In fact, the book shows that language is in a rough state of...

In fact, the book shows that language is in a rough state of equilibrium: some words disappear and some structures are eroded, but new ones are created at the same time, and these do the job just as well as the old ones, ... It is true, of course, that decay is one prominent force in the course of language evolution. But there are also forces of creation and generation operating at the same time.