Lack of clarity and the involuntary misuse of language are the first obvious candidates to account for the pure (or ‘trap–like’) misunderstanding of a set of propositions. It is not necessary to go all the way with more extreme versions of recent linguistic philosophy – ‘I really do think with my pen, because my head often knows nothing about what my hand is writing’ – to see the point of what Bacon had already noticed when he remarked that: ‘Although we think we govern ourwords, and prescribe it well “to speak as the common people do, to think as wise men do”, yet certain it is that words, as a Tartar's bow, do shoot back upon the understanding of the wisest, and mightily entangle and pervert the judgement’.

‘It is impossible to do one thing only’, it is often said. But it is equally impossible to say one thing only. Language speaks – and not always in the exact direction intended by the speaker. The amount of information carried by words and syntax far exceeds what any writer can be aware of. Darwin, for instance, in his already cited reply to Wallace, also acknowledged how he had unwittingly slipped into using the expression ‘natural selection’ in two quite different senses in the text of the Origin – as denoting a process and the outcome of the process – and added: ‘but my blunder has done no harm, for I do not believe that any one, excepting you, has ever observed it’.