Logic cannot reveal the truth or prove anything. Logical operations are applied to propositions to produce inferences. A proposition is a statement about something. In practice, logical operations are always applied in the context of a worldview. One’s worldview consists of propositions that are considered axiomatically true. An axiomatic truth is one that is not amenable to logical analysis and cannot therefore be tested by the application of logic. Axioms are beliefs about the world that exist prior to the application of logic and are used to validate inferences. And, nota bene, a belief is a feeling about an idea.
In any logical analysis, the validation of an inference consists of comparing it to one’s beliefs. We judge something to be “true” if it is consistent with our existing beliefs, and untrue if it is inconsistent.
“Truth” in this sense is relative to a body of beliefs that are tautologically defined as true and at the same time treated as the definition of truth. P is true because P is considered to be true. Any conclusion that appears to be consistent with one’s worldview is judged to be valid and any conclusion that conflicts with one’s worldview is considered invalid. The weak point of any logical inference is always in the axioms that make it seem plausible/implausible.
Truth cannot be arrived at by logic. Nāgārjuna did not demonstrate that “The agent cannot be the same nor different from the consumer of the action”. What he did was assert that this deductive inference was consistent with what he already considered to be true.
Nāgārjuna himself never analyses his own beliefs. He never talks about his a priori views. And those who study him keep up this tradition. No one enquires into the details Nāgārjuna’s worldview or is able to state what he considered axiomatic. And no one seems to notice that no matter what the topic, his conclusions are always the same: X doesn’t exist; X & Y are not different.
One might want to ask, for example, under what conditions–i.e., given which axioms–does nirvāṇa seem to be identical to saṃsāra? Or, to be more explicit: in what worldview is not being reborn exactly the same as being reborn? Apart from the fact that this violates the logical principle of noncontradiction (and thus amounts to trivialism), this is not a proposition that any early Buddhist would have accepted as valid, since it very obviously destroys the foundations of Buddhist soteriology.
To make this more topical, this means that Nāgārjuna’s solution to the problem of action at a temporal distance is the least helpful of the bunch. Asked “how do we connection actions to consequences without violating dependent arising,” Nāgārjuna responds “Actions don’t exist and consequences don’t exist” (see the end of Chapter 17 of MMK).
As far as I can see Nāgārjuna makes sense if and only if he accepted particular axioms, notably: “there is a state in which sensory experience is absent; and that state is reality.” In the background he also redefined svabhāva and used it as a straw man: where Buddhists defined it phenomenologically as sui generis (being identifiable), Nāgārjuna redefined it metaphysically as autopoiesis (being self-creating).
If you start with these axioms and some basic Buddhist doctrine, it’s relatively easy reproduce Nāgārjuna’s conclusions via deduction. This doesn’t “demonstrate” anything except the age old weaknesses of logic.
Your complaints about my account of the problem of action at a temporal distance don’t address the substance of the idea. For example, I don’t say that it happened overnight. I agree that the various responses to this problem took time to emerge. But the idea that no one was responding to this problem is flatly wrong. We can be sure about this because both the Buddhists who proposed the pudgalavāda and sarvāstivāda responses tell us that they were responding to exactly this problem.
Those who propose some variety of kṣanavāda are less open about why they abandoned Buddhavacana for this innovative doctrine, but it fits the pattern of the other innovations that occurred around the same time.
Nor do I argue that this was the only driver of change. I have only ever said that this was a driver of change. Your alternative explanation “they were trying to make sense of the Buddha teachings” really has no explanatory power at all because it is too vague. And it doesn’t exclude them trying to make sense of those teachings in exactly the way that pudgalavādins and sarvāstivādins tell us that they were trying to make sense of them.
Which is to say, you’re not arguing against me, since I was just reporting what ancient Buddhists said about what they thought they were doing (all I did was extrapolate from that to include kṣanavāda). Rather you are arguing against the descriptions of the process left to us by actual Buddhists who were engaged in the process at the time.