What is the difference between satipaṭṭhāna and ānāpānasati?

Yesterday, while reading MN62 The Longer Advice to Rāhula, I came to this understanding that ānāpānasati is a practice to see non-self in the five aggregates.

This sutta starts with the Buddha admonishing Rāhula, urging him to see the five aggregates as ‘This is not mine, I am not this, this is not my self.’ Later, Sāriputta suggested ānāpānasati and then Rāhula asked Buddha for an exposition.

Before giving the usual four tetrad, 16 steps ānāpānasati formula, Buddha taught the following six groupings of meditation themes:

  1. Contemplate non-self and detachment from five elements (earth, water, fire, air, space)
  2. Meditate like the earth, water, fire, wind, space so that pleasant and unpleasant contacts will not occupy the mind.
  3. Meditate on Brahma vihara (metta, karuna, mudita, uppekkha).
  4. Meditate on loathsomeness.
  5. Meditate on impermanence.

In the past, I would assume that those were the preliminaries of ānāpānasati. Yesterday, however, I thought to myself what if they were actually ānāpānasati practice proper? Suddenly, I saw ānāpānasati in a totally different light. Before going further, I need to first clarify my interpretation of an important term sankhara in the fourth and eighth steps of ānāpānasati below.

There were many interpretations of what bodily and mental formations (kaya and citta sankhara) meant in the fourth and eighth steps of ānāpānasati. In the Agama SA57, there was a phrase “于色见是我,若见我者,是名为行” meaning Buddha term sankhara as one who sees a Self in form and the other four aggregates. Therefore, kaya and citta sankhara could mean fabricating a Self view in the body and mental processes (feeling, perception and volition).

With this interpretation, the first meditation theme of contemplating the five elements could be seen as a method to calm bodily fabrication in the fourth step of ānāpānasati. The second theme of meditating like 5 elements prevents pleasant and unpleasant contacts from occupying the mind. Since contact brings about mental processes (feeling, perception and volition), mental fabrications mentioned in the eighth step can be calmed.

The third theme of meditating on Brahma vihara gladden and still the mind in the tenth and eleventh steps. Finally, the last two themes of meditating on loathsomeness and impermanence liberates the mind from lust and conceit in the twelfth step.

Thereafter, the fourth tetrad becomes undirected, observing all mental phenomena that arise as impermanence, fading away and ceasing. Thereby letting go of the notion of self in the five aggregates.

Lastly, the Buddha concluded that “even when the final breaths in and out cease, they are known, not unknown”. It suggests that breathing is to be used as an anchor to remind oneself of the practice above continuously.

I find that with this interpretation and understanding, the 16 steps of ānāpānasati fall into place nicely.