When I first became introduced to Buddhism, as per the traditional interpretation, I was taught that all the discourses stem from the historical Buddha. Among careful reading of the suttas, there appeared to be variations and divergences as to what is required for liberation. Needless to say I was overwhelmed by what others and myself deemed inconsistencies. It felt impossible that all these discourses could logically stem back to a single author.
If the tradition view that all goes back to the Buddha was the case, (therigatha and theragatha aside) that would mean that every single bhikkhu of the tens of thousands of bhikkhus that ever lived during the 500 period prior to the dhamma being put to writing never invented or preserved a word/teaching of their own, including those chief bhikkhus that Gotama tasked with teaching the dhamma in his place as he got older (Sariputta, Ananda, etc.). The idea that no offered their own vows, rules, theses or ideas, expansions or brought with them previous assumptions or beliefs, or contributed to the religious conversation over the decades upon decades that spans a half millennia, that I find that, highly highly unlikely. One thing that is taught is that Bhikkhus never stopped authoring and composing suttas, even a thousand of years after Gotama’s death, new suttas were emerging and being claimed as the official, authentic words of the Buddha.
Of course, Gotama the Buddha was very likely a historical figure set in a very specific environment of Greater Magadha at a certain time, and much like other historical figures [Jesus of Nazareth, Zarathustra] they each did inspire a philosophy and movement so there must be a root teaching or teachings among the material. However, from the study of these religions, we know they take on elements of their own following their teacher’s deaths, often leading to increased superstition and supernaturalism. A second feature is the stressing of the church/collective over that of the individual.
For an example of this, compare the Jesus of Nazareth from the Gospel of Mark (70 AD) to the Jesus of Nazareth from the Gospel of John (110-120 AD). In the former, he is a prophet who doubts himself, suffers in loneliness, and feels very much like a human figure who struggles with the task his God has handed him. Then some 40-50 years, in the Gospel of John, he is presented as the omniscient, infallible alpha and omega who has existed before the dawn of time and is equal to God and is a part of God. The teachings in the Gospel of John also look considerably different than the those in the earlier Mark, with the Gospel of John stressing faith as a sotierological mechanism and belief more while the latter stressing good works.
We see this in Buddhism too, with the Buddha being given powers or interacting with devas and demons, who I suspect we would have caught onto if they were frequent visitors to this Earth… if you catch my drift.
One example of an evolution in Buddhism is the idea of refuge. We find suttas with a single refuge, some with two, and some with three. The initial/original refuge was likely oneself, metaphorically speaking, and we have Gotama saying that one should have no other refuge other than this. Then we have things like refuge in the triple gems, which contradicts Gotama’s earlier statement. It’s very clear to me that refuge in the triple gems was an evolution that took place after Gotama’s death, is not authentic early buddhism, but has become the unquestioned mainstream. Of course since evolutions are gradual, there was likely a time period of dual refuge, and I suspect the oneself got replaced with the Buddha and the dharma, and later the Sangha was also added.
Funny enough, something similar happened in Christianity. Jesus asked his followers not to pray collectively in public or the synagogues like the pharisees did, but rather to pray in private, alone. What do most Christians do today? They go to churches were they all stand and pray collectively, the exact opposite of what their teacher taught.
But back to the historical Buddha. Perusing the suttas, many researchers have put forth an effort to discern and decipher what is earlier and what is later material among the texts we call EBTs, and to identify and explain contradictions when they are found. There are various methods and ideas to conduct this which go beyond the scope of this response. It’s an evolving field, because with up and coming translations of Agamas and other non-Therevada EBT texts, we can attempt to reconstruct (lost) root texts, and identify if suttas were modified to reflect the sectarian beliefs of the 18 schools they are affiliated with. Ie, for example we know the pudgalavadins had a Sutta pitaka, and although lost, it is very likely that they had suttas that depicted Gotama as teaching the existence of a pudgala, thus confirming their sectarian views. Did the historical Gotama likely teach about pudgalas? Probably not, but if the Pudgala sutta pitaka had survived in place of Therevada’s, most of us here would think he did.
But even within an extant canon, like that of Therevada we encounter historical contradictions.
One example of a contradiction was a sutta or two where the Buddha recommends or describes a meditation practice that (we know from other sources) the Jains practiced. The way that meditation is described, in some other suttas, that very same meditation style is censured and criticized by the Buddha. What is correct? It seems very unlikely Gotama would recommend a jain practice, so what is most likely is that Jain converts to the Sangha, during or after the Buddha’s death maintained some of their practices and ascribed it to Gotama, and it got preserved in sutta. This wouldn’t be the only case of stuff like this happening… there are many cases of inter-sutta contradictions, which are sufficiently explained by viewing the suttas as a non-heterogenous collection composed over several centuries, but with stratums that are capable of being identified.
Historically, we can infer that numerous members of the early sangha believed in literal rebirth. This is not a controversial view, as it was a common belief at the time among seekers. The controversy arises of what Gotama believed or stressed, because we have suttas where Gotama appears concerned about metaphysics, doctrines, the past, and ones where he shies away from these inquires and claims not to profess anything. We have suttas that present Gotama as extremely quiet, very hesitant to talk or utter a word, and suttas that portray him as a wise teacher who has a billion things to say.
At the end of the day, what you believe the historical Gotama taught boils down to which EBTs you identify as being part of the early stratum and thus the authentic teachings and which belong to a later ones. There is a massive spectrum between those who claim all goes back to the Buddha and those who claim none of the surviving material could be reliably dated to the historical Buddha. Most scholars find themselves in various points along the middle between these two, highly unlikely extremes.
I’m positive that a psychological interpretation of rebirth, focused on ending I/me-making, identity view, and the quenching of the generation of a self was part of early buddhism. In my practice, it has proven quite helpful.
I hold the view that it is certainly possible that literal rebirth was a part of early buddhism, but there are too many inconsistencies between texts to (imo) currently decipher the original mechanism/model of rebirth (if any).
For example, there are suttas which suggest that the collective past karma determines rebirth and suttas where only one’s final mindstate determines rebirth. There are also suttas that speak of rebirth ending when one simply doesn’t want or grasp after a new body after death, with no mention to karma playing a role at all. There are suttas that describe as all actions contributing to karma, while others that only indicate intentional and not accidental actions contributing to karma.
Too many inconsistencies for the critical observer, but just enough to inspire optimistic curiosity. Of course, one can wholeheartedly attempt to defend the traditional Therevada interpretation via a careful exegesis by which one aims to demonstrate that these inconsistencies are anything but. Sujato and Analayo bhikkhus are involved in this area. As scholars, while I find some of their arguments truly convincing, in other cases, it is apparent to me the contradictions and inconsistencies can’t be explained away.