One of the more embarrassing and self-indulgent challenges of our time is how we can relearn to concentrate. The past decade has seen an unparalleled assault on our capacity to fix our minds steadily on anything. To sit still and think, without succumbing to an anxious reach for a machine, has become almost impossible.

The obsession with current events is relentless. We are made to feel that at any point, somewhere in the globe, something may occur to sweep away old certainties, something that, if we failed to learn about it instantaneously, could leave us wholly unable to comprehend ourselves or our fellows.

We are continuously challenged to discover new works of culture – and in the process don't allow any one of them to assume a weight in our minds. We leave an auditorium vowing to reconsider our lives in the light of a film's values. Yet by the following evening our experience is well on the way to dissolution – just like so much of what once impressed us and which we then came to discard: the ruins of Ephesus, the view from Mount Sinai, the feelings after finishing Tolstoy's Death of Ivan Ilyich.

A student following a degree in the humanities can expect to run through a thousand books before graduation day. A wealthy family in England in 1250 might have had three books in its possession: a Bible, a collection of prayers and a life of the saints – this modestly sized library nevertheless costing as much as a cottage. The painstaking craftsmanship behind a pre-Gutenberg Bible was evidence of a society that could not afford to make room for an unlimited range of works but also welcomed restriction as the basis for a proper engagement with a set of ideas.

The need to diet, which we know so well in relation to food, and which runs so contrary to our natural impulse, is something we now have to relearn in relation to knowledge, people and ideas. We require periods of fast in the life of our minds no less than in that of our bodies.

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