I am currently reading your thesis, The Dark Side of Dharma- Why have adverse effects of meditation been ignored in contemporary Western secular contexts, and I’ve arrived at your characterization of the relationship between concentration and insight:
Concentration (or calm abiding) practices (Pali: samatha) are generally regarded as preliminary meditations that calm and stabilise the mind. However, unlike in Western contemporary applications, calmness is not cultivated as an end in itself, but rather as preparation for insight meditation practice (Pali: vipassana). When the mind has achieved a requisite degree of stable concentration, the individual is able to pay close enough attention to moment-to-moment mental occurrences to see into their true nature, which is the basis of vipassana, or ‘penetrating insight’ practice.
I’ve read the first four Nikayas (thanks, Pali Text Society!), and although later authors and commentators may have claimed a distinction between the practice of concentration and the attainment of wisdom, I didn’t come across such.
I have an overview of the early teaching here: https://zenmudra.com/post-the-early-record-anm/
Gautama reported transcending the last of the states of concentration, or attaining the final state of concentration (I think he asserts both), through “lack of desire”, and arriving at a state absent the “cankers” of desire, becoming, and ignorance. All the states of concentration hinge on the cessation of action through “determinate thought”, and the final state is characterized as the cessation of “perceiving and feeling” (so, determinate thought in perceiving and feeling). He says this:
And again … a good [person], by passing quite beyond the plane of neither-perception-nor-non-perception, enters on and abides in the stopping of perception and feeling; and when [such a person] has seen by means of wisdom [their] cankers are caused to be destroyed. And… this [person] does not imagine [his or her self] to be aught or anywhere or in anything.
(MN III 42-45, Pali Text Society Vol III pg 92-94)
What such a person sees is described as:
…[an individual] comprehend[s] thus, ‘This concentration of mind … is effected and thought out. But whatever is effected and thought out, that is impermanent, it is liable to stopping.’ When [the individual] knows this thus, sees this thus, [their] mind is freed from the canker of sense-pleasures and [their] mind is freed from the canker of becoming and [their] mind is freed from the canker of ignorance. In freedom is the knowledge that [one] is freed and [one] comprehends: “Destroyed is birth, brought to a close the (holy)-faring, done is what was to be done, there is no more of being such or so’. [They] comprehend thus: “The disturbances there might be resulting from the canker of sense-pleasures do not exist here; the disturbances there might be resulting from the canker of becoming do not exist here; the disturbances there might be resulting from the canker of ignorance do not exist here. And there is only this degree of disturbance, that is to say the six sensory fields that, conditioned by life, are grounded on this body itself.”
(MN III 108-109, Pali Text Society Vol III pg 151-152)
As you can see, the wisdom (the comprehension) is a consequence of the attainment of the cessation of determinate thought in perceiving and feeling. There is no separate insight meditation practice.
The Gautamid characterized suffering as a consequence of ignorance, of willful activity, and of the subsequent stationing of consciousness (SN II 65 “Kindred Sayings on Cause” XII, 4, chapter 38 “Will”, Pali Text Society vol. 2 pg 45). His insight I believe was a result of his attainment of that final stage of concentration (or his transcendence of it), where determinate thought in action of speech, of body, and of mind (“perceiving and feeling”) ceases. What passes for enlightenment since Gautama is mostly the attainment of the cessation of action of the body, a part of the way of living of Gautama and an attainment conducive to reflection on “latent conceits that ‘I am the doer, mine is doer’ with regard to this consciousness-informed body” (MN III 18-19, Pali Text Society III pg 68), but in my understanding not the attainment that gives rise to insight regarding ignorance, willful activity, and suffering.
Good luck with your continued research and your writing.