A Mini-Course In Critical Thinking For Writers. Concept 1.7: Distinguishing Best Explanation From Ad Hoc Explanation

I thought I would attempt the first draft of a college-level textbook, writing it directly into my blog, bit by bit. Feedback and recommendations in the thread comments are welcome, either encouraging or critical. The first chapter would be a mini-course in critical thinking for writers. To have a look at Concept 1.6, click here; Concept 1.5, click here; for Concept 1.4, click here; for 1.3 here; 1.2 here; 1.1 here.

Concept 1.7. Distinguishing best explanation from ad hoc explanation. A sign that you may not be seeking the best theory surrounding the truth of a matter, and instead protecting a favored theory—one you want to be true over all others—is if you’re doing a lot of ad hoc reasoning in response to objections to it. We might call this ad hoc-ing. Ad hoc is Latin for for this explanation or moment only or add here for a special purpose, as when a business or bureaucracy forms an ad hoc committee to address an unforeseen situation. Ad hoc reasoning is deployed in, as it were, unanticipated or emergency situations; i.e., situations where a thesis or claim has failed to foresee an important objection or is at an impasse. When you engage in ad hoc explanation, you’re trying to save a favored thesis or belief from pointed and skeptical questions—or new and disconfirming data or competing theses—by seat-of-the-pants rationalizing that cannot be generalized to other theses of the same type. Here are two example sentences deploying ad hoc (seat-of-the-pants) reasoning:

My psychic powers failed today because the audience had too many doubters in it.

UFOs exist, but they never land on the White House lawn because they prefer not to be seen.

These explanations save the theses in question (the claims that psychic powers and UFOs are real), but at the expense of adding additional claims to them (psychic powers are real and they don’t work in the presence of doubters; UFOs are real and they don’t want to be known). That is, they add convenient, “just so” premises to blunt the force of obvious objections: If you have psychic powers, why did they fail in the presence of witnesses today? If UFOs exist, why do they never land on the White House lawn?

With the addition of a premise (a claim supporting another claim) to each thesis, the theses become less simple and probable—though still logically possible. In ad hoc premise adding, skeptical questions and new data are not really being anticipated or naturally incorporated into a theory or claim, but deflected with an additional claim or premise that is logically possible, but maybe not subject to empirical verification (reality testing). The ad hoc explanation, with each new premise added to the original claim, thus renders the explanation less plausible. But because there are lots of logically possible ways that the world can be that cannot be verified by evidence—we may, for example, be a dream in the mind of a butterfly—if you are willing to believe things absent evidence, then you can engage in a lot of “ad hoc-ing” to save your favored beliefs, theories, explanations, and behaviors from skeptical inquiry and new data. Ad hoc premise generating can also be a sign that someone is arguing in bad faith (their motivations for posing such explanations are something other than the truth or the good).

One way to push back against ad hoc rationalizers is to deploy in response Occam’s razor, formulated by William of Occam (1285-1347), in this manner: “No more things should be presumed to exist than are absolutely necessary.” That is, if you can keep things simple, do it. Don’t multiply premises unnecessarily. Ad hoc, seat-of-the-pants rationalizing, multiplies premises. Occam’s razor shaves them off. Maybe psychic powers fail in the presence of skeptics—and UFOs never land on the White House lawn—because neither psychic powers nor UFOs exist.

“Seek simplicity and distrust it.” So the principle here is: quite often–and arguably, most often–the simplest explanation is best. And in some instances, mathematics can be deployed to support Occam’s razor. As a matter of sheer probability, for example, two inductions being true are always going to be at least slightly less likely than a single induction being true. Each time a premise is added to an inductive thesis, the odds of the combined premises being true must necessarily come down (induction, recall, is about probabilities, not certainties). If, for instance, you’re 90% certain a particular woman is a Democratic voter, 90% certain she’s vegetarian, and 90% certain she signed your friend’s animal rights petition, the odds that you are actually right about all three of these in combination is not 90%, but drops statistically to 72% (.9 x .9 x .9 = .72). If you also infer, say, with a confidence of 65%, that she’s a feminist, then the odds that she’s all four of these things come down further still (.72 x .65 = .468 or 46.8%). With just four inferences or assumptions surrounding the woman in question, your odds of being right about her on all of these matters have plummeted to under 50% (assuming you scaled your levels of confidence surrounding each claim accurately in the first place). Occam’s razor proceeds with caution in the multiplication of premises, thus increasing our odds that we’re on the right track.

But a caution to simplicity (Occam’s razor) as a criterion for evaluating truth is offered by the mathematician and philosopher, Alfred North Whitehead: “Seek simplicity and distrust it.” Why distrust it? One reason is that humans tend to find comfort in things they can control, and simple models or explanations might thus serve an emotional bias for control, distorting the complexity of the matter at hand, as in the politician’s behavior can be summed up in one word: greed. If you accept this simple heuristic (rule of thumb, model) for the politician’s behavior, you’ve got a lot of control over the processing of news you encounter about him or her, and you don’t have to expend energy thinking about it, but you may judge their words and actions wrongly, or fail to anticipate how their actions might impact your life. Simplicity as a criterion can arrest a deeper inquiry, and can open people up to such things as the availability heuristic (landing on the nearest and simplest rule of thumb, model, or map that comes to mind for explaining a problem or situation). Occam’s razor, used too casually, can signal lazy thinking.

So ideally, the critical thinker wants to locate heuristic rules of thumb, models, and maps that–like Goldilocks in search of her soup, chair, and bed–are just right. (That is, useful and attending to the right signals in the noise, neither more nor less complicated than necessary.)

Writing 1.7.1. Imagine yourself as a playwright or screenwriter generating a funny scene between two characters. One has made a claim that is a lie, and the other is suspicious. Have the lying character field and answer pointed questions from the skeptical character, engaging in ad hoc, seat of the pants, explanation all the way.

Writing 1.7.2. Select a claim you regard as especially complicated, and unnecessarily larded with unnecessary and ad hoc rationalizations, and write a paragraph slicing and dicing it with Occam’s razor. What’s a simpler explanation or thesis, and what makes it better than the claim you’re deconstructing?


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About Santi Tafarella

I teach writing and literature at Antelope Valley College in California.
This entry was posted in atheism, critical thinking, david hume, education, edward feser, Lucretius, philosophy, reason, rhetoric, science, Uncategorized, writing. Bookmark the permalink.

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