A couple of thoughts arising from it.
First, as with the painting, I'm seeing the poem on a scale with a novel. What I mean by that is that in some sense there is a whole novel-worth's of information in it. The whole poem can be represented by around 20,000 bits*, but what does that say about the information content of the poem? Surely the poem represents weeks, months, years of work by Yeats. I don't know how long he took to write it, but that is anyway only the tip of the iceberg. In some sense it contains input from all his experience and learning up to the date of composition. And all that input is matched by the output for the reader. That's why I needed the explanation, and why it bears reading and re-reading time after time.
* The text of the poem (with title, line spacing and stanza headings (I, II...)) has 4824 characters. Coded with 7-bit ASCII that would be 33,768 bits. As a text file it was 5141 bytes, which is 41,128 bits. Compressing the text file with winzip got it down to 2666 bytes, which is 21,328 bits.
Second, something totally unrelated, but an observation on something Wood says:
The shock of this moment, this breaking of a vast illusion [in shorthand, this illusion is the 'liberal dream'- my words - but you need to read the whole article], is pictured as having violence at its heart, and indeed as possible only through violence. The picture doesn’t make this or any other violence acceptable or welcome, but it does mean that it’s hard to deny or even deplore the new truth, because the truth is always in one respect an improvement on fantasy – in one respect only, I hasten to add, since fantasy is an improvement on truth in every other way. That is what fantasy is for. Still, this respect is important. One can’t build on error, and with truth there is at least a chance. At the same time this new perception so completely wrecks the past that for the moment the wreck is all that can be seen. Violence is the name of this wreck; it is whatever brings to our minds that knowledge which we cannot and will not gain otherwise. It would be desperate and in a horrible way romantic to believe that there is no other way in which we can ever get the knowledge we need, and we should certainly try to do without uncontrollable mysteries if we can. But it is clear that once days are dragon-ridden, however we explain the arrival of the dragon, neither the past nor the future can be the same.The bits I'm focussing on I've put in bold, but I'm quoting the whole paragraph because increasingly my theme is context, and extracting short quotes is the big crime against context.
Anyway, my point is that you have to be so, so, careful when you start talking about 'truth' and 'error'. Even in science I have problems with, say, Newtonian physics being 'wrong' and relativity being 'right', but all the more in human affairs. Writing in T324 about critical reading, a colleague included in a list of things to be aware of "assumptions about the truth". I think that is so important, and is something we have to be alert to all the time. And assumptions are so-often self-fulfilling. It is like one of the standard ideas of child-rearing: if you assume a child is naughty they will be. If you assume a child is responsible they will be (well, sometimes...).