One of the rationality-cluster blogs here on WordPress, Aceso Under Glass, a while ago posted about a concept I find immediately useful: “Butterfly Ideas“. Roughly speaking, hypotheses that need further development, are probably not ripe for serious criticism as they stand, but could benefit from preliminary discussion (read the full post for more).
On this blog and elsewhere, I have repeatedly entertained a variety of “long-distance” linguistic relationships: Nostratic, Uralo-Yukaghir, Uralo-Eskimo, the works, despite not being so far highly committed to any of them. One idiom I’ve previously used to defend this is “big fish are worth angling even if you don’t catch any”; that there are major potential gains for our understanding of history (both intra-linguistic and extra-linguistic) if any of these theories start to prove themselves in more detail. Or as the more succinct modern spin goes, “big if true”. A second motivation is provided by what I have called the “cell theory of language“: spoken natural languages only come from other natural languages, never out of nothing.  This gives a strong prior that all natural languages are, indeed, related, even if we currently lack the knowledge of the details. Factoring in also anthropology further gives strong reasons to believe also in the existence of a number of “bottleneck proto-languages”, such as Proto-Australian, Proto-Amerind or Proto-Exo-African. So big fish are very likely indeed out there, even if we are not sure if our lures are working. Though then these are weaker boundary conditions that do not establish what currently-known families exactly would be the daughters of such a proto-language. E.g. who knows if some American languages might be not Amerind ≈ Beringian, but something else, like para-Na-Dene, pre-Clovis-coastal, Solutrean…? Continuing the metaphor, this would mean we don’t even know how big the fish are exactly, and so also we might not know (yet?) what are the best ways to catch them.
But there’s also a sense in which I think long-distance relationships would be better seen as butterflies than big fish. We do not find relationships in an instant, as sudden flashy discoveries (by “bites” on a “lure”). All spoken languages are in principle compareable, with known typological differences but also universal family resemblance.  The universality of basic phonological categories in particular makes it possible to find some resemblances between any two languages that plausibly could be indicative of some etymological or indeed genealogical relationship. Whether they actually are, depends on additional work on fine-tuning details. Are they above the level of pure chance, and independent of known onomatopoetic and nursery word trends? Are they in conflict with other data of equal value? Do they show recurring sound correspondences, at least some of them nontrivial? These are questions for which we cannot expect to have every answer in place immediately. Any relationship must always begin from observing some similarities that are not probative in itself, and then pursuing this as a hypothesis and seeing if it guides us to more similarities, ones that will not require further costly assumptions to justify.
If all we knew about Finnish and Hungarian were that their verbs for ‘to live’ are, respectively, elää and él, this would not be sufficient evidence to establish them as related languages. But they are, indeed, cognates. Insufficiency or statistical insignificance does not in any way refute cognacy per se. And it is true that checking for more examples of the correspondences e ~ é and l ~ l turns up more evidence such as pelätä ~ fél ‘to fear’. Now with a new correspondence p ~ f, but this does not mean we turn up our nose and declare the hypothesis unworkable: it’s possible to continue and maybe discover, say, pesä ~ fészek ‘nest’. It always takes several steps like this to assemble e.g. a phonological core that will be self-evidently non-accidental. Same for other “evidential cores”, such as partial common morphological paradigms. There is no immediate bite that instantly proves a relationship, but rather, a first weak signal, which will rise in importance once combined with a proper selection of other datapoints.
Any “minimum convincing argument” will not be dozens of steps deep necessarily, but where patience is especially needed is that at any stage there will be plenty of false paths of expansion that will not lead to a workable theory. If at some early point, we had formed a hypothesis of a ~ a, and then run into vapaa ~ szabad ‘free’ (without realizing that both are loanwords from Slavic) — we could still find more evidence also for p ~ b (e.g. by misanalyzing the correspondence Fi. mp ~ Hu. b), but no additional good evidence would be turning up for v ~ sz. At some point we might end up concluding that, yes, this is going nowhere and should be discarded. But then only this comparison! Finnish and Hungarian are still ultimately related, even if their words for ‘free’ are not cognate. Discarding this one comparison does not (should not) mean discarding also any other adjacent comparisons. A burgeoning comparative edifice needs to be open for exploration and individual mistakes, if it is to ever reach any particular rank like “a probable relationship” or “a proven relationship”.
This plea of course has also a corresponding inverse. Anyone who wants a “butterfly” treatment of their ideas has to have enough intellectual humility to recognize that it is, indeed, a tentative first-pass version. All too often I see also people who have a new language relation hypothesis in hand double down on their speculation, and not be open to even constructive criticism. Perhaps in some part there is a misunderstanding where people do not recognize the proposal of better, non-cognate etymologies (borrowing, onomatopoeia, internal derivation) as progress. But certainly also lone-wolf-genius-ism, and its attached incapacity to admit mistakes, is a problem that exists.
On the other hand, I don’t think this side of the problem needs to be focused on too much. In historical linguistics, the exploration of linguistic relationships is already a known research programme, a goal that many people agree to pursue even if we tend to disagree on quite a lot of details. This in mind, if a K. Kookenstein puts out a paper on allegedly showing how English is related to Arabic, but then refuses to consider these comparisons in light of what Indo-European or Semitic linguistics has to say on this: we don’t actually need his approval on this! Language data is not locked, copyrighted, or in any other way tied down to one person, and if desired, it will be possible in any case to check such papers for insights relevant also to better situated IE–Semitic comparison. I know I at least keep a few “Hungarian is too a Turkic language” type works around for this purpose. The intended main thesis is not going to pan out; but any data cited to this end could prove to be regardless still valid. Usually anything of this sort mostly relies on word comparisons (appeals to typology are strangely rare), and these might remain valid as etymologies of any imaginable type… not just Turkic loans in Hungarian, but maybe also old Hu. loans in Tk.; Hu. cognates of Khanty or Samoyedic loans in Tk.; common loans from some third source like Iranian or Yeniseian or Mongolic; some could even end up being evidence for a general Turkic–Uralic relationship. None of this is a priori ruled out, and in this way it may well be possible, with patience, to find meaningful building blocks even within theories that don’t hold up in their entirety. Such is a nifty property of historical linguistics, something that definitely doesn’t generalize to every science.
The two animal metaphors from the start of this post, though, no longer work very well at this point. Some butterflies … may grow up to be big fish, even though most probably don’t? Moreover, I have been mostly illustrating this discussion with disputed-but-definitely-published ideas. More nascent ideas that are simply brought up in a discussion are a different beast for sure. Of course there’s a selection bias here too: the actual butterfly ideas I do have, you will probably not be seeing on this blog as such (and you might have to watch closely to catch any even on my side channels).  Arguably also scientific publishing is “a conversation”… especially any ideas that can be so far found only in some paper draft posted for comments online (in linguistics they’re not even concentrated yet on any arXiv analogue). For these, the original reading of a butterfly idea seems to still work fairly well. This may hopefully help (e.g.) various long-distance proposals to develop better in the end, before they end up with one of two common fates: shelved as not having passed the judgement of Reviewer #2, or self-published with excessive confidence. For this goal, yes, the ball very much is first in the court of people who do have an idea and want to develop it; but it is also in the hands of the rest of us, in being willing to offer first criticism that’s not a complete dismissal. Thirdly, worth noting, all this also depends on a social milieu where people even can find parties interested in discussing some out-there idea.
A further aspect of AUG’s original concept — avoiding unnecessary emotional stress upon people presenting a new idea — I haven’t really even touched here yet. This would be a whole other jar of larvae, but suffice to say I agree that academic discussion, for all its standards of civility, fairly often can have undertones all the way to hostility. This probably scares away many people without a thick skin who might otherwise have had a few interesting things to say; and those of us who do stay engaged, to whatever degree, it may leave with more stress than is necessary.
Some of it, I’m sure, does not even come from a particular need to be prickly, but from limited time… Sufficiently well-known figures in a field tend to get approached by a disproportionate amount of amateurs with A Revolutionary Discovery, unless they specifically keep themselves hard-to-contact, or, perhaps, maintain an aura of not suffering fools gladly. Again a problem that might be softened with other people being open and approachable enough. But this also starts edging towards the general area of science communication and public relations, a bigger fish still to fry that I’m not going to pretend to already have big original ideas for right now (and the butterflies, they will have to wait for other channels).
 The famous case of Nicaraguan Sign Language does not seem to have spoken analogues. In principle there is little directly preventing such a case (and something of the sort, maybe in several gradual episodes, will have to be assumed as the ultimate origin of human language too), but the conditions are unlikely to ever come about. A community of children who are capable of speech but do not have access to any pre-existing spoken language? Sorry, language in general is too adaptive to have been ever abandoned after its first introduction. I will go as far as to suggest that all known human cultures depend strongly enough on language for the transmission of cultural knowledge that any sudden failure of language skills across an entire human group (say, a transmissible disease that induces deafness, fast enough that a signed language does not have time to develop) would not lead to an all-new language being developed a few generations later; it would lead to the group’s extinction.
 In the philosophical sense, not the genealogical one. E.g. despite some exceptions, most languages still have nasal or labial or velar consonants; all but the most impoverished and unbalanced phonological inventories or even just consonant inventories are going to have substantial overlap between them. And even if we did find languages that somehow have completely disjoint phoneme inventories (lazy example: one has only stop consonants and front vowels, the other only continuant consonants and back vowels?), they will not be unbridgably far apart: the known typology of sound change allows hypotheses relating basically any two speech sounds. Grammatical categories, too, can be quite different but still only finitely far apart, where the details of known language histories likewise give us ways to relate non-identical categories to each other (or to derive them de novo language-internally, etc.)
 A freebie for the sake of example though: cf. some very loose thoughts about the subclassification of Oceanic as floated on Tumblr just a few days ago (also already with some, though not highly severe, critique from a regular correspondent over there).