The study of philosophy – whether as an academic discipline, or the individually engaged pursuit of wisdom – has often been called “thinking about thinking.” This is a fairly vacuous description, not because it is wrong, but because it is so egregiously vague as to provide nothing beyond a comfortingly information-free verbalization that does not require us to attend to even a fourth word. 2500 years of written (which is to say, disregarding the purely oral traditions) speculative inquiry merits rather less of a trivialization in my book. Nevertheless, I did think it might be nice to spend a few posts thinking about good thinking from several useful perspectives, focusing, as it were, on the “logic” part of my mantra (Logic, Principles, Evidence, Facts.) This time out the gate, I want to talk a bit about “informal logic,” or that subject which is frequently found under the title of Critical Thinking.

The “critical” in “critical thinking” sometimes throws people off. This is not about being judgmental, or “you’re ugly and your mother dresses you funny” sorts of schoolyard pettiness. No, this is the criticism of the scientist and the art critic, the careful (but merciless!) evaluation of reason, BY reason. No cheap shots, but no free passes, either.

Critical thinking is “informal” logic because the methods are either (1) sufficiently clear for most purposes that there is no need to take the next step of rendering them in formal symbols, or, in some cases, (2) sufficiently complex that they resist formalization while yet yielding to “rules of thumb” that effective enough in most circumstances that one can internalize essential the constellation of relations. Most of the patterns as taught in college classes have the misfortune of merely being defensive in character; which is to say, they indicate how to avoid error, but provide little guidance on how to engage in good (which is to say, rationally justifiable) inquiry. This is unfortunate, since texts on good (which is to say, rationally justifiable) inquiry are really not that hard to find. But such are the vicissitudes of academia.

With regard to the purely defensive aspect, this is the study of fallacies, and (once again) useful compendiums of fallacies are not hard to come by. The Fallacy Files seems to me to be one of the most solid reference sources on the web, while 42 Fallacies is free for the downloading (although it is not as comprehensive as Fallacy Files.)

The number of individually named and identified fallacies is quite large, and while there is value in learning the more prominent ones, the basic issues can be mostly reduced (mostly … ) to a few key principles. Since a fallacy is a claim or conclusion that is somehow illegitimate, we can ask:

1. Was the conclusion derived by valid or appropriate means?
2. Is the conclusion relevant to the argument being made?
3. Is the conclusion true?

Question #1 is exemplified by such errors as the “hasty generalization” – where one jumps to a conclusion from a too small or unrepresentative collection of data. An example of this is found in the climate change deniers who regurgitate the nonsense that, “it is cold where I live, there fore global warming isn’t happening!” There is a reason why it is called GLOBAL warming, rather than “your back yard” warming, and the sad individuals who spout this twaddle only demonstrate their own inability to engage in basic reasoning. Failures of validly derived claims also can occur on more formal grounds. Thus, as a fairly simple example, people who claim there is no right to privacy, because no such right is explicitly mentioned in the Constitution have committed the error of the “enthymeme,” in which their argument is formally incomplete; in order to be formally correct, a missing premise must be supplied. The missing premise in this instance is that, “All rights that exist are mentioned in the Constitution.” Adding this premise makes their argument formally correct, but also shows why their conclusion is demonstrably false. This is because their missing premise is explicitly denied to them by the 9^th Ammendment. (It would be assuming too much to suppose that this is why the claimants leave that premise unstated.)

Another failure of valid conclusion is the “post hoc, ergo propter hoc” fallacy, which is Latin for “after the fact, therefore because of the fact.” This happens when one leaps to the conclusion that because event A preceded event B, A caused B. For example, a child gets vaccinated, the same child then develops signs of autism. Aha! The vaccine “caused” the autism. Now anyone possessed of nothing more exotic than the abstract possibility of reasoning can see through such nonsense without even a second thought. Nevertheless, the anti-vaccine clods spout this sort of drivel with promiscuous abandon, and in complete defiance of every last scrap of real evidence that shows there is no such connection.

(An interesting note about the post hoc fallacy: it might actually turn out to be true – by accident! – that A really did cause B, and yet the claim is still a fallacy! This is because “A caused B” assertion is illegitimately treated as a conclusion to be stated, rather than as a question to be investigated.)

An example of the need for relevance is the argumentum ad hominem, or “argument against the person.” People frequently mistake criticizing another person for committing an ad hominem attack. But in order to be an ad hominem, the claim must either be false or irrelevant. Thus, claiming that, “You can’t believe in global warming: Al Gore says it is happening, and he’s a liberal!” is a blatant ad hominem, since Gore’s political orientation is irrelevant as to the accuracy of his science reporting. (And it isn’t even obviously true that he’s a liberal, as he is really more of a political moderate.) On the other hand, saying something like, “You can’t trust Fred in this matter: he frequently misrepresents facts, and he is not a keen observer,” if it is true and Fred’s testimony is materially relevant to the issue at hand, then no fallacy has been committed. Thus, if someone is an habitual liar, then calling them an habitual liar and rejecting their assertions is not an ad hominem fallacy.

It is important to note that informal fallacies frequently (if not inevitably) come in clusters. Thus, for example, hasty generalization and post hoc fallacies will often be so densely intertwined that there is no effective way of distinguishing the one from the other.

A very good taxonomy of fallacies, both formal and informal, may be found HERE at the Fallacy Files.

One last remark, of both a didactic and a rhetorical nature: there are good reasons for learning to recognize and name a good many of the fallacies discussed by the various resources listed above, and both have to do with the fallacies identified for so long that they have Latin names. The didactic reason is that these fallacies are so common, that they’ve been identified as such since the Middle Ages or earlier. That means they are also the most commonly found fallacies in ordinary human reasoning. Learning to recognize and avoid these errors is a significant step toward good reasoning on your part. The rhetorical part is that if you can correctly identify and accurately provide the the Latin name of another person’s fallacy, it really pisses them off. I mean, what are they going to do, call you a “poopie head”? (An argumentum ad hominem, since your lack of character is irrelevant with regards to their failure of reasoning.)