Awhile ago when I was searching for information on ānāpāna within the āgamas, I was grepping away as usual, and I saw that with just one exception (SA 746), references to ānāpāna were found in just one fascicle of the text, and even within just one group of texts, SA 801-815.
At this point I started to become curious. What does this mean about the compilation of the Saṃyukta Āgama? I still don’t know, but at least ānāpānasmṛti had its own saṃyukta, and a place within the sūtra aṅga, so it must have been fairly early and considered a major practice by at least some people in the community.
Then I got to the (probably late) SA 809, which is warning about impurity meditations and instead advising ānāpāna. So I thought, are impurity meditations even taught in the Saṃyukta Āgama? They certainly have no saṃyukta (as ānāpāna has). So I searched around, and while there are a few scattered sūtras, it looks like they were either late additions or extremely marginal. The fullest treatment of these practices is in SA 1165, which is in the saṃyukta for the Six Entrances.
What about the Brahmavihāras? I searched through the Saṃyukta Āgama, and found exactly five instances, all repetitions of the same stock formula of spiritual accomplishments:
… first dhyāna, second dhyāna, third dhyāna, fourth dhyāna; kindness, compassion, joy, abandoning; the realm of infinite space, the realm of infinite consciousness, the realm of nothingness, the realm of neither perception nor non-perception…
Nowhere in the Saṃyukta Āgama (to the best of my knowledge) is anyone advised to practice them, or taught how to practice them, or anything about their benefits. Kindness (慈) and compassion (悲) are very widely found throughout the collection, but not in the list of practices that form the Brahmavihāras (慈、悲、喜、捨). There are also no references to “Four Brahmavihāras,” i.e. “四梵住” and “brahmavihāra” (梵住) appears only as a synonym for “noble abiding” and “divine abiding.”
Meditation on the elements? While the elements appear frequently throughout the SA, when it comes to meditation we are mainly just told not to grasp them.
Then there is the list of four practices to cultivate. For example, ānāpāna to sever thoughts, meditation on impurity to sever desires, etc. This list is found only one time, in SA 815, so it is likely not part of the original collection. The lone statement that ānāpāna is cultivated to sever thoughts, however, is found quite frequently throughout SA 801-815.
Meditation on the thirty-two marks of the Buddha is not found in the SA either (no big surprise). In fact the Buddha does not appear to have thirty-two marks in this collection.
So with all of this, we might ask: what meditations can we know were actually important and central within the Saṃyukta Āgama at the time of its compilation? From what I have seen so far, it appears that abstract meditations on the skandhas, etc., as impermanent, suffering, empty, not self, etc., were very important.
The Four Bases of Mindfulness are also referenced very frequently throughout the text. For meditation, the two most referenced frameworks appear to be the Four Bases of Mindfulness and the Seven Factors of Bodhi. The Bodhi factor of “mindfulness” is also canonically defined to be the Four Bases of Mindfulness.
But taking the above into account, these Four Bases of Mindfulness would probably be more like those in SA 605-639, not like those very elaborate formulations in the Satipaṭṭhāna Sutta, in which an entire host of other practices are made to conform to, and fulfill, the Four Bases of Mindfulness.