Read these only after you have written your own three sentences. Two of the paragraphs are good, one is not. The question is not which side is right — the lesson does not settle that — but what a paragraph has to do to count as an argument at all.

Model A — the regress reaches the data

I decline to call the letter mere hygiene: it is the Tortoise in a lab coat. Mehra et al. offered premises and a clean inference, and the signatories accepted both — and then asked for something the argument could not produce from inside itself, a commitment that the registry is what it says it is. Grant that and a further demand is available at once: that the audit itself was competent, that the auditors were independent, that the standard of “verified” was the right one. My reason is about the premise step, not the inference rule — the letter never asked anyone to defend modus ponens — but what I claim is that the demand for one more premise and the Tortoise’s demand for one more sentence stand on a single continuum, and that nothing in logic tells you where to stop. The price I pay is that I now owe an account of how science concludes anything at all: my answer is that the stopping point is set by a community’s practice, as the Board of Guardians stopped at Snow’s map, and I have to admit that this makes “verified” a social fact rather than a logical one.

What it does: names the side; keeps premise and inference rule apart even while arguing they lie on one continuum; names the price — and pays it with an answer that could be wrong.

Model B — audit is not regress

I sign, and I sign as an auditor, not as a Tortoise. The signatories asked for a premise to be examined: the registry is a claim about the world, it can be true or false, and it can be checked against Australia’s death count. The Tortoise asks for something categorically different — that the rule by which the argument moves be written in as one more thing it rests on — and that demand cannot be met because meeting it would need the same rule again. The two demands are not on one continuum; one has a stopping point (the data match or they do not) and the other has none in principle. The price I pay is that I must say what keeps that line stable when “verify it” can be pushed one step back: my answer is that a premise-audit ends when a claim has been checked by the means its own field counts as checking, and that a reviewer asked to defend modus ponens in a methods section should reply that a rule is not a finding and cannot appear in one.

What it does: the same three moves, on the other side. Notice that both good paragraphs agree on the facts (the form held; a premise could not be verified) and disagree about whether the demand for verification is the same kind of demand as the Tortoise’s. That is where the case lives.

Model C — a paragraph that does not count

I think the Watson letter was right because the data were obviously fake, as the retraction proved, and so the whole argument in the paper was refuted. Also, two hundred scientists can’t all be wrong, and Surgisphere was a tiny company nobody had heard of, so its argument never had any credibility.

What goes wrong:

“The whole argument was refuted” is used for “a premise could not be verified”. The form of the argument was never in question; the letter said so. This is the collapse the lesson names.
The reason is an outcome (the retraction), not what the letter demanded (the registry, its audit). The retraction is evidence that the premise failed, and the paragraph never says which premise or what checking it would have meant.
“Two hundred scientists can’t all be wrong” and “a tiny company nobody had heard of” are ethos, offered as if they were steps. They may sway a reader; neither makes anything follow.
No price. The paragraph never says whether the demand for the data is a premise-audit or the regress, so it owes nothing on either side — and so it has not answered the question.

The checklist

A paragraph counts as an argument when it:

names a side;
gives a reason that names what was demanded — a premise to be verified or a rule to be justified — and keeps the two apart;
names the price the side pays, in the writer’s own words;
answers, or at least states, the strongest objection from the other side.

Model C fails 2, 3 and 4. Go back to your own paragraph and mark it 1–4.