One way of getting a handle on what is rational is to look at how things go wrong. What leads us to false conclusions or inappropriate courses of action?
Logical Blunders
The things most often thought of as fallacious are elementary logical blunders. However, these are by no means the most important ways in which rationality breaks down.
Broadest Remit
I intend to pack in under the heading of "fallacies" as broad as possible a range of what seem to me the most important contributors to false beliefs or mistaken actions.
Methodological Factors
I would like to discuss, in the light of a modern understanding of deduction, whether the accepted standards of presentation of arguments in published work have any real value in guarding against fallacious conclusions. In formal logic there are strict preconditions which must be met before any value can be attached to formal derivations (essentially, soundness of the logical system). Are there analogous conditions for informal arguments, and are they being met?
Doctrinal Factors
In classical logic, from a single falsehood all else can be derived. The acceptability of proof by reductio ad absurdum in philosophy suggests that the same consideration applies to informal arguments. There have been many fecund propositions through the history of philosophy which are now considered transparently false, a modern example is the verification principle. What are the modern fallacies and how much of modern philosophy rests upon them?
Institutional Factors
One important factor is the institutional context in which philosophers and other "knowledge workers" operate. While ad hominem arguments are generally ill advised, in this generic context it is reasonable to consider, for example, whether academic institutions provide an environment in which it is in an academic's best interests to speak the truth.


This technique involves covertly adopting a dual standard for the meaning of a concept or claim. The first standard is weak and may be used to establish the claim, the second is strong and may be used for fallacious derivations.
Selfish Gene's
The best example I know of enthusiastic equivocation is to be found in The Selfish Gene notes by Richard Dawkins. Dawkins bases his book around a proposition to the effect that gene's are "selfish" (using a special technical sense of that word) which he proudly proclaims to be tautological. On the basis of this he claims that altruism in individuals is only possible in "special" and "limited" circumstances. Of course, to be effective equivocation must not be too obvious, and to make the claim of equivocation stick is not so easy. But to derive substantive claims about altruism in people from a tautologous premise can't easily be done without equivocation.
A further hint that equivocation is under foot may be found in the comments in the second edition. These are rife with refutation by exclamation mark. Evidently many of Dawkins' readers have believed him to be making claims much stronger than he ever made or intended, which claims he is content to dismiss by dropping his lower jaw.

Of course this does happen, and writing on this topic Dawkins is bound to find his claims exaggerated however sound his arguments may be. Read the book and make your own judgement. Mine is that Dawkins, wittingly or otherwise makes use of equivocation to draw false conclusions from inadequate premises.


Sceptical arguments are nominally intended to refute claims to knowledge. Using powerful sceptical arguments inconsistently can however be used to establish doubtful claims.
The problem with using general skeptical arguments in an argument for some thesis is that you are likely to do more damage than you intend. The trick is to complicate the argument enough to obscure its real power.
in the epilogue of Intellectual Impostures [Sokal97] the authors draw lessons from the texts they criticise. Lesson 6 (p. 179) is that "Specific scepticism should not be confused with radical scepticism", which points out a fallacy similar to that considered here. The idea is that one should not accept a sceptical argument against a specific hypothesis, even though a refutation may not be available, if its implications would be much wider than the specific proposition under consideration.
Quine on indeterminacy of translation
Quine uses a skeptical argument about radical translation to attack the viabililty of the analytic/synthetic distinction. The argument is not a very good argument for reasons which need not concern us here. The important feature to note here is that the argument, to the extent that it is sucessful is so because it demonstrates that the semantics of natural languages are unclear (indeterminate). This used to show that analyticity cannot be established. However, an attack such as this on the clarity of semantics of the language is not confined in its ramifications to analytic propositions. It is equally problematic for synthetic propositions. If the argument were sound it would not only show that we could not establish analytic truth, it would undermine the establishment of any kind of claim whatever.

Bad Theories:

Put forward a bad theory to explain how something works. Then argue from the fact that your bad theory is incapable of explaining a phenomenon to the impossibility of that phenomenon.
Of course, its important that people don't notice that your theory is rubbish. There are two ways to do this:
  1. mention it offhand as a truism, not aknowledging that it is a theory which could be questioned
  2. make it complicated and obscure
Often in this century the bad theory has been about how we learn language.
Wittgenstein on Private Languages
The most celebrated fallacious argument of this kind is Wittgenstein's private language argument.
Quine's indeterminacy of translation
Quine's indeterminacy argument against the tenability of the analytic/synthetic dichotomy is an example if this kind of fallacious reasoning. The details are complex but the principle is the same. No matter how sophisticated or plausible the theory, its failure to explain a phenomenon should count against the theory if the phenomenon is observable, and even if not is inconclusive against the phenomenon. Insofar as I am familiar with them, Quine's arguments against the tenability of the analystic synthetic distinction are based on the failure of putative explanations of how analyticity is to be detected. In the case of natural languages these failures are understandable but not decisive. In the case of artificial languages the explanations are inappropriate.


In the epilogue of Intellectual Impostures [Sokal97] the authors draw lessons from the texts they criticise. Here we list their points and link them to related fallacies documented here.
  1. Its a good idea to know what one is talking about.
  2. Not all that is obscure is necessarily profound.
  3. Science is not a "text".
  4. Don't ape the natural sciences.
  5. Be wary of argument from authority.
  6. Specific scepticism should not be confused with radical scepticism.
  7. Ambiguity as a subterfuge.


Gellner's Words and Things Notes [Gellner59] is sweeping polemic against "linguistic philosophy" and a rich source of information on the sustenance of fallacies.
The Three Fallacies
From an extensive catalogue of doubtful practices Gellner singles out three fallacies as central pillars:
  1. The Argument from Paradigm Cases (APC)
  2. The Generalised Naturalistic Fallacy
  3. The contrast theory of meaning


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