Sir - I wonder where Michael Tyce found the definition of "likely" as the scientific equivalent of "don't know" (Letters, November 30).

The source of this definition was not a qualified scientist, that's for sure. Many of them (qualified scientists, that is) have read Hume and Popper on the nature of knowledge, and even those who haven't do not pretend to be omniscient. They are aware that even a great deal of experimental evidence can never amount to absolute logical certainty. So what they mean when they say "(very) likely" is the cautious but empirically underpinned statement "There is a (very) large and strong body of evidence that supports this hypothesis, much more so than the evidence for the opposite hypothesis". If there is a strong consensus among the highly competitive scientific community that something is very likely, you can rely on it not being a case of "we simply do not know either way". Tyce pooh-poohs the evidence for climate change, claiming that it is nothing more than the desire of the hair-shirt brigade to hamstring 'the economy'. Perhaps another book he should read is one on risk management. Ignoring clear warning signs is not a mark of rational thinking. Or in layman's terms: A stitch in time saves nine.

John Kinory, Steeple Aston