Fukanzazengi IV: 'Posture' etc.

Master Gudo Nishijima sitting zazen.

In the next section, Master Dogen reiterates that zazen is not a willful mental effort of the sort that intentionally thinking something or willing something is. He advises we give everything ('the myriad things') a rest and to stop thinking of things in terms of them being 'good' and 'bad' (i.e. to let them arise just as they are). We should not try to become a buddha; to do so would just be to engage in a type of misguided willful thinking based on whatever we imagine a 'buddha' to be:

"In general, a quiet room is good for practicing [za]zen, and food and drink
are taken in moderation. Cast aside all involvements. Give the myriad things a
rest. Do not think of good and bad. Do not consider right and wrong. Stop the
driving movement of mind, will, consciousness. Cease intellectual consideration
through images, thoughts, and reflections. Do not aim to become a buddha.
How could [this] be connected with sitting or lying down?"

'How could [this] be connected with sitting or lying down?' Here Master Dogen is emphasising that zazen is not just the usual activity of sitting or lying down where we might be daydreaming or thinking as we habitually do. Zazen is quite different in that it requires us to just stop doing our habitual thinking activity when we notice that we are doing it.

The instructions continue with a description of the physical posture of zazen:

"We usually spread a thick mat on the place where we sit, and use a round
cushion on top of that. Either sit in the full lotus posture or sit in the half lotus
posture. To sit in the full lotus posture, first put the right foot on the left thigh,
then put the left foot on the right thigh. To sit in the half lotus posture, just press
the left foot onto the right thigh."

Most people will initially find it difficult to sit in half lotus as advised here. In fact, you might even hurt yourself if you try. People who have been doing yoga for some time may be able to attempt these postures, but everyone should be careful when attempting this; if there is any pain at all (particularly in the knees) then please stop. The hips will generally loosen up if you practice every day. You might consider doing a few warm-up stretches. Progress will likely happen quite slowly though, so patience is required. What's called the Burmese posture is a safer alternative in the meantime. It's a good one because the knees are both on the floor forming the very stable base that both lotus and half lotus provide.

The hand position discussed below is called the 'mudra'. It's said the thumbs should touch together gently; sometimes we might find that we're pushing them together too hard and so we can relax this or maybe we'll notice that our thumb tips have fallen apart or collapsed downwards in which case we should just fix them.
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"Spread the clothing loosely and make it neat. Then put the right hand above
the left foot, and place the left hand on the right palm. The thumbs meet and
support each other. Just make the body upright and sit up straight. Do not lean
to the left, incline to the right, slouch forward, or lean backward. The ears must
be aligned with the shoulders, and the nose aligned with the navel. Hold the
tongue against the palate, keep the lips and teeth closed, and keep the eyes open.
Breathe softly through the nose."
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We sit upright and gently keep the mouth and teeth closed while we breathe gently and normally through the nose. The tongue is kept against the roof of the mouth behind the front teeth. This stops air from going over the taste buds causing salivation. The eyes are generally kept relaxed and half open with the gaze cast down at about a 45 degree angle.