A mendicant goes to a quiet place—a wilderness, the root of a tree, or an empty hut. There, they sit down cross-legged, straighten their body, and establish mindfulness before them.
This scene—a mendicant withdrawn to the forest—shows that this practice unfolds within the broader context of the Gradual Training.

1.With mindfulness, they breathe in; with mindfulness, they breathe out.

This is the most fundamental instruction in meditation. Notice that the Buddha does not say,
“concentrate on the breath” as an object, but rather “breathing” as an activity to which
mindfulness is applied. The stages of breath meditation are not meant to be forced or performed deliberately, but to be observed and understood as the natural deepening of the meditative process.

2.When breathing in heavily, they know, “I’m breathing in heavily.”

When breathing out heavily, they know, “I’m breathing out heavily.”
At first, the breath is coarse and rough. The Pali idiom uses “long” and “short” for these
qualities, but in English, “heavy” and “light” better convey the sense of the breath’s changing
texture.

When breathing in lightly, they know, “I’m breathing in lightly.”
When breathing out lightly, they know, “I’m breathing out lightly.”
Gradually, the breath becomes subtler and more refined.

They practice thinking, “I will breathe in experiencing the whole body.”
They practice thinking, “I will breathe out experiencing the whole body.”
Here, the term “whole body” (sabbakāya) refers contextually to the entire breath, reflecting the fuller and more continuous awareness that arises with tranquility.

They practice thinking, “I will breathe in stilling the physical process.”
They practice thinking, “I will breathe out stilling the physical process.”
The “physical process” (kāyasaṅkhāraṁ) refers to the breath itself, which may become so gentle that it is nearly imperceptible.

This can be compared to a skilled carpenter or apprentice: when making a deep cut, they know, “I’m making a deep cut,” and when making a shallow cut, they know, “I’m making a shallow cut.” Though the text uses “long” and “short,” in English it is more natural to say “deep” and “shallow,” or “heavy” and “light,” to describe the breath.

Thus, they meditate observing an aspect of the body internally, externally, and both internally
and externally.

“Internally” refers to one’s own body, while “externally” refers to the bodies of others or
physical phenomena outside oneself. This distinction applies broadly in Buddhist meditation,
though its relevance varies. In breath meditation, focus is primarily internal, but when
contemplating, for example, a corpse or the material elements, the external aspect becomes more apparent. Beginning with the sense of “me” inside and “world” outside, this contemplation gradually dissolves that duality, revealing that all phenomena share the same nature.

They meditate observing the body as liable to arise, to pass away, and to both arise and pass
away.

This is the vipassanā (insight or discernment) aspect of meditation—seeing not only the arising and ceasing of phenomena, but also their conditioned nature, their inherent tendency (-dhamma) toward impermanence. The meaning of this is explained. Beyond these passages, vipassanā within satipaṭṭhāna particularly concerns the observation of underlying principles.
Or, mindfulness is established simply to the extent necessary for knowledge and awareness of the body as it is.

They meditate independently, not clinging to anything in the world.