From time to time, and in various guises, the issue of de-industrialisation is raised. Sometimes the central concern is the dereliction of a once staple industry, sometimes the effect on UK trade, sometimes the decline of the proportion of GNP related to manufacturing, sometimes a discussion of whether industry matters so much when the rapidly developing sector is now services.
These discussions tend not to start at the beginning, which is assumed, naturally, to be largely known. The terms of the discussion, such as output and productivity, are thus used as if their meanings were perfectly clear. They are not, of course, but no purpose would normally be served by continually rehearsing this, as long as the subject is year to year economic development. When the period concerned is decades and centuries, it is necessary to be more explicit.