A metaphor is, of course, a form of figurative language in which an unknown, or lesser known, term is expressly compared to a better known term in order that the latter may illuminate the former. In the language put into common usage by the British critic I. A. Richards, the unknown term is designated the "tenor," while the known term is called the "vehicle."1 A true understanding of metaphor--as Barfield insists throughout his writings (for the nature of metaphor is one of his key subjects)--must evoke the entire evolution of consciousness and requires, in particular, a concomitant understanding of the meaning of literal.2

"In order to have a metaphor," Barfield explains in Speaker's Meaning,

you must begin by being aware of at least two meanings--two meanings, or sets of meanings, which however vague and ill defined they may be in themselves, are not vague, but sharply distinguished from one another; first the lexical, or normal, meaning and, secondly, the speaker's meaning which you now intend the word or phrase "figuratively" to bear. In order therefore to perform the deliberate act of making the outer become a 'vehicle" of the inner, you must first have a word with an exclusively outer meaning.

But it would be a mistake to assume, therefore that the same process has always governed the production of metaphor. A philological investigation into human history reveals no metaphorical period in prehistory, no time when metaphoric language was the norm:

nothing is to be got from the study of language which indicates either that such meanings existed in earlier times or that they are found today in primitive speech. All that the study of language does indicate is that they have come about as part of that historical process which I have called contraction; whereas the use of metaphor always operates to expand meaning. (63-64)

"It is the peculiarity of metaphorical language," Barfield observes, "that, at first sight, it does often resemble very closely the language of participation; though upon closer examination its existence is seen to depend precisely on the absence of participation" (SA 121)

In Poetic Diction Barfield quotes Shelley (from the "Defence of Poetry"):

Metaphorical language marks the before unapprehended relations of things and perpetuates their apprehension until words, which represent them, become, through time, signs for portions or classes of thought, instead of pictures of integral thoughts. (67)

The original "metaphors" which shaped language, Barfield contends, were thus quite distinct from the metaphors produced by conscious minds. Once "the principle of living unity" (as he calls it in Poetic Diction, echoing Shelley) produced the metaphors. Now it is the consciousnesses of individual poets which creates them.

At a later stage in the evolution of consciousness, we find [the principle of living unity] operative in individual poets, enabling them . . . to intuit relationships which their fellows have forgotten-relationships which they must now express as metaphor. Reality, once self-evident, and therefore not conceptually experienced, but which can now only be reached by an effort of individual mind--this is what is contained in a true poetic metaphor; and every metaphor is "true" only in so far as it contains such a reality, or hints at it. The world, like Dionysus, is torn to pieces by pure intellect, but the poet is Zeus; he has swallowed the heart of the world; and he can reproduce it in a living body. (87-88)

Always anxious to refute the tenets of his contemporaries the linguistic analysts, Barfield observes in "The Meaning of 'Literal'" that

There is a school of thought which holds that the tenor of a meaningful metaphor could always, if it were thought fit, be expressed literally. The passenger in the vehicle could, if he chose, get out and walk. If it were not so, these thinkers hold, the tenor would not deserve the name of "meaning" at all; it would amount to no more than an emotional overtone. (RM 34)

In fact something quite different is taking place in metaphoric language:

When we use language metaphorically, we bring it about of our own free will that an appearance means something other than itself, and usually, that a manifest "means" an unmanifest. We start with an idol, and we ourselves turn the idol into a representation. We use the phenomenon as a "name" for what is not phenomenal. And this . . . is just what is characteristic of participation. (SA xxx)

Because "metaphor involves a tension between two ostensibly incompatible meanings," it involves as well "a tension between that part of ourselves which experiences the incompatibles as a mysterious unity and that part which remains well able to appreciate their duality and their incompatibility." "Without the former," we would do well to recall, "metaphor is nonsense language, but without the latter it is not even language" (RM 30).

"A good, a wise, a true metaphor," Barfield insists in "Dream, Myth and Philosophical Double Vision," "is not just a device for lobbing us abruptly out of ordinary into a-consciousness, out of time into eternity, out of the communicable into the ineffable." Rather, the true metaphor

afford[s] us a vision of some particular intermediate stage between the two extremes of the continuum. It trains us in the tensive and laborious problem of adding extraordinary consciousness to ordinary consciousness. It is likely, then, to become more rather than less unpopular with those who are primarily interested in short cuts to bliss. Intermediate stages are not their portion. (RM 30)

See in particular "Language and Discovery" (PD 143-54), "Language and Poetry" (PD 93-101), "Metaphor" (PD 60-76).
1We would do well to remember, Barfield reminds, that "Any specifically new use of a word or phrase is really a metaphor" (PD 112).
2History in English Words provides a plethora of examples of the metaphoric development of our understanding. Here is one:
    The phrase 'high tension,' used of the relation between human beings, is a metaphor taken from the condition of the space between two electrically charged bodies. At present many people who use such a phrase are still half-aware of its full meaning, but many years hence everybody may be using it to describe their quarrels and their nerves without dreaming that it conceals an electrical metaphor-just as we ourselves speak of a man's 'disposition' without at all knowing that the reference is to astrology. . . .

    The scientists who discovered the forces of electricity actually made it possible for the human beings who came after them to have a slightly different idea, a slightly fuller consciousness of their relationship with one another. They made it possible for them to speak of the 'high tension' between them. So that the discovery of electricity, besides introducing several new words (e.g. electricity itself) into our everyday vocabulary, has altered or added to the meaning of many older words, such as battery, broadcast, button, conductor, current, force, magnet, potential, tension, terminal, wire, and many others. (12-13)