R. H. Blyth, in a very convoluted paragraph tucked away in his little-read volume titled Senryu, gives an ultimately simple definition of the hokku aesthetic that I will put into easily-understandable words:
Hokku is a non-intellectual sensory experience outside the conscious will.
He is talking about what happens when one reads a hokku. We can take, for example, even this late verse by Shiki, who would have called it a haiku, but it is nonetheless just the old hokku:
Seen through the pine boughs —
There is nothing intellectual about it. It is all an experience of the senses, an involuntary sensory experience created in the reader when it is read, a reader who suddenly finds herself or himself looking through green pine boughs at sailing ships passing by on the blue water.
The first line is a basic sensory experience of coolness, felt on the skin. Then comes a visual sensory experience of boughs and ships and water, and the combination of the coolness with the visual sensation makes the whole one simultaneous, non-rational (by which I mean immediate and not thought out) experience.
In the same volume, Blyth also tells us what he means by “Zen” in hokku. I don’t even like to use the term “Zen” today, because it has been so misunderstood, misinterpreted, and sullied by use and over-use. So we can just use the synonym-phrase Blyth gives us:
Simplicity, directness, and non-intellectuality.
If you leave all the other mind baggage aside, and focus just on what is on this page, you will make a great step forward in understanding what hokku is all about.
Shiki also wrote:
With the lamp gone out,
The sound of water.
One does not need to think about it. One just needs to experience it. Moving from “thinking” poetry, which a lot of Western poetry is, to “no-thinking” verse, which is hokku, will give you a completely different way of looking at verse.
Suzushisa ya matsu no hagoshi no hokake bune
Coolness ya pine ‘s needles-seen-through ‘s sailing ship(s)
Suzushisa ya andon kiete mizu no oto
Coolness ya lamp gone-out water ‘s sound