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Socrates is still mortal, but fallacies aren’t fallacious

Updated repost of The Fallacy Fork and the Limits of Logic, at 3 Quarks Daily

No quiet moment; Theresa May calls snap UK election (BBC)

I had been waiting for a quiet moment to write about this, but there isn’t going to be a quiet moment, so now will have to do. [Update: these words went up on 3 Quarks Daily last Monday. On the Tuesday, Theresa May called a snap UK General election]

Debaters regularly accuse their opponents of using fallacies. These can be formal fallacies, such as simple errors of logic, or informal fallacies, such as appeal to authority, ad hominem and strawman arguments, among others. If a piece of reasoning depends on any of these fallacies, so it is claimed, the conclusion does not really follow from the premises, and while it might still be true we have not been given any good reason to believe it.1 And so books that discuss logic, and science-promoting blogs (including one I follow), regularly include descriptions of informal fallacies, with stern instructions to avoid committing them.

Sagan warns us against fallacies. But is exposing fallacies enough to shield us from the demons?

In an article entitled The Fake, the Flimsy, and the Fallacious: Demarcating Arguments in Real Life, Maarten Boudry, Fabio Paglieri and Massimo Pigliucci (henceforth BPP) challenge this view. BPP is written for the perusal of trained philosophers, which I am not, but I use it here as a jumping off point, while mixing in further content of my own. (For a discussion by one of the original authors, see here.)

BPP apply what they call the fallacy fork test to accusations of informal fallacy; either the reasoning is obviously erroneous, in which case no one would really use it, or else it is not obviously erroneous in context, and we still have all the work to do. In the first case, formal analysis is redundant; in the second, the facts of the matter need further consideration. Read the rest of this entry

Nonsense from Nagel, and the myth of “common sense”

The appearance of Nagel’s assault on evolutionary science, Mind and Cosmos: Why the Materialist Neo-Darwinian Conception of Nature Is Almost Certainly False, from a position of self-confessed ignorance regarding the underlying science, prompts me to post what I wrote about his methods a few years ago (note BTW the giveaway description of 21st Century science by a mid-19th Century label):

Common sense or utter nonsense?

“Sophisticated members of the contemporary culture have been so thoroughly indoctrinated that they easily lose sight of the fact that evolutionary reductionism defies common sense. A theory that defies common sense can be true, but doubts about its truth should be suppressed only in the face of exceptionally strong evidence.” (Thomas Nagel, Philosophy & Public Affairs 36, 187-205, 2008; posted on FaceBook by Glasgow’s very own Centre for Intelligent Design)

It is difficult to see how one could cram a larger number of logical errors into so small a space.

We begin with an extraordinary smear on the writer’s opponents. The well-informed are labelled “sophisticated”, while to be convinced by the evidence is to be “indoctrinated”. And so, by a populist inversion, the near unanimity of informed opinion in support of evolution becomes an ad hominem argument against it. The suggestion that doubts are “suppressed” is another gratuitous smear, based on pretended ignorance of the robust reevaluation to which all scientific theories are continually exposed.

Reductionism is not defined in Nagel’s paper (in fact, the passage quoted is the only place where the concept is used), so I don’t know how he is using this notoriously slippery word, nor why purported explanations in terms of intelligent design (the proffered alternative) escape this fate, if indeed they do. However, it is worth pointing out that evolutionary explanations by their very nature describe the behaviour of systems, or even (if we restrict ourselves to the last billion years or so) of interlocking populations of systems, the very opposite of reductionism. I find it shocking that a philosopher of mind, of all people, should be unaware of this.

Worst of all is the appeal to common sense. Common sense is an amalgam of received and unquestioned wisdom, unexamined and often unconscious philosophical assumptions, and extrapolations from everyday experience. What appears to be in accord with common sense must depend on how much one already knows. Thus separate creation of kinds may appear to be in accord with common sense to someone who is completely ignorant of the richness of the fossil record, its relationship to the classification of modern organisms from Linnaeus onwards, the reappearance of the same Linnaean patterns in family trees based on molecular phylogeny, and the overwhelming evidence of the antiquity of the Earth. To someone familiar with these things, it will be the concept of separate creation that violates common sense.

Nagel does not tell us what he would regard as “exceptionally strong evidence”, just as he does not tell us what counts as “evolutionary reductionism”, but the evidence for evolution is presumably strong enough to persuade him to renew his annual flu jab. Since he is writing in a journal concerned with public affairs, it is also worth pointing out that it is strong enough to have led to changes in public policy on the use of antibiotics and pesticides, so as to avoid encouraging the (reductionist?) evolution of resistant strains.

However, the appeal to common sense is an intrinsically weak argument for other, much deeper, reasons. Common sense is an appeal to common experience. Much like the “intuition” discussed in Bertrand Russell’s essay, Mysticism and Logic, it is within the domain of common experience that it has the greatest credibility. Common sense tells us that we are standing still on solid ground, that animals and vegetables are different kinds, that space is Euclidean, that the heavens are unchanging, that an object will eventually come to rest if no force is acting on it, and that tables are solid. That the earth is moving, and that the continents themselves are moving across its surface, that a man shares half his genetic information with a mushroom, that matter distorts the space around it, that the universe is expanding, that a moving object will continue along its trajectory until something stops it, that matter is made up out of atoms and that almost all the mass of these atoms is crammed into a tiny nucleus less than one billionth of the total volume, all of these are violations of common sense. Nonetheless, they are fundamental facts of which any educated person should be aware, even at the cost of being described by Professor Nagel as “sophisticated” or, worse yet, “thoroughly indoctrinated”.

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