For sanzen (zazen), a quiet room is suitable. Eat and drink moderately. Cast aside all involvements and cease all affairs. Do not think good or bad. Do not administer pros and cons. Cease all the movements of the conscious mind, the gauging of all thoughts and views. Have no designs on becoming a Buddha. Sanzen has nothing whatever to do with sitting or lying down.
At the site of your regular sitting, spread out thick matting and place a cushion above it. Sit either in the full-lotus or half-lotus position. In the full-lotus position, you first place your right foot on your left thigh and your left foot on your right thigh. In the half-lotus, you simply press your left foot against your right thigh. You should have your robes and belt loosely bound and arranged in order. Then place your right hand on your left leg and your left palm (facing upwards) on your right palm, thumb-tips touching. Thus sit upright in correct bodily posture, neither inclining to the left nor to the right, neither leaning forward nor backward. Be sure your ears are on a plane with your shoulders and your nose in line with your navel. Place your tongue against the front roof of your mouth, with teeth and lips both shut. Your eyes should always remain open, and you should breathe gently through your nose.
Cast aside all involvements and cease all affairs.
This just means that when we are preparing to do zazen, we should deliberately set aside our concerns and thinking about the past and future. A Theravadan monk I sit with sometimes says that we carry around two heavy bags - one called 'past' and one called 'future'. When we prepare to meditate we put these down.
Do not think good or bad. Do not administer pros and cons. Cease all the movements of the conscious mind, the gauging of all thoughts and views.
What this means is that we should not judge our experience. This is easier said than done of course, especially when language like 'do not...' is used, as this might easily lead one to react to one's judgement as 'bad' and idealise non-judging as 'good'.
Learning to be patient, compassionate and non-judgmental is fundamental to any kind of 'mindfulness'-type meditation, including Shikantaza. The mind is always 'doing', always trying to acheive something, get something or get away from something else. In zazen we are finding a way to enter a different mode, a mode of 'being' where we are just open to our experiences as they are. If something we don't like happens we just notice it, if a judgement occurs, we just notice that - rather than adding fuel to the fire by judging our judgement. This way, the mind gradually settles down by itself.
Sometimes the metaphor of muddy water is used to describe the mind in meditation. We can't get the mud to go to the bottom by forcing it down, that would just stir up more mud. Instead we stop trying to make it subject to our will. We leave it alone and in the light of awareness it settles down by itself.
Have no designs on becoming a Buddha.
There is a tendency in modern commentary on Soto Zen, that Zen practice is about not having goals. People even seem to set up abandoning goals as a sort of goal or become quite judgemental about the idea of any sort of intention or to deny the existence of their own motivations. And they cite Dogen in support of this idea. I suspect that this is a misunderstanding.
We would not take up and remain on the Zen path if it was not our intention to abandon delusion, craving and aversion. Is that not having 'designs on becoming a Buddha'? Did not Dogen himself take up the Zen path to become free from the realm of birth, death and suffering? Did he not voyage to Korea and China and visit the wisest masters he could find in order to clear his doubt and confusion? I don't think that he is suggesting here that we shouldn't seek the way with equal vigour.
It is interesting to note here that his instruction to not seek enlightenment is not a general statement, but is in reference specifically to zazen instruction. It is indeed true that for Shikantaza or any kind of mindfulness-type meditation, simply being present with one's experience rather than striving to have a different kind of experience is essential. On the other hand we still need to have the intention to sit with our experiences, to remain in the present moment and to return our attention to the present moment when it wanders.
Sanzen has nothing whatever to do with sitting or lying down.
Another preoccupation of some Soto commentators is posture. Some even go so far as to suggest that posture is the whole of Zen, that correct posture is itself enlightenment. Again I think this is a misunderstanding.
Good posture is important. And Dogen follows with the details of what good posture is from the perspective of traditional Zen. But posture is not the only thing. I could sit daydreaming in a perfect lotus posture for hours, but that would not be 'good zazen'.
It is true that Zazen is not a 'mind-only' practice. We practice with the body; we practice with the mind; we practice with the universe. It is the body-mind-universe that practices. Practicing with the body does mean having a posture that helps us to be awake. But even more importantly it means not separating the mind from the body in whatever we are doing - whether we are driving, cooking, lying down or doing zazen. It means keeping the attention on the body and our activity rather than cutting it off and getting lost in abstractions. The Buddha taught meditation in four postures: sitting, standing, walking and lying down.
There is little that the body can do to keep the mind from separating itself off into a world of delusion. The body is always the body. It is the mind that becomes deluded. And it is the mind that has the opportunity to return to body-mind samadhi.
Personally speaking, I usually sit in the lotus position, however I've also sat in half-lotus, seiza and on a chair. Any differences in these postures with regards to zazen must be very subtle as I don't really notice a difference. The only posture I really have trouble with is lying down as I tend to fall asleep.
There is another meaning which may apply to Sanzen has nothing whatever to do with sitting or lying down. The mind of Zen moves freely without getting attached anywhere. It doesn't get stuck on postures or zazen and not-zazen; it doesn't exclude anything. In the Platform Sutra, the Sixth Patriarch, Master Eno says:
One Practice Samadhi means at all times, whether walking, standing, sitting, or lying down, always practicing with a straightforward mind. The Vimalakirti Sutra says, 'A straightforward mind is the place of enlightenment,' and 'a straightforward mind is the pure land.' ...Deluded people who cling to the external attributes of a dharma get hold of One Practice Samadhi and just say that sitting motionless, eliminating delusions, and not thinking thoughts are One Practice Samadhi. But if that were true, a dharma like that would be the same as lifelessness and would constitute an obstruction of the Way instead. The Way has to flow freely. Why block it up? The Way flows freely when the mind doesn't dwell on any dharma. Once it dwells on something, it becomes bound. If sitting motionless were right, Vimalakirti wouldn't have criticized Shariputra for meditating in the forest.
Good friends, I know there are people who tell others to devote themselves to sitting and contemplating their minds or purity and not to move or to think. Deluded people are unaware, so they turn things upside down with their attachments. There are hundreds of such people who teach the Way like this. But they are, you should know, greatly mistaken.
This is the expansive mind of Zen that doesn't cling to anything, not to sitting, lying down, zen nor worldly things. Rather it is a mind that is excludes nothing and is intimate with everything; the space that includes all phenomena and the phenomena themselves. Of course, we usually need to practice in order to realise it - which probably means sitting meditation.