W.B.Yeats - The Symbolism of Poetry (an excerpt)

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I was writing once at a very symbolical and abstract poem, when my pen fell on the ground; and as I stooped to pick it up, I remembered some phantastic adventure that yet did not seem phantastic, and then another like adventure, and when I asked myself when these things had happened, I found, that I was remembering my dreams for many nights. I tried to remember what I had done the day before, and then what I had done that morning; but all my waking life had perished from me, and it was only after a struggle that I came to remember it again, and as I did so that more powerful and startling life perished in its turn. Had my pen not fallen on the ground and so made me turn from the images that I was weaving into verse, I would never have known that meditation had become trance, for I would have been like one who does not know that he is passing through a wood because his eyes are on the pathway. So I think that in the making and in the understanding of a work of art, and the more easily if it is full of patterns and symbols and music, we are lured to the threshold of sleep, and it may be far beyond it, without knowing that we have ever set our feet upon the steps of horn or of ivory*.

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*The gates of horn and ivory are a literary image used to distinguish true dreams (corresponding to factual occurrences) from false. The phrase originated in the Greek language, in which the word for "horn" is similar to that for "fulfil" and the word for "ivory" is similar to that for "deceive". On the basis of that play on words, true dreams are spoken of as coming through the gates of horn, false dreams as coming through those of ivory.