The word "satipatthana" is the name for an approach to meditation aimed at establishing sati, or mindfulness. The term sati is related to the verb sarati, to remember or to keep in mind. It is sometimes translated as non-reactive awareness, free from agendas, simply present with whatever arises, but the formula for satipatthana doesn't support that translation. Non-reactive awareness is actually an aspect of equanimity, a quality fostered in the course of satipatthana. The activity of satipatthana, however, definitely has a motivating agenda: the desire for Awakening, which is classed not as a cause of suffering, but as part of the path to its ending (see SN 51.15). The role of mindfulness is to keep the mind properly grounded in the present moment in a way that will keep it on the path. To make an analogy, Awakening is like a mountain on the horizon, the destination to which you are driving a car. Mindfulness is what remembers to keep attention focused on the road to the mountain, rather than letting it stay focused on glimpses of the mountain or get distracted by other paths leading away from the road.

As a compound term, satipatthana can be broken down in two ways, either as sati-patthana, foundation of mindfulness; or as sati-upatthana, establishing of mindfulness. Scholars debate as to which is the proper interpretation, but in practice both provide useful food for thought.

The first interpretation focuses on the objects of the meditation practice, the focal points that provide mindfulness with a foundation — or, to use the more idiomatic English phrase adopted here, a frame of reference. Altogether there are four: the body in and of itself; feelings in and of themselves; mind in and of itself; and mental qualities in and of themselves. The "in and of itself" here is crucial. In the case of the body, for instance, it means viewing the body on its own terms rather than in terms of its function in the context of the world (for in that case the world would be the frame of reference). Dropping any concern for how the body's beauty, agility, or strength fits into the world, the meditator simply stays with the direct experience of its breathing, its movements, its postures, its elementary properties, and its inevitable decay. A similar principle applies to the other foundations of mindfulness.

The second interpretation of satipatthana — sati-upatthana — focuses on the process of the meditation practice, on how a frame of reference is established. This sutta gives three stages for this process, applied to each frame of reference. The first stage, as applied to the body, is this:

The monk remains focused on the body in and of itself — ardent, alert, and mindful — putting aside greed and distress with reference to the world.

"Remaining focused" refers to the element of concentration in the practice, as the meditator holds to one particular frame of reference amid the conflicting currents of experience. "Ardent" refers to the effort put into the practice, trying to abandon unskillful states of mind and develop skillful ones in their stead, all the while trying to discern the difference between the two. "Alert" means being clearly aware of what is happening in the present. "Mindful," as mentioned above, means being able to keep the frame of reference continually in mind. As these qualities work together, they bring the mind to a solid state of concentration. Although satipatthana practice is often said to be separate from the practice of jhana, a number of suttas — such as MN 125 and AN 8.63 — equate the successful completion of this first stage with the attainment of the first level of jhana. This point is confirmed by the many suttas — MN 118 among them — describing how the practice of satipatthana brings to completion the factors for Awakening, which coincide with the factors of jhana.

The second stage of satipatthana practice is this:

One remains focused on the phenomenon of origination with regard to the body, on the phenomenon of passing away with regard to the body, or on the phenomenon of origination & passing away with regard to the body.

The "phenomena of origination and passing away" covers events either directly or indirectly related to one's chosen frame of reference. "Directly" means changes in the frame of reference itself. For instance, when focused on the body, one may notice the arising and passing away of breath sensations within it. "Indirectly," here, means events in any of the other three foundations of mindfulness as they relate to the body. For example, one might notice the arising and passing away of feelings of pleasure or mental states of irritation in connection to events in the body. Or one might notice lapses of mindfulness in one's focus on the body.

In each of these cases, if the origination and passing away is of neutral events such as the aggregates, one is directed simply to be aware of them as events, and to let them follow their natural course so as to see what factors accompany them and lead to their comings and goings. However, when skillful or unskillful mental qualities — such as the factors for Awakening or the Hindrances — arise and pass away, one is encouraged to foster the factors that strengthen jhana and eliminate the factors that weaken it. This means actively getting engaged in maximizing skillful mental qualities and minimizing unskillful ones. One thus develops insight into the process of origination and passing away by taking an active and sensitive role in the process, just as you learn about eggs by trying to cook with them, gathering experience from your successes and failures in attempting increasingly difficult dishes.

As this process leads to stronger and more refined states of concentration, it makes one sensitive to the fact that the grosser one's participation in the process of origination and passing away in the mind, the grosser the level of stress that results. This leads one to let go of increasingly refined levels of participation as one is able to detect them, leading to the third and final stage in satipatthana practice:

Or his mindfulness that 'There is a body (feeling, mind, mental quality)' is maintained [simply] to the extent of knowledge & recollection. And he remains independent, not clinging to anything in the world.

This stage corresponds to a mode of perception that the Buddha in MN 121 terms "entry into emptiness":

Thus he regards it [this mode of perception] as empty of whatever is not there. Whatever remains, he discerns as present: "there is this."

This is the culminating equipoise where the path of the practice opens to a state of non-fashioning and from there to the fruit of Awakening and release.

At first glance, the four foundations of mindfulness for satipatthana practice sound like four different meditation exercises, but MN 118 makes clear that they can all center on a single practice: keeping the breath in mind. When the mind is with the breath, all four foundations of mindfulness are right there. The difference lies simply in the subtlety of one's focus. It's like learning to play the piano. As you get more proficient at playing, you also become sensitive in listening to ever more subtle levels in the music. This allows you to play even more skillfully. In the same way, as a meditator gets more skilled in staying with the breath, the practice of satipatthana gives greater sensitivity in peeling away ever more subtle layers of participation in the present moment until nothing is left standing in the way of total release.