. But for freedom see also non-liability, disobedience, seclusion and liberation: the way one insists on freedom in the face of opposition.

Catherine Roget née Romilly came from a well-regarded and successful London Huguenot family blighted by mental illness. After the early death of her Swiss-born husband, Catherine never recovered her capacity for normal life. Her own mother had been mentally incapable and Catherine slipped inexorably into a lesser version of her mother’s state. Shlepping with his sister backwards and forwards between London and the country on the wheels of maternal restlessness, Peter never felt he had a home, except in his wordlists. He worked on them in solitude, while qualifying as a doctor.

Fully fledged at 20, five years too young to practise, he was exceptionally able and also peculiar and solitary. He hated disorder and dirt. When he took a job accompanying two rich teenagers on their European Grand Tour, their notebooks revealed his crabbed and pernickety mind. He taught them to count the windows in cathedrals, and visitor numbers, and tally how many paintings were in a collection. He taught them to structure the world prosaically and reliably; at all costs to avoid emotional surrender. His response to both human and natural life was to classify it, the foundation of his great work to come.

Roget’s next job in London was a desperate couple of months living with Jeremy Bentham, working, in the pre-Bird’s Eye 1820s, on an unlikely project involving frozen food. The cat-loving philosopher was abysmally untidy and there were no locks on the bedroom doors. Addicted to privacy, Roget couldn’t retreat to his own room and his lists without encountering Bentham’s brother and his wife and a lot of cat hair. The born classifier couldn’t get out fast enough.

Then he was a volunteer testing nitrous oxide—laughing gas—as a possible cure for consumption. This was a high-class operation: the other guinea-pigs included Wordsworth…

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