Possible, Plausible, Probable, Proven

I wrote this post for the blog I write for a course, Peoples and Cultures of the World, and originally intended it primarily for a student audience. However, I think it fits well here as well.


“Possible,” “Plausible,” “Probable,” and “Proven” are terms used to indicate rough degrees of statistical probability of something happening or some proposition being true. (My use of the “probable” here reflects the vernacular. When we say that something is probably true, we don’t mean that it has just any level of statistical probability, but specifically that it is quite likely to be true.)

The terms do reflect an ascending order of probability (and a nested one – anything that is plausible is also possible; anything proven is also probable, plausible, and possible), though not in a numerically precise way. They represent a sort of qualitative statistics. When we can realistically indicate precise probabilities, that is obviously a useful thing, but even a rough sense of degree of probability is far more useful than no such sense at all.

Errors in thinking arise whenever we jump up this ascending ladder of probability without evidence, or without sufficient evidence (though admittedly, knowing what counts as sufficient evidence is always tricky business). Just because it’s possible that Bigfoot could be running around the Pacific Northwest or elsewhere doesn’t make it plausible, much less probable or proven.

The Possible

Saying that something is possible simply means that it does not violate the basic laws of logic. In the realm of empirical scholarship, one could also add that it does not violate basic physical laws, that something is both logically and physically possible.

The existence of Bigfoot is possible – it violates no logical or physical rules, but given the overwhelming lack of evidence, there’s no reason to regard Bigfoot’s existence as having anything but the lowest degree of probability. The same goes for claims about extraterrestrial influence in building the Egyptian Pyramids or Stonehenge or the Nazca Lines.

The Plausible

To say that something is plausible is to indicate that it has a higher probability than the merely possible - it is believable, it makes sense. But claims that are merely plausible (that is, that are not also probable) lack the evidence to be taken as having a high degree of probability of truth.

Thor Heyerdahl’s famous voyage on his Kon-Tiki raft from South America to Polynesia certainly proved that it was possible for people to have traveled from the one place to the other using fairly simple watercraft. He even made it plausible that Polynesians could have made voyages to South America, but his voyage alone did nothing to make such notions probable, much less proven. (See this news article from this past summer from Live Science on both Heyerdahl and more recent evidence of Polynesian voyaging to South America that I’ll discuss below.)

An article I encountered this morning on Science Daily, “Early Apes Walked Upright 15 Million Years Earlier Than Previously Thought, Evolutionary Biologist Argues,” makes what I’d consider a plausible claim. “An extraordinary advance in human origins research reveals evidence of the emergence of the upright human body plan over 15 million years earlier than most experts have believed. More dramatically, the study confirms preliminary evidence that many early hominoid apes were most likely upright bipedal walkers sharing the basic body form of modern humans.” So long as there’s evidence, it’s plausible that hominoid bipedalism might be much older than previously thought, but this is an extraordinary claim, and as such requires not simply a single study with good evidence, but a body of good evidence in order to be taken as probable, much less proven by many scholars.

The Probable and the Proven

To say that something is probable means that it is very likely to be the case, that it has a high degree of probability. To refer to something as proven implies that a claim is definitely true, though given the ever present possibilities of faulty observation (even systematic faulty observation), partial understanding or misunderstanding of empirical materials, nothing (at least outside the abstract realm of pure logic and mathematics) is ever demonstrated to be completely and irrevocably true. Instead, to say something is proven is really to say that it has such a high degree of probability of truth that we can pragmatically assume it to be true (though ideally keeping an open mind towards potential counter-evidence).

When Pizarro and his Spanish soldiers reached Peru, they encountered chickens (an Old World domesticated bird) already there. There are at least a couple ways the chickens could have arrived in the New World – they could have been brought by the very earliest European voyages to the Caribbean and Central America in the 1490s and 1500s and very rapidly diffused southward; or they could have been brought by Polynesian voyagers to South America (the only problem there being, at least until now, a lack of evidence of such Polynesian voyages having actually occurred).

When Captain Cook and other explorers encountered a variety of Polynesian islands in the late 18th century, they encountered sweet potatoes, among other crops being grown. As I understand it, there’s no definite evidence of how these South American plants reached Polynesia. They could have been brought by the Spanish to the Philippines early in the Colonial period and diffused from there to Indonesia, Melanesia, and ultimately Polynesia, or they could have been brought back from South America by Polynesians themselves.

New evidence released this past summer addresses this situation. Chicken bones were recovered in Peru that, according to carbon dating, predate Spanish voyages to the Americas by about a century. Further, genetic evidence links the chicken bones to Polynesian varieties of chickens. (See the previously cited article from Live Science and also this article from New Scientist.)

If the carbon dating and DNA evidence hold up (always an important consideration with important new claims), this proves that Polynesian chickens reached Peru at least on one occasion. Given the highly implausible nature of chickens making the voyage on their own (though not logically impossible), it makes highly probable if not proving claims that Polynesians came to South America on at least one occasion. It makes highly probable that the chickens seen by Pizarro were of Polynesian stock as well. I’d even go so far as to say that this new evidence makes probable the idea that Polynesians brought sweet potatoes back from South America directly, though the distinction between plausible and probable is a bit more ambiguous in this case.

Big Men, Chiefs, and Cultural and Historical Comparison

In two posts over the past week (“Not the War of 1812” and “2006 and 1930”) I addressed two recent examples from news and commentary magazines (Time and The Nation) of comparisons between the present moment and events and earlier historical contexts.

Both articles I commented on share a common flaw, a sort of two-step error in identification. First, both authors do identify interesting parallels between certain aspects of the present and particular historical moments, but go beyond this to imply an identity between the contexts, at least in all essential or important regards. Second, they assume that what happened then will happen now and in the near future, or at the least that what happened then is a reliable guide to what’s likely to happen now.

This is an understandable approach. It would perhaps be useful and satisfying to be able to identify historical or cross-cultural situations which highly parallel our current context sufficiently to offer a sort of skeleton key to discern the short term course of events beforehand.

The problem with this is actually fairly simple. Social and historical contexts are unique (i.e. involving a specific set of individuals doing a specific set of things in specific spaces) and simply too complex to discern the sorts of total parallels necessary to accurately prognosticate the future through historical analysis or ethnological comparison.

This doesn’t mean that historical or cross-cultural comparison is not useful or insightful. At best, though, such comparison yields insights into general tendencies and associations – it may yield a useful awareness of likely possibilities if comparison is carefully defined and delimited. Where the comparative approach works best is in lining up commonalities and differences across two or more contexts in an attempt to discern recurring associations between similar aspects of phenomena. In pursuit of this, comparison works best not through any attempt to identify contexts which parallel one another in a total sense, but actually through comparing situations that are both similar and different in important regards (where difference allows for more clear discernment of enduring associations, even in contexts which otherwise differ).

As a side note, useful historical or sociocultural comparison pursues nomothetic generalizations, the identification of associated patterns which tend to co-occur across a variety of settings. As such, it is not opposed to idiographic scholarly approaches which focus on careful description and analysis of particular settings. Instead, careful comparison depends on thorough-going idiographic work having been done on the contexts under comparison. Further, neither idiographic nor comparative nomothetic scholarship are exclusive to any style of scholarly work – either can be conducted using any number of data collection and analysis techniques.

An example of a useful ethnological comparison can start to be discerned in Marshall Sahlins’ classic essay “Poor Man, Rich Man, Big Man, Chief.” In this article, Sahlins presents an important distinction in political organization between the island cultures of Melanesia and of Polynesia (with regard to Melanesia, it seems apparent to me that he’s mainly talking about island Melanesia and coastal New Guinea, but not particularly the interior areas of New Guinea – at least when it comes to identifying key cultural features). While also laying out important social parallels between the two cultural areas, he notes the predominance of “Big Man” political organization (characterized by small polities, and personal influence but not authority of political leaders – the “Big Men”) in Melanesia and of chiefdoms in Polynesia (characterized by larger polities, with chiefs coming into political offices with both power and authority). He doesn’t really make an argument about causation in the article, but he does also note one other suggestive distinction between the two areas, specifically that Melanesian culture tends to be associated with smaller resource bases (smaller islands or interior valleys largely isolated from others by the rugged terrain in the interior of New Guinea). This in turn would mean smaller surpluses that could be extracted and concentrated to form a permanent political elite that can effectively maintain its power and authority through things like full time armed cadres of supporters.

The sort of comparison started by Sahlins in that article can, I think, be usefully extended to make the association between size of resource base and scale of political development clearer if the comparison is fleshed out via more recognition between important cultural differences within Melanesia that still remain associated with the factors identified by Sahlins. In many ways, coastal and island Melanesia is more like Polynesia than like the interior of New Guinea. Linguistically, Austronesian languages are prevalent throughout the coastal and island areas of both Melanesia and Polynesia, in contrast to the prevalence of non-Austronesian languages in interior Melanesia. In terms of subsistence patterns, coastal and island Melanesia and Polynesia emphasize marine resources to provide plentiful protein, alongside cultivation of a variety of tuber and orchard crops and domesticated pigs. Interior Melanesia emphasizes much the same crops and the pigs, but instead of heavy utilization of marine resources, farming is supplemented with gathering and the hunting of terrestrial game animals – arguably providing a somewhat more meager protein base. Interior Melanesian societies are often much more male dominated, with a fratriarchal form of male domination, than is the case with either coastal / island Melanesia or Polynesia. (Whether fratriarchal male domination is related to lower protein resources in tropical forest zones in New Guinea or the Amazon basin was part of what the “Protein Debates” in anthropological scholarship of the 1970s was all about.) Despite major cultural differences between interior and coastal Melanesia, the association between size of resource base and “Big Man” or similar forms of political organizations holds in both portions of Melanesia, and is in fact strengthened by awareness of the important differences.

Cross-cultural or historical comparison is a useful tool in discerning patterns that endure across multiple settings. What we should not realistically expect to encounter are contexts that parallel one another in all essential respects (and even if we did, it would say little or nothing of use about general patterns that operate beyond those two specific settings).