When Yeats wrote the word subconsciousness he put it within quotes as ‘subconsciousness’ to mark it as questionable. In his book on the sources of poetry Per Amica Silentia Lunae in the section Anima Mundi: II he writes:
If you suspend the critical faculty, I have discovered, either as the result of training, or, if you have the gift, by passing into a slight trance, images pass rapidly before you. If you can suspend also desire, and let them form at their own will, your absorption becomes more complete and they are more clear in colour, more precise in articulation, and you and they begin to move in the midst of what seems a powerful light. But the images pass before you linked by certain associations, and indeed in the first instance you have called them up by their association with traditional forms and sounds. You have discovered how, if you can but suspend will and intellect, to bring up from the ‘subconscious’ anything you already possess a fragment of. Those who follow the old rule keep their bodies still and their minds awake and clear, dreading especially any confusion between the images of the mind and the objects of sense; they seek to become, as it were, polished mirrors.
According to the old rule all consciousness is permeable because of the unity of being and adepts move freely through its domains. Ritual as the enactment of a symbol draws one into their purlieus. W.H. Auden was indulging himself in a little bladder whacking when he wrote:
To get The Last Poems of Yeats
You need not mug up on dates
All a reader requires
Is some knowledge of gyres
And the sort of people he hates
Auden is a sort of a political poet, “all out of shape from toe to top” the unfair judgement of Yeats on him yet the question hangs in the air: can you read Yeats's poetry waiting on understanding, can you abjure the knowledge of gyres knowing that revelation is at hand?
Before the mind’s eye, whether in sleep or waking, came images that one was to discover presently in some book one had never read, and after looking in vain for explanation to the current theory of forgotten personal memory, I came to believe in a great memory passing on from generation to generation. But that was not enough, for these images showed intention and choice. They had a relation to what one knew and yet were an extension of one’s knowledge. If no mind was there, why should I suddenly come upon salt and antimony, upon the liquefaction of the gold, as they were understood by the alchemists, or upon some detail of cabalistic symbolism verified at last by a learned scholar from his never-published manuscripts, and who can have put together so ingeniously, working by some law of association and yet with clear intention and personal application, certain mythological images. They had shown themselves to several minds, a fragment at a time, and had only shown their meaning when the puzzle picture had been put together. The thought was again and again before me that this study had created a contact or mingling with minds who had followed a like study in some other age, and that these minds still saw and thought and chose. Our daily thought was certainly but the line of foam at the shallow edge of a vast luminous sea: Henry More’s Anima Mundi, Wordsworth’s “immortal sea which brought us hither ... and near whose edge the children sport,” and in that sea there were some who swam or sailed, explorers who perhaps knew all its shores.
Per Amica Silentia Lunae available at Gutenberg - amica