It was an idea long consigned to the dustbin of scientific history. ‘Like a virgin consecrated to God,’ Francis Bacon declared nearly 400 years ago, it ‘produces nothing’. It was anti-rational nonsense, the last resort of unfashionable idealists and religious agitators. And then, late last year, one of the world’s most renowned philosophers published a book arguing that we should take it seriously after all. Biologists and philosophers lined up to give the malefactor a kicking. His ideas were ‘outdated’, complained some. Another wrote: ‘I regret the appearance of this book.’ Steven Pinker sneered at ‘the shoddy reasoning of a once-great thinker’. The Guardian called it ‘the most despised science book of 2012’. So what made everyone so angry?

The thinker was Thomas Nagel, the book was Mind and Cosmos, and the idea was teleology. In ancient science (or, as it used to be called, natural philosophy), teleology held that things — in particular, living things — had a natural end, or telos, at which they aimed. The acorn, Aristotle said, sprouted and grew into a seedling because its purpose was to become a mighty oak. Sometimes, teleology seemed to imply an intention to pursue such an end, if not in the organism then in the mind of a creator. It could also be taken to imply an uncomfortable idea of reverse causation, with the telos — or ‘final cause’ — acting backwards in time to affect earlier events. For such reasons, teleology was ceremonially disowned at the birth of modern experimental science.