... And if we can't find any such stable advances: What explanation can we give?

This may or may not address your question. Forgive me if not; I'm not sure I understand why you're seeking only justification with respect to 'established insights'. But if you'll follow me here in understanding philosophy as that discipline examining questions many find important but which do not yet have agreed upon methods to generate answers, then progress is - I think - apparent.

Most of what we call science was first considered philosophy. For example, physics used to be a philosophical enterprise, until methods for generating answers to questions concerning, say, celestial mechanics, reached consensus, after which physics emerged as a scientific discipline.

More recently, a similar emergence occurred for fields like linguistics and psychology. Indeed, in many of his early writings Chomsky, for example, is engaged in disputes with philosophers such as Hilary Putnam, rather than names you might recognize from linguistics.

Even more recently, the field of applied ontology has emerged at the intersection of metaphysics, data engineering, and formal logic (two of which are often classified as philosophy), and a growing number of philosophers are moving to fill consulting roles in industry and research as field develops.

I feel I could go on, but I hope this goes some way in providing the justification you're seeking.

Dear John Beverley,

This does address my question, of course, and thanks for your answer! In fact, I admit, my intuition sympathizes with the view you suggest. Indeed, I used to believe that philosophy creates progress myself until only recently -- when I found myself unable to give examples worth taking seriously. (We may insist that Russell's analysis of the definite article established the presupposition of singularity of 'the' -- but, well ...)

Although I do sympathize with your approach, intuitively, it seems to me that there are some problems with such a liberal approach. In particular, I find it difficult to identify 'progress' in a proper way. Would you agree that there can be regress in knowledge? If so, how would you suggest distinguishing cases of regress in knowledge from cases of progress?

Another question is: Would you consider saying (or admitting) that as yet, academic philosophy has not managed to establish any knowledge in the ambitious sense I am applying? -- You may insist that the establishment of knowledge is too excessive as a criterion of the presence of 'progress in philosophy'; and you may even be right. But still: Would you tend to admit that philosophy has never established any knowledge, or would you tend to contradict here?

I'm inclined to agree 'progress' is difficult to identify and my proposal here is perhaps liberal as you suggest. Neither seems troubling to me, however. Some of the issue seems to be that 'progress' is plausibly parsed in various ways based on perspective. What might seem progress internal to a field may seem regress externally; what might seem regress in one sub-field might seem progress in another; what might seem progress for one researcher may seem misguided to another. That said, I see no trouble in treating 'progress' like obscenity, in that we know it when we see it even if we lack a refined definition. I'd add too that 'progress' is a slippery notion, but it's slippery everywhere, not just in academic philosophy. This is not to say of course that some - perhaps many - philosophers don't contribute to progress in any plausible specification. But this isn't peculiar to philosophy. We have sophists; other fields have p-hackers.

I think there is of course regress in knowledge, but regress seems to have distinguishing hallmarks not shared by progress, e.g. loss of knowledge, lack of access to information or practices, which are indexed to practices. I'd count, for instance, the removal of OSF from the web as regress; I'd count defunding of scientific education in public schools as regress too.

To your last question, I think academic philosophy has met your standard insofar as we've made progress on ruling out approaches to answering questions in certain fields and establishing methods for answering questions in others. Few think knowledge can be analyzed as justified, true, belief, due to Gettier's work; compositional semantics exists to a large extent due to Frege; the two most widely used theories of conditionals in linguistics are from Stalnaker and Lewis; Rawls still influences U.S. economic policy for better or worse; Kripke invented the formal machinery underpinning description logics widely used in ontology design; more recently Miranda Fricker's development of epistemic injustice has become influential in clinical intervention strategies for certain groups. Each of these seems progress to me.

"My question is about established 'insights': stable advances, which are largely exempted from any further controvery (about progress ...)." Here I (partially) define the notion of 'progress' applied in the question (I explain what I had in mind when I used the word "progress").

The question aimed at, accordingly, is: "What are the greatest insights [stable advances] academic philosophy achieved during the past 100 years?", ... isn't it?

What I would very much like to know is, Can you answer this question directly? And if not so: Why can't you / can't we answer this question directly?

Perhaps you could provide an example of an established insight in some field outside of academic philosophy to illustrate what you're asking? I feel I've directly answered your question twice now in several distinct ways, so I'm honestly a bit perplexed by your most recent response Friedrich Christoph Doerge

Sorry for this! -- Examples: ... that the earth is not flat, that those areas West of Portugal are not India, that the earth circles the sun, that J.S. Bach died in 1750, that rose bushes need water for growing, that arsen is poisonous for humans, that Walter Scott authored Waverley, that e=mc2.

I'd say the following are established insights or stable advances emerging from academic philosophy within the past 100 years:

(1) Kripke's development of relational semantics, showing the way to formalize modal expressions, clarifying confusion over varieties of modality.

(2) Tarski's truth-theoretic semantics, and distinguishing meta and object languages in formal systems.

(3) Turing's groundbreaking work on computational complexity (often overlooked is that his "Can Machines Think?" from 1950 was published in the philosophy journal Mind)

(4) Insofar as you'd consider aspects of Chomsky's linguistic theory, such as innateness, as established, it's worth noting he defended his theory in several philosophical journals early in his career.

(5) Knowledge is not simply justified, true, belief.

(6) Linguistics, Psychology, etc. are scientific fields with agreed on methods for answering relevant questions in that domain.

This last one is, I think, the most powerful. Once a lot of progress is made quickly in an area of philosophy, it's often the case that progress results in the quick development of a new science. We shouldn't forget provenance.

Thanks, John Beverley, for these suggestions!