Some knowledge is not certain (or why the spurious rejection of reasonable inductive inferences is itself a fallacy of reasoning)

One of the common themes of the creation wars and the climate war is the attempt by the anti-science side of each debate (ie, creationists and AGW deniers) to make their position appear more reasonable than it is by arguing that it is accepted by a large number of scientists.  Thus we have lists of scientists who do not accept evolution such as that compiled by the Discovery Institute, and equivalent lists of scientists who do not accept Anthropogenic Global Warming such as the OISM petition from the forces of anti-science.

To counter this spurious argument, defenders of science have emphasized how small a proportion of scientists accept these pseudo-scientific positions.  The NCSE does this with some humour, through their Project Steve.  Defenders of the theory of AGW are a bit more dour, and have produced a series of surveys and other studies showing that rejection of AGW is confined to about 3% of climate scientists.

The curious thing is that these studies are rejected in turn by AGW deniers as an appeal to authority, ie, and invalid argument.  Their intention is nothing of the sort.  Rather, they are a rebuttal of the spurious appeal to authority represented by such phenomenon as the OISM petition.  Ignoring that important subtlety, however, the fact remains that an appeal to relevant authority is in fact a valid way of justifying beliefs.  I recently explained why in some detail in a comment at Skeptical Science, which is reproduced with minor editing below the fold.




dhf @40:

"Very many are trained through education and profession to recognize and disregard arguments containing logical fallacies."

Being in fact trained in formal logic, and having some practical experience in rhetoric, I can recognize your argument as an "argument from assertion".

Of course, that does not make it a logical fallacy.  A logical fallacy is formally described as an "invalid argument", ie, and argument for which the premises can be true, and the conclusion false.  Clearly, the argument by assertion, as the formal form of p⇒p (read as p, therefore p, where p is any proposition).  That is so far from being a logical fallacy, it is in fact a tautology.  It also in no way gives us more reason to believe that "p" than we had initially, and is thus a rhetorical fallacy (or from some points of view, a strong rhetorical move if you can disguise what you are doing.

Unfortunately, that which you argue for by assertion is false.
I know that because both induction and abduction are also logical fallacies.  (I leave aside mathematical induction, which may be formally valid, but cannot be shown to be formally valid without assuming that it is.)

In the classic example of induction is the argument that because all (non-albino) crows that we have seen are black, therefore all (non-albino) crows are black.  Clearly the proposition that all members of a set, S, have a given property is not logically entailed from the fact that all members of a proper subset of S, S', have that property.  But the argument from induction asserts that inference to be valid.
Ergo the argument from induction is a logical fallacy.

To take a practical example, it is a universal experience of humans that not all points of the Earth's surface are directly visible from one location no matter how high.  It does not follow logically from that that tomorrow no human will directly see the entirety of the Earth's surface from one location. Assuming that they will is a logical fallacy, known as the argument from induction.

An even more practical example is the belief that that aspirin has a high probability of reducing the pain from a headache (supported by a vast body of experience) will continue through tomorrow.  It is logically consistent with all past experience that from tomorrow aspirin will cause humans to die after 48 hours of excruciating agony.  Any time you take aspirin in the confident belief that it will reduce your headache and cause no appreciable harm, you are indulging in the logical fallacy known as induction.

Abduction (the inference to the best explanation), is even more fun in that it has the apparent form of a named fallacy, ie, that of affirming the antecedent.  It is none-the-less the basis of all science.  Admittedly, some scientists try for a Popperian science, but as even Popper admitted, falsification is a matter of convention - and hence even Popperian science is inductive.  Indeed, as Imre Lakatos has pointed out, the inductive leap based on the fact that a theory has not been falsified is always false.  As he says,

 "In the distorting mirror of naive falsificationism, new theories which replace old refuted ones, are themselves born unrefuted. Therefore they do not believe that there is a relevant difference between anomalies and crucial counterevidence. For them, anomaly is a dishonest euphemism for counterevidence. But in actual history new theories are born refuted: they inherit many anomalies of the old theory. Moreover, frequently it is only the new theory which dramatically predicts that fact which will function as crucial counterevidence against its predecessor, while the "old" anomalies may well stay on as "new" anomalies"

It is clear from that last example that the very professions you probably had in mind (medical doctors, engineers) are not trained to ignore arguments based on logical fallacies.  Rather, they base their careers on at least one logical fallacy, and probably many.  Indeed, certainly many if they are any good.

Appeal against an argument because it is a "logical fallacy" really amounts to the old classical canard of assuming all knowledge is certain - that only that which can be known deductively can in fact be known.  In fact, in real life most of what we know is known inductively - from arguments that are not formally valid, but are reliable.  That is necessarily the case, or our knowledge would be restricted to logical tautologies, and mathematics.  Indeed, at a most fundamental level, did we not accept the argumentum ad populum in our youths, we would speak no language.  It is only because all around us (or nearly all) call crows "crows" and swans "swans" that we know the meaning of those words.

The reason some (at least) of the "logical fallacies" have such a hold on our minds is that they are in fact reliable ways to obtain knowledge, or at least were so under the conditions in which we evolved.  Under those conditions the knowledge base of all the people was based on their every day experience of the world over generations, and within its limits was reliable (although it could sometimes be false).  We did not need to check that black mambas were poisonous because we were told so by "all the people", and trusting them was a far more reliable way to obtain that knowledge (even if less certain than direct experimentation).

Not only were they reliable, they were essential.  No person growing up has time or ability to check every fact they accept for themselves.  That was true in the past and is even more so in modern societies with a substantial scientific and technical base.

What has changed with the development of science is not that we need no longer rely on "arguments from authority" or "arguments from all the people", but that we have realized the reliability of the people on whom we rely depends essentially on the type of experience they have.  We have realized with respect to science that reading ancient Greek classics is not a reliable source of knowledge, but that detailed experimentation and scientific reasoning is.  Therefore we no longer include classics scholars among the people we rely on to understand physics.  Instead we rely on scientists.

Doing so, of course, remains a 'logical fallacy'.  It is also a reliable guide to knowledge.  The key is we must ensure that scientists do not themselves rely on the argumentum ad populum in the area of their specialization.  Rather, they should rely on those other 'logical fallacies', induction and abduction.  So, unless you are yourself a climate scientists, you are a fool to not rely on the 97% in determining your knowledge on science.  You are giving up the most reliable source of knowledge to which you have access.  You are even more a fool if you do so based on myths about "logical fallacies" which have no bearing on the real world.

Climate scientists themselves, on the other hand, should not be persuaded one iota in any direction from the fact that they are in the 97%, or the 2% or the 1%.  And from my experience of their works, they are not.