If we consider the leading works of English philosophy written in the age of the scientific revolution, we can hardly fail to be struck by the anxiety they frequently register about what John Locke, in his Essay Concerning Human Understanding, calls the ‘doubtfulness and uncertainty’, the ‘great uncertainty and obscurity’ afflicting the application of moral terms. This sense of increasing ambiguity and confusion about the description and appraisal of human actions was, for example, widespread within the early Royal Society. It underlies John Wilkins's plan of 1668 for the construction of what he called a philosophical language, and it surfaces in the History of the society published by Thomas Sprat in the previous year, in which he complains that the use of ambiguous and over-elaborate language has ‘already overwhelm'd most other Arts and Professions’.

A similar disquiet pervades Locke's analysis in Book 3 of the Essay of what he calls ‘the imperfections and abuses’ of words:

As a result of these confusions, Locke goes on, there is ‘scarce any Name, of any very complex Idea, (to say nothing of others,) which, in common Use, has not a great latitude, and which keeping within the bounds of Propriety, may not be made the sign of far different Ideas’.