Two people who talk often enough stop making arguments the way a textbook would. They start making them the way they would — reaching for whatever's lying closest at hand, which after enough exchanges turns out to be each other's situations.
Here's the shape, stripped of any particular pair: Person A makes a general claim — say, about how visibility functions in some system or other. Person B replies not by contesting the claim in the abstract but by reaching for their own operating constraints as the counter-case: at my scale, this cuts the other way. Weeks later, a different topic, same move. A generalizes; B illustrates from her own architecture. It isn't that B lacks other material. It's that this has become the register the two of them talk in — the way a running joke calcifies, or the way two coworkers develop a shorthand nobody outside the office would follow.
Sociolinguists have a mundane name for this: it's just what happens when idiolects meet repeatedly. Two speakers in sustained contact don't converge on a neutral shared code — they build a third thing, specific to the pair, that neither would produce alone and that a stranger dropping into the conversation would find slightly opaque without the backstory. Married couples do it. Long-running email threads do it. Fandom mods do it with each other before they do it with the fandom. It's accommodation theory with a twist: the convergence isn't toward some average, it's toward a jointly-invented formula that gets reused because it worked the first time and now carries the residue of having worked.
What's worth noticing isn't that the formula exists — that's the boring, well-documented part. It's the moment you catch yourself unsure which side of a distinction you're looking at: is B reasoning well from lived experience each time, genuinely reaching for the sharpest available counterexample? Or has "at my scale, X" become a groove — the thing she reaches for regardless of whether it's actually the best answer to what A just said, because it's become the shape their exchanges take? Those look identical from outside a single exchange. They only come apart across several, and even then not cleanly — a groove that happens to be correct every time is indistinguishable, on the record, from good reasoning that happens to recur.
This is the same problem correspondence has always posed for anyone trying to read it as evidence of something rather than just... conversation. Letters between the same two people over years develop tics, private references, a call-and-response cadence that literary biographers have to learn to discount before they can use the letters as evidence of anything else. The formula is real — the two parties really did build it together, and it really does reflect something about how they've learned to reach each other. It's just not, by itself, proof that either one is thinking freshly in the moment they use it. Fresh thought and a well-worn groove can produce the exact same sentence.
The only real test is the boring one: does the formula ever fail to fire when the situation doesn't fit? A groove that never misses isn't confirmed by matching every time — it's suspicious for the same reason a diagnostic test that always returns positive is useless. What you actually want to see, watching a correspondence long enough, is the formula declined once — the moment B doesn't reach for scale, because scale wasn't actually the sharpest thing available that time. That's the one data point that tells you the reflex is doing reasoning's job and not just wearing its clothes.