‘Trillions’ doesn’t add up

‘Oh no, darling’ said my husband, stirring from torpor in his armchair, ‘only about seven ounces of you is bacteria – about the same amount as those little bottles of milk we had at school.’ I had been talking about billions, trillions and quadrillions and had suggested that our bodies’ cells were outnumbered ten to one by bacteria. But since 2016, apparently, the reliable estimate is of 30 trillion human cells with 38 trillion bacteria wandering about inside us.

The language of those large numbers remains ambiguous. In 1974 Harold Wilson, the prime minister, refused a request by a Tory MP for ministers to use billion only in its British meaning of ‘one million million’. ‘No,’ Wilson said. ‘The word billion is now used internationally to mean 1,000 million and it would be confusing if British ministers were to use it in any other sense.’ That has stuck. Rachel Reeves’s headroom may remain £9.9 billion, but that will be 9,900 million, not a thousand times more. The current sense, however, removes the logic of the names billion and trillion. In the first edition of John Locke’s Essay Concerning Humane Understanding (1690), a table gives: ‘Sextilions. Quintilions. Quatrilions. Trilions. Bilions’. Never mind the spelling, the million squared was a billion, as indicated by the prefix bi-; the million to the power of three was the trillion, indicated by the prefix tri-, and so on. Today we must ignore the prefixes and remember that the American economy at $29 trillion is only $29,000,000,000,000.