Throughout the history of Rhetoric, metaphor has been treated as a sort of happy extra trick with words, an opportunity to exploit the accidents of their versatility, something in place occasionally but requiring unusual skill and caution. In brief, a grace or ornament or added power of language, not its constitutive form. Sometimes, it is true, a writer will venture on speculations that go deeper ...

[Richards illustrates this with an extended quote from the poet Shelley]

... But that is an exceptional utterance and its implications have not yet been taken account of by rhetoricians. Nor have philosophers, as a body, done much better, though historians of language have long taught that we can find no word or description for any of the intellectual operations which, if its history is known, is not seen to have been taken, by metaphor, from a description of some physical happening.

...

That metaphor is the omnipresent principle of language can be shown by mere observation. We cannot get through three sentences of ordinary fluid discourse without it, as you will be noticing throughout this lecture. Even in the rigid language of the settled sciences we do not eliminate or prevent it without great difficulty. In the semi-technicalised subjects, in aesthetics, politics, sociology, ethics, psychology, theory of language and so on, our constant chief difficulty is to discover how we are using it and how our supposedly fixed words are shifting their senses. In philosophy, above all, we can take no step safely without an unrelaxing awareness of the metaphors we, and our audience, may be employing; and though we may pretend to eschew them, we can attempt to do so only by detecting them. And this is the more true, the more severe and abstract the philosophy is. As it grows more abstract we think increasingly by means of metaphors that we profess not to be relying on. The metaphors we are avoiding steer our thought as much as those we accept. So it must be with any utterance for which it is less easy to know what we are saying than what we are not saying. And in philosophy, of which this is almost a definition, I would hold ... that our pretence to do without metaphor is never more than a bluff waiting to be called. But if that is a truth, it is easier to utter than to accept with its consequences or to remember.