The Chinese Idiom 镜花水月 (the flower in the mirror and the moon in the water) refers to the idea of an epheremal beauty beyond grasp. This idiom was picked up by Izumi Kyoka as the basis for his pseudonym (泉 鏡花).
Zen master Dogen uses the image of the moon in the water twice in his lecture – Genjou Koan.
(For the mind and body have left us with colors that we clutch with our eyes, and the mind and body has left us with voices that we clutch with your ears, and though we are intimate with this entire grasping, it is neither like a mirror catching a shadow, nor like the water and the moon. When a side is revealed, a side is darkened.)
The notes in the English Translation interprets as such:
“Here, Dogen uses the image of ‘the moon in the water’ to refer to something that is only a reflection of the actual object; the phrase is not used in the sense of the common Buddhist metaphor for the Buddha Nature reflected in all things”
“When we are still clinging to things, we do not see the duality inherent within our own thinking and thus we perceive only one side of the duality”.
This paragraph is (to me) talking about how our senses are not as clearcut as a reflection capturing an image. We only grasp a side, while another is always kept in shadow.
Yet, Dogen shifts the image around when he explains his conception of the enligtened man:
人のさとりをうる、水に月のやどるがごとし。月ぬれず、水やぶれず。ひろくおほき(おほき＝大きい Ooki) なるひかりにてあれど、尺寸の水にやどり、全月も彌天も、くさの露にもやどり、一滴の水にもやどる。さとりの人をやぶらざる事、月の水をうがたざるがごとし。人のさとりを罣礙 (Impediment, Hindrance)せざること、滴露の天月を罣礙せざるがごとし。ふかきことはたかき分量なるべし。時節の長短は、大水小水を撿点し、天月の広狭を辦取すべし。
(When a man is enlightened, he is like the moon in the water. The moon isn’t wet, and the water is untouched. Although formed as a massive bulb of light, it rests in a small waterdrop, and even the entire moon and sky are caught in the grass’s dew through the reflection of a single drop. Just as the light of enlightenment breaks not the man, neither too does the moon split the water. A person’s enlightenment does not impede, as a dewdrop’s moon does not impede. The depth will hew to the heights, as to the depth of droplets and the height of moons. And as for how many seasons and times shall pass in the reflection, we look to how far hands can reach into the sizes of the waters, and how much handle can be had upon the longitude of moons.)
In each of these circumstances, how is the moon to be taken?
In the first, for its sad beauty and epheremal inconstancy in the lake.
In the second, it’s referring to the clarity of the representation within the reflected surface and how this is a false view of things.
In the third, it becomes a vision of oneness with nature, where enlightenment sits man to become as much of what he is as possible, rather than disturbing his internal state.
So should we be sad at the image of the moon in the water, or is this, in fact, a sign of a greater and loftier vision of the world? A vision where the image of the moon in a dewdrop contains as much depths as that sphere in the sky, and as much depths in the minds of mens and poets who have used the image for their own purposes.