It continues to be disorienting to Keltham each time his audience of empirical-topologists throws around guesses built out of much more mathematically sophisticated language than you would associate with a dath ilani kid too young to know how 'p -> q' was defined.
"That's about the most plausible wrong guess I can imagine, so congratulations on that. But no. They didn't tell me right away why they knew, that time, the Watchers left it mysterious so I'd have some motivation to learn stuff myself. And I apologize if I'm correspondingly wrecking your own education's most optimal ideal form under ideal circumstances, but we have a planet to industrialize, so I'm going to plow ahead anyways and just tell you, maybe someday your kids will learn it the right way. What my Watchers secretly knew was a completeness or idealness proof, built from more powerful and sophisticated methods I wouldn't be ready to use myself until late in age 12. They defined the most you could possibly reasonably ask for out of a logic, then proved they already had that."
"Consider again our worlds of blue circles, containing red triangles and green squares, and objects related by successorship and multiplication and all the rest. We have said that the subject matter of logic is necessary connections from premises to conclusions. Then the perfect or ideal logic would be one which, given some collection of premises, could derive through its permitted steps of inference every possible conclusion which actually followed from those premises."
"Well, with some fairly high-powered techniques, you can prove that first-order logic does in fact have this property - which means that if you created a new logic which is a single sentence more productive, in the sense that it says even one more thing follows from a premise set, which the logic I showed you cannot derive through its allowed steps, that new logic is making non-truth-preserving leaps; there will be some model, some world, where all the premises are true, but that extra derived conclusion is false."
"The key to that proof, incidentally - I sort of feel like I ought to say this, both to give you some hope that such a proof actually exists, and to make reconstructing all this reasoning easier, if it turns out that the food here is poisonous to me after all and it gets too expensive to keep resurrecting me - is a compactness proof. Oh, nice, you have a word for that, so I'm guessing you used a similar concept in topology? The compactness proof shows that if an infinite set of logical statements has no semantic model - if there is no depictable world or illusion in which all the premises are true - then some finite subset of those statements has no model. We further prove that if a finite collection of statements has no semantic model, we can syntactically prove a contradiction from those statements in a finite number of steps. Then if Q follows from a collection of premises in every possible model of those premises, we can adjoin ~Q as an additional premise to the collection, yielding a collection of premises which has no models; and obtain a contradiction in finitely many syntactic steps; and from this by double negation we can syntactically prove Q in finitely many steps. So whenever Q follows from a collection of premises, we can prove it from those premises syntactically."
"That's the final reason I expected Lrilatha and myself to reason in ways that were not quite so different, even though she wasn't human and possibly hung out with gods. Assuming the whole dath ilani philosophy was true across all planes - though I wasn't quite certain of that, and I'm still not - it wouldn't be surprising if Lrilatha could see some conclusions following from premises faster than I could. But it would be surprising - considering the proof that logic is literally as good as it possibly gets and gives us everything we could possibly want - if Lrilatha could make premise-conclusion leaps of a qualitatively different kind that I could not follow even in principle, using new rules of deduction and permissible derivation that no dath ilani had ever encountered."
"That said, if you introduce the ability to directly quantify over functions or predicates, the proof I described no longer works, but most philosophers of mathematics in dath ilan claim that this can't really be improving the power of the logic, because anything you can actually derive in the syntax of a 'second-order' logic that quantifies over functions, can also be derived inside some corresponding 'first-order' system that doesn't, like this one doesn't. I mention it because I'm now in some totally other plane and ought properly to be less sure of some things than I was yesterday, and if Asmodeus does show up using genuinely valid reasoning I can't follow even in principle, there'd be an obvious immediate guess that he was taking advantage of physical principles that don't exist in my universe but let him directly access the semantics of quantifications over predicates. We were pretty sure that was physically impossible inside our own universe, but this plane might or might not be another story. But, again, I am mostly not expecting that to be the case, and if Lrilatha could do that, she politely didn't do it around me."
"That's the final piece of the concept that 'Lawful' translates into my language - the ability of human beings, even if it's only a little, even if they have to struggle and work hard at it and often it's just faster to run and catch the ball instead of overthinking it - to sometimes know and make a more deliberate use of Laws that are timeless, universal, and even, sometimes, knowably optimal."
"And that's why I heard that Lawful was a god-concept and thought to myself, 'Heh, I bet I know where that's pointing to on at least some things.' There are, in at least some parts of the Law, a single best way you can possibly do it, and then you can't do any better than that. There may be more aspects to god-thought that I can't understand at all, for all that I presently know. But if Validity is a part of the god-concept of Lawfulness at all, then I can take a pretty good guess at which version of Validity the gods are using, which rules they use to decide which arguments follow from which arguments. Namely, any one that's inside the huge equivalence class of possible rules that allow deriving all the consequences of the premises you have, but not deriving any more than that."
"To be clear, I just popped into another dimension, I am guessing at some things rather quickly, I could be very wrong about all of this, and any more Lawful beings around are welcome to show up and tell me so before I mislead the lot of you any further. I do think I have enough dignity not to take offense at being told I made some wrong guesses within my first two days of materializing in another world."
"But it is the obvious thing to suspect, when somebody tells you that 'Lawfulness' is a god-concept. One at once suspects that the gods and smarter Lawful beings will be using forms of the Law that are optimal within certain dimensions - in some cases where I already know which kind of optimality to look for, and that it isn't a very impossible kind of optimality to have, if your brain isn't as completely messy as a human one."