@Causative.. OK, fair enough. Answer this Q, then use your answer to answer my previous query.

No, there is no single consensus. There are several theories of truth. plato.stanford.edu/entries/truth If you ask me, truth is the propositional attitude that a reasonable person would eventually settle on after investigating all the direct empirical evidence and thinking it through. This is a hypothetical state, because no actual person is totally reasonable, nor is any actual person able to investigate all the direct evidence, nor is any actual person able to think any moderately complex issue through from truly all angles.

@Causative are we now talking Pierce

Yes, approximately. I prefer to talk about a "reasonable person" rather than a "community of inquirers." Nothing is gained by multiplying the number of people involved; the hypothetical quality desired is reasonableness. Also I reject Peirce's notions about what statements can and can't be true - I am more inclusive, allowing that a reasonable person could eventually settle on a propositional attitude about metaphysical claims.

@Causative Gotcha. So under these conditions/constraints is there a distinction to be made between "rhetoric" and sophistry'?

Is there an answerable question, or is this a discussion prompt? What it currently asks is either trivial or should be read in encyclopedias.

@Conifold the arguably answerable question, which I deleted in response to Causative's comment was: How should the difference between rhetoric -- the art of effective or persuasive speaking or writing [to, at its best, according to Plato/Aristotle, in good faith/ingenuously persuade another of the "truth" of a "true" proposition],

and sophistry-- [according to Plato/Aristotle] the bad faith/disingenuous use of rhetoric to persuade another of the "truth" of a proposition known to be untrue [or whose truth value is unknown], be characterized when the criteria for "truth" (for whether a proposition is true or false) is "consensus" (agreement within a conversational community of "experts" in a domain), rather than [isomorphic word-world] "correspondence"?

Sophistry is basically dishonest, where the speaker deliberately appeals to fallacious or unreliable justifications that the speaker would not wish to adopt for himself, but is trying to fool the listener into adopting. In honest discussion, the speaker tries to persuade the listener according to justifications that the speaker himself considers reasonable and approves of. An honest speaker may still commit fallacies by accident, but at least it is not done with intent to mislead.

The original question was far more suitable, I edited it back in. Speaking of Peirce, his criterion was only operable "at the end of inquiry", after countless generations passing the torch, and hence, ironically, impractical. How good faith rhetoric should be distinguished from sophistry in practice is quite a different question, with both epistemological and ethical overtones. In particular, a speaker may well be acting in good faith even if they go against the consensus, either knowingly or unknowingly. But in the former case, full disclosure would be in order.

@Coinifold I agree. What is most salient is that "countless generations pass the torch", or, to use a term currently [often for good reason] in disrepute, "tradition." And, clearly, as a criterion, a temporal "end of inquiry" is inaccessible. And thank you for both your edit and youe response. As an aside, I posed the question after rereading (decades later, at the behest of a young relative), the last few chapters of Robert Persig's Zen and the art of motorcycle maintenance. Whose take on how the greek sophists have been given a bad rep remains an enigma to me. Hence the query.

But truth is presupposed by both concepts

Havin said that, science works that way: the current articulated opinion of experts is the citeria.

@causative, so according to your definition of truth, a proposition can be true but wrong? Because here are lots of questions where a reasonable person looking at all the evidence can reasonably come to the wrong conclusion. If you are going to use "true" for such a proposition, what word do you use for a proposition that an unlimited intellect with unlimited information and unlimited integrity would call "true"?

@DavidGudeman When I say all the evidence I don't just mean all the evidence we have practically available. I mean every observable fact from any perspective. A reasonable person looking at all the evidence and thinking it through from every angle is effectively the same as an unlimited intellect with unlimited information. In the limit of investigation, the reasonable person won't be wrong. (What could prove him wrong? Only additional evidence, but the premise is he already saw and considered it all.)

@Conifold, first a quibble: a reasonable person with all the evidence is not the same as an unlimited intellect because a reasonable person has limits to how much he can do and is also prone to mistakes. More substantively, taken as any sort of definition of truth, this proposal leads to an infinite regress on how anyone knows the evidence is true.

@Conifold, actually, I should have said it leads to an infinite regress on what it means for the evidence to be true.

fwiw, i was going over some old reading about this, the other day. rorty seems to claim that truth does not "mean" reasonable belief but that it is "indistinguishable" from it. so i think you just need find cases when it is meaningfully different (brainwashing e.g.) rather than has utility.

@DavidGudeman The set of all possible evidence is taken as a base truth that is a property of the universe. It's taken as given. It is limited to direct observations and does not involve any theories or explanations. The reasonable investigator expands this set of base truths to include theories/explanations. That is why it's not an infinite regress; it explains one class of truth (theories) in terms of a different class of truth (observations). (Also, yes, a reasonable person is prone to mistakes, but given enough time they can notice and correct their mistakes.)

@Conifold, that doesn't work as a definition of truth for two reasons: first, the base truths are left undefined--what does it mean for them to be true? Second, whatever you say in response to that, we are left with two definitions of two properties: base truth and inferred truth. What reason do we have to think that the two properties are even related, much less a single property? And you still have the third problem of explaining what your reasonable investigator is trying to accomplish by taking one propositional attitude rather than another. What is he aiming at if not truth?

@DavidGudeman Consensus is not meant as a definition of truth, one would not be able to go against it in the name of truth otherwise. But since we cannot intuit the reality raw, peek into the mind of God or time travel to the end of inquiry some surrogate is needed for here and now. It is as good as any.

If truth were some consensus not unlike some scientific community, then good faith rhetoric would just simply need to check the validity/objectivity of the said consensus position with its poll and persuade others such an objective result. Essentially becomes an honest professional journalist. Sophists would simply need to persuade people for a false or fictional consensus if such is a goal for them...