This question makes me very happy and joyful to answer.
Because it is easy to answer with Suttas. Not just one Sutta but a stock phrase found in many Suttas. Not just many Suttas but some of the most important Suttas in the whole Suttapiṭaka. Which ones?
How about Anattalakkhaṇasutta?
(The Discourse on NonSelf)
|59. Ekaṃ samayaṃ bhagavā bārāṇasiyaṃ viharati isipatane migadāye. Tatra kho bhagavā pañcavaggiye bhikkhū āmantesi – ‘‘bhikkhavo’’ti. ‘‘Bhadante’’ti te bhikkhū bhagavato paccassosuṃ. Bhagavā etadavoca –
|‘‘Rūpaṃ, bhikkhave, anattā. Rūpañca hidaṃ, bhikkhave, attā abhavissa, nayidaṃ rūpaṃ ābādhāya saṃvatteyya, labbhetha ca rūpe – ‘evaṃ me rūpaṃ hotu, evaṃ me rūpaṃ mā ahosī’ti. Yasmā ca kho, bhikkhave, rūpaṃ anattā, tasmā rūpaṃ ābādhāya saṃvattati, na ca labbhati rūpe – ‘evaṃ me rūpaṃ hotu, evaṃ me rūpaṃ mā ahosī’’’ti.
- The Characteristic of Not-Self
At one time the Buddha was staying near Benares, in the deer park at Isipatana. There the Buddha addressed the group of five mendicants:
“Venerable sir,” they replied. The Buddha said this:
“Mendicants, form is not-self. For if form were self, it wouldn’t lead to affliction. And you could compel form: ‘May my form be like this! May it not be like that!’ But because form is not-self, it leads to affliction. And you can’t compel form: ‘May my form be like this! May it not be like that!’
I just put the beginning in so you would recognize it… However, it is important to note that one needs to properly contemplate form as nonself. The key stock phrase is called the 11 ways which is stated below. You should pay attention to past-present-future which is represented in the Pāḷi as atīta
‘‘Tasmātiha, bhikkhave, yaṃ kiñci rūpaṃ atītā-nāgatapaccup**pannaṃ** ajjhattaṃ vā bahiddhā vā oḷārikaṃ vā sukhumaṃ vā hīnaṃ vā paṇītaṃ vā yaṃ dūre santike vā, sabbaṃ rūpaṃ – ‘netaṃ mama, nesohamasmi, na meso attā’ti evametaṃ yathābhūtaṃ sammappaññāya daṭṭhabbaṃ.
“So you should truly see any kind of form at all—past, future, or present; internal or external; coarse or fine; inferior or superior; far or near: all form—with right understanding: ‘This is not mine, I am not this, this is not my self.’
Each of these 11 ways can be paired up against the other in a very large matrix of combinations. It is so complex, I cannot figure it out. It is so complex, I asked a Math PhD from CalTech University if he could solve how large this matrix combination is. However, he has no time and has not gotten around to it. It is no trivial task.
Furthermore, this stock phrase is matched up against 5 more factors. These are 5 constituent parts (pañcakhaṇḍa). It is not just 5 plus 11, it is a matrix multiplier and it is a big number. However, some are paired and cannot be evaluated at the same time… such as:
past, present, future
course or fine.
They are opposite qualities paired together.
Now, let’s take a the factor of past. Let’s pair that once with coarse and once again with fine. What does that mean? How does this relate to paṭiccasamuppāda (dependent origination)? Nonself is discovered through paṭiccasamuppāda and we know that because the Sutta mentions: past, present, future. The question you asked arose from my answering about material form arising and passing. I made a funny but true comment about maggots found in the dead body of the meditation yogi’s past life. You asked, how does see past material form like that?
You must believe in past lives if you are Buddhist and you must believe in paṭiccasamuppāda if you are a real Buddhist. I assume this is true, or that you are willing to accept that it is true according to Classical Theravāda.
There are several methods to practically and systematically experience paṭiccasamuppāda. The easiest method is called the 5th method described in the Visuddhimagga (Path to Purification). I think it is called the 5th method because of the 5 causes yielding 5 effects but maybe there is another reason.
(a) There were five causes in the past,
(b) And now there is a fivefold fruit;
(c) There are five causes now as well,
(d) And in the future fivefold fruit. Vsm. p160
5 khaṇḍa you know and we will deal with form as the first khaṇḍa.
In order to do proper paṭiccasamuppāda, you need to span the time frame against a three life model. That three life model is past present future or atītānāgatapaccuppannaṃ found in the Anattalakkhaṇasutta and so many other places (over 250 times in the whole Pāḷi collection).
Paṭiccasamuppāda also has nāmarūpa (mentality and materiality) as one of the links, so that means we must see both nāmarūpa in the past, present and future lives. If one is contemplating the life one is living in today, then the first past life is the past, the present life is the present and the first future life is the future. If one is contemplating the first past life with cause and effect. The second past life is the past, the first past life is the present and the life you live in now, is the future and so forth. It works like a rule slide in the countless lives of saṃsāra.
That is the contemplation of past, present and future as oḷārika (coarse) for time in the 11 ways listed of Anattalakkhaṇasutta. This is actually the suttanta way. The sukhumaṃ (fine) way is associated with more immediate time frames. We can go all the way down to the mind moment level and see that certain mind moments have past, present and future causes and results. Sometimes those past causes are immediate, sometimes those past causes are from a past life with a resultant consciousness, or kamma produced materiality, etc. This is a little more difficult to explain here.
Coarse and fine Fine materiality (rūpa) would be individual coarse and fine rūpa found in a group called kalāpā. Coarse refers to the easier to discern 12 rūpa like the four great elements, etc. and fine materiality refers to the 16 more subtle rūpa. 28 total. These rūpa are which arise and pass away in a group with causes are suitable for vipassana.
So how does one discern past life material form?
One needs to develop concentration. The suttas explain this very well, even The Buddha himself, said that when he was a Bodhisatta, after he attained the 4 jhānas, he then directed his mind towards the past. He was not just talking about when he was a baby or inside the womb. He is talking about past lives. One needs good concentration to see these things. Other yogis can do the same. It can also be done on a pure vipassana level without jhāna, but the detail will be less. Never the less, one needs the light of wisdom to do this as a bare minimum.
Fear and Dread
So evaṃ samāhite citte parisuddhe pariyodāte anaṅgaṇe vigatūpakkilese mudubhūte kammaniye ṭhite āneñjappatte pubbenivāsānussatiñāṇāya cittaṃ abhininnāmesiṃ. So anekavihitaṃ pubbenivāsaṃ anussarāmi,
When my mind had become immersed in samādhi like this—purified, bright, flawless, rid of corruptions, pliable, workable, steady, and imperturbable—I extended it toward recollection of past lives. I recollected many kinds of past lives.
seyyathidaṃ—ekampi jātiṃ dvepi jātiyo tissopi jātiyo catassopi jātiyo pañcapi jātiyo dasapi jātiyo vīsampi jātiyo tiṃsampi jātiyo cattālīsampi jātiyo paññāsampi jātiyo jātisatampi jātisahassampi jātisatasahassampi anekepi saṃvaṭṭakappe anekepi vivaṭṭakappe anekepi saṃvaṭṭavivaṭṭakappe: ‘amutrāsiṃ evaṃnāmo evaṅgotto evaṃvaṇṇo evamāhāro evaṃsukhadukkhappaṭisaṃvedī evamāyupariyanto, so tato cuto amutra udapādiṃ; tatrāpāsiṃ evaṃnāmo evaṅgotto evaṃvaṇṇo evamāhāro evaṃsukhadukkhappaṭisaṃvedī evamāyupariyanto, so tato cuto idhūpapanno’ti. Iti sākāraṃ sauddesaṃ anekavihitaṃ pubbenivāsaṃ anussarāmi.
That is: one, two, three, four, five, ten, twenty, thirty, forty, fifty, a hundred, a thousand, a hundred thousand rebirths; many eons of the world contracting, many eons of the world expanding, many eons of the world contracting and expanding. I remembered: ‘There, I was named this, my clan was that, I looked like this, and that was my food. This was how I felt pleasure and pain, and that was how my life ended. When I passed away from that place I was reborn somewhere else. There, too, I was named this, my clan was that, I looked like this, and that was my food. This was how I felt pleasure and pain, and that was how my life ended. When I passed away from that place I was reborn here.’ And so I recollected my many kinds of past lives, with features and details.
So to answer your question of how. You need to develop concentration, preferably all the way to the fourth jhāna and then direct your mind towards mind and matter and then the past lives. After that you will see the features and details of materiality.