Whenever a mendicant practices breathing while experiencing the mind, or gladdening the mind, or immersing the mind in samādhi, or freeing the mind—at that time they meditate observing an aspect of the mind—keen, aware, and mindful, rid of covetousness and displeasure for the world. There is no development of mindfulness of breathing for someone who is unmindful and lacks awareness, I say. That’s why at that time a mendicant is meditating by observing an aspect of the mind—keen, aware, and mindful, rid of covetousness and displeasure for the world.

Whenever a mendicant practices breathing while observing impermanence, or observing fading away, or observing cessation, or observing letting go—at that time they meditate observing an aspect of principles—keen, aware, and mindful, rid of covetousness and displeasure for the world. Having seen with wisdom the giving up of covetousness and displeasure, they watch over closely with equanimity. That’s why at that time a mendicant is meditating by observing an aspect of principles—keen, aware, and mindful, rid of covetousness and displeasure for the world.

That’s how mindfulness of breathing, when developed and cultivated, fulfills the four kinds of mindfulness meditation.