In the preface to vol. 1 of Blyth's Haiku
, "Eastern Culture," he describes two different ways he uses the word "Zen." I think this can be expanded to apply to Buddhism in relation to haiku as well:
"Usually, throughout these volumes, it means that state of mind in which we are not separated from other things, are indeed identical with them, and yet retain our own individuality and personal pecularities. Occasionally ... it [also] means a body of experience and practice ..."
In the history of haiku, there are many haiku which refer to the experiences and practice, as well as the beliefs, of various Buddhist sects. One might say, in that sense, that those are Buddhist haiku.
It is the first meaning that Blyth assigns to his use of the word "Zen" that, in my opinion, creates a problem, and has misled the understanding of the relationship of Zen and haiku in the English-language haiku world.
One doesn't have to be in a Zen state of mind to feel not separated from things, to feel an identification with things outside ourselves. I think poets from pre-literate times to the present have desired to do this and have done it to greater or lesser degrees. I think it is inherent in the very nature of poetry.
The idea of a poet merging with objects outside him/herself became a described state of mind to be consciously pursued during the artistic movement know as Romanticism that emerged in Europe during the late eighteenth and early nineteenth centuries. For instance, the English Romantic poet Samuel Coleridge could write, "...to make the object one with us, we must become one with the object..."
Blyth would likely call this an instance of Zen mind in one who had no overt knowledge of Zen (so far as I know, but then again, Coleridge wrote "Kubla Khan; or, a Vision in a Dream," so who knows?). But that would be misleading in both directions; toward Zen and toward Romanticism. The way Blyth misused the word "Zen" in this sense has led to a significant misunderstanding of the relationship between haiku and Zen in terms of the history and writing of haiku in Japan, for those who have accepted Blyth's position on the subject.
Susumu Takiguchi, for one, thought that Shirane's book, Traces of Dreams
, would become a corrective to this misunderstanding. But the "Zen" of haiku seems to be so embedded in the popular conception of haiku in the English-language haiku world, that I don't think ANY print book can correct the misunderstanding. And now that many people use the internet as their primary source of information, I'm afraid this misunderstanding will persist indefinitely.
P.S. I think that even as Blyth indulged in this misuse of the word "Zen," he was aware of the potential of problems in using the word the way he was. So we have what I consider to be a caveat on Blyth's part, when he writes:
I understand Zen and poetry to be practically synonyms, but as I said before, if there is ever imagined to be any conflict between Zen and the poetry of haiku, the Zen goes overboard; poetry is the ultimate standard.