In Rinzai training the method of koan practice is well-known and highly developed. Most students, if suited to it, will take up this method at some point.
However, many beginners do not realize that what we generally call "koan practice" actually contains several different ways of practicing. We may sometimes differentiate, for example, between practice centered on one of the classic koan cases in their entirety, and practice focusing on a word or phrase - the wato, or "word head" - of a koan. The famous practice centered on the word Mu is in fact a wato taken from the first koan in the Mumonkan. The phrase "Who [or what] am I?" is another common wato - not taken from a koan - which is often assigned.
It is useful to differentiate wato and koan practice in this manner because the way in which one engages in kufu - struggle, or grappling - with different wato and koan must flexibly change. All wato and koan are taken up within the samadhi cultivated in Zen practice, and some will require conceptual engagement and expression. However, the initial koan or wato in particular has the function of leading us to cut off conceptual fixation and recognize the original face of self-awareness, that is, to have the experience called kensho which is the entrance gate to authentic Zen training. It must therefore be taken up completely with the body.
These points may also help us to understand the difference between samadhi before kensho and samadhi
after kensho; that is, between training to remove obstructions to wisdom
and eventually point it out, and the long training after awakening to
clarify, refine and integrate wisdom. Both trainings are undertaken in
samadhi, but only a samadhi manifesting in unity with wisdom is the true
Zen samadhi, able to freely use words and concepts without fixation.
I have used rather technical language here, and beginners don't really need to worry too much about it. But they do need to find out, within their own bodies, how to enter into the samadhi of the initial wato or koan. A student given the wato Mu from that famous first case in the Mumonkan is not to approach it conceptually, trying to understand why Joshu said "No" when asked if dogs have Buddha nature (or why on another occasion he said "Yes," and so on). In other words, the purpose of taking up the wato Mu is not to engage conceptually with Buddha-nature theory and its theorized application to canines! The purpose of this method, rather, is to cause us to enter the gate of Zen awakening for ourselves.
How to do it, then? Students should apply the instructions received from their teachers regarding use of the body and breath to gather the wato together with the energetic currents at the tanden (the navel energy center). These are details which are transmitted through oral instruction. However, regarding the general method and the way in which one should approach it, Mumon - the compiler of the Mumonkan - tells us what to do in his commentary to that first case of Joshu's Mu.
I have been recommending to several students recently that they read and re-read this commentary. Even if they are not working with the Mu wato but something else like "Who am I?", the advice still holds. It is actually very kind advice, to be taken quite literally. It points out in a manner which is easy to understand - though not necessarily easy, in the beginning, to do - how to work with the wato:
In order to master Zen, you must pass the
barrier of the patriarchs. To attain this subtle realization, you must
completely cut off the way of thinking.
If you do not pass the barrier, and do not cut
off the way of thinking, then you will be like a ghost clinging to the bushes
Now, I want to ask you, what is the barrier of
Why, it is this single word "Mu." That
is the front gate to Zen.Therefore it is called the "Mumonkan of
Zen." If you pass through it, you will not only see
Jõshû face to face, but you will also go hand in hand with the
successive patriarchs, entangling your eyebrows with theirs, seeing with the
same eyes, hearing with the same ears. Isn't that a delightful prospect? Wouldn't you like to pass this barrier?
Arouse your entire body with its three hundred
and sixty bones and joints and its eighty-four thousand pores of the skin;
summon up a spirit of great doubt and concentrate on this word "Mu." Carry it continuously day and night. Do not form
a nihilistic conception of vacancy, or a relative conception of "has"
or "has not."* It will be just as if you swallow a red-hot iron
ball, which you cannot spit out even if you try. All the illusory ideas and delusive thoughts
accumulated up to the present will be exterminated, and when the time comes,
internal and external will be spontaneously united. You will know this, but for
yourself only, like a dumb man who has had a dream.
Then all of a sudden an explosive conversion
will occur, and you will astonish the heavens and shake the earth. It will be as if you snatch away the great sword
of the valiant general Kuan and hold it in your hand. When you meet the
Buddha, you kill him; when you meet the patriarchs, you kill them. On the brink
of life and death, you command perfect freedom; among the sixfold worlds and
four modes of existence, you enjoy a merry and playful samadhi.
Now, I want to ask you again, "How will you
carry it out?" Employ every ounce of your energy to work on
this "Mu." If you hold on without interruption, behold: a
single spark, and the holy candle is lit!
* That is, do not analyze the wato intellectually, giving rise to dualistic concepts by trying to puzzle out its "meaning".