Perhaps Basho realized that his art had not yet drunk deeply enough at the well of Zen, for a few years after this poem was written he became a serious Zen student and began to travel around Japan soaking up images. His travel diaries of the last years are a kind of Haiku "poetics," in which he extends the idea of sabi to include the aura of loneliness that can surround common objects. Zen detachment entered his verses; all personal emotion was drained away, leaving images objective and devoid of any commentary, even implied.
More important, the Zen idea of transience appeared. Not the transience of falling cherry blossoms but the fleeting instant of Zen enlightenment. Whereas the antilogic koan anecdotes were intended to lead up to this moment, Basho's Haiku were the moment of enlightenment itself, as in his best-known poem:
Furu-ike ya
An ancient pond
kawazu tobi-komu
A frog jumps in
mizu-no-oto
The sound of water.
These deceptively simple lines capture an intersection of the timeless and the ephemeral. The poem is said to have described an actual occurrence, an evening broken by a splash. The poet immediately spoke the last two lines of the poem, the ephemeral portion, and much time was then devoted to creating the remaining static and timeless part. This was as it should be, for the inspiration of a Haiku must be genuine and suggest its own lines at the moment it occurs. Zen eschews deliberation and rational analysis; nothing must come between object and perception at the critical moment.
With this poem Basho invented a new form of Zen literary art, and Haiku was never the same afterward. To write this kind of poem, the artist must completely disengage—if only for an instant—all his interpretive faculties. His mind becomes one with the world around him, allowing his craft to operate instinctively in recording the image he perceives. For a moment he is privy to the inexpressible truth of Zen—that the transient is merely part of the eternal—and this instantaneous perception moves directly from his senses to his innermost understanding, without having to travel through his interpretive faculties. Earlier Zen writings in both Japan and China had described this process, but none had captured the phenomenon itself. By catching the momentary at the very instant of its collision with the eternal, Basho could produce a high-speed snapshot of the trigger mechanism of Zen enlightenment. In a modern metaphor, the Haiku became a Zen hologram, in which all the information necessary to re-create a large three-dimensional phenomenon was coded into a minuscule key. Any interpretation of the phenomenon would be redundant to a Zen adept, since the philosophical significance would re-create itself spontaneously from the critical images recorded in the poem. Thus a perfect Haiku is not about the moment of Zen enlightenment; it is that moment frozen in time and ready to be released in the listener's mind.