Prescription: retire the words “prescriptivist” and “descriptivist”

If, like me, you like arguments about English grammar and usage, you frequently come across the distinction between “prescriptivists” and “descriptivists.” Supposedly, prescriptivists are people who think that grammatical rules are absolute and unchanging. Descriptivists, on the other hand, supposedly think that there’s no use in rules that tell people how they should speak and write, and that all that matters is the way people actually do speak and write. As the story goes, descriptivists regard prescriptivists as persnickety schoolmarms, while prescriptivists regard descriptivists as people with no standards who are causing the language to go to hell in a handbasket.

In fact, of course, these terms are mostly mere invective. If you call someone either of these names, you’re almost always trying to tar that person with an absurd set of beliefs that nobody actually holds.

A prescriptivist, in the usual telling, is someone who thinks that all grammatical rules are set in stone forever. (Anyone who actually believed this would presumably have to speak only in Old English, or better yet, proto-Indo-European.) A descriptivist, on the other hand, is supposedly someone who thinks that all ways of writing and speaking are equally valid, and that we therefore shouldn’t teach students to write standard English grammar.

I can’t claim that there is nobody who believes either of these caricatures — I’m old enough to have learned that there’s someone out there who believes pretty much any foolish thing you can think of — but I do claim that practically nobody you’re likely to encounter when wading into a usage debate fits them.

I was reminded of all this when listening to an interview with Bryan Garner, author of Modern American Usage, which is by far the best usage guide I know of. Incidentally, I’m not the only one in my household who likes Garner’s book: my dog Nora also devoured it.


Like many people, I first learned about Garner in David Foster Wallace’s essay “Authority and American Usage,” which originally appeared in Harper’s and was reprinted in his book Consider the Lobster. Wallace’s essay is very long and shaggy, but it’s quite entertaining (if you like that sort of thing) and has some insightful observations. The essay is nominally a review of Garner’s usage guide, but it turns into a meditation on the nature of grammatical rules and their role in society and education.

From his book, Garner strikes me as a clear thinker about lexicographic matters, so I was disappointed to hear him go in for the most simpleminded straw-man caricatures of the hated descriptivists in that interview.

Garner’s scorn is mostly reserved for Steven Pinker. Pinker is pretty much the arch-descriptivist, in the minds of those people for whom that is a term of invective. But that hasn’t stopped him from writing a usage guide, in which he espouses some (but not all) of the standard prescriptivist rules. Pinker’s and Garner’s approaches actually have something in common: both try to give reasons for the various rules they advocate, rather than simply issuing fiats. But because Garner thinks of Pinker as a loosy-goosy descriptivist, he can’t bring himself to engage with Pinker’s actual arguments.

Garner says that Pinker has “flip-flopped,” and that his new book is  “a confused book, because he’s trying to be prescriptivist while at the same time being descriptivist.” As it turns out, what he means by this is that Pinker has declined to nestle himself into the pigeonhole that Garner has designated for him. I’ve read all of Pinker’s general-audience books on language — his first such book, The Language Instinct, may be the best pop-science book I’ve ever read — and I don’t see the new one as contradicting the previous ones. Pinker has never espoused the straw-man position that all ways of writing are equally good, or that there’s no point in trying to teach people write more effectively. Garner thinks that that’s what a descriptivist believes, and so he can’t be bothered to check.

The Language Instinct has a chapter on “language mavens,” which is the place to go for Pinker’s views on prescriptive grammatical rules. (That chapter is essentially reproduced as an essay published in the New Republic.) Garner has evidently read this chapter, as he mockingly summarizes Pinker’s view as “You shouldn’t criticize the way people use language any more than you should criticize how whales emit their moans,” which is a direct reference to an analogy found in this chapter. But he either deliberately or carelessly misleads the reader about its meaning.

Pinker is not saying that there are no rules that can help people improve their writing. Rather, he’s making the simple but important point that scientists are more interested in studying language as a natural system (how do people talk) than in how they should talk.

So there is no contradiction, after all, in saying that every normal person can speak grammatically (in the sense of systematically) and ungrammatically (in the sense of nonprescriptively), just as there is no contradiction in saying that a taxi obeys the laws of  physics but breaks the laws of Massachusetts.

Pinker is a descriptivist because, as a scientist, he’s more interested in the first kind of rules than the second kind. It doesn’t follow from this that he thinks the second kind don’t or shouldn’t exist. A physicist is more interested in studying the laws of physics than the laws of Massachusetts, but you can’t conclude from this that he’s an anarchist.

(Pinker does unleash a great deal of scorn on the language mavens, not for saying that there are guidelines that can help you improve your writing, but for saying specific stupid things, which he documents thoroughly and, in my opinion, convincingly.)

Although Pinker is the only so-called descriptivist Garner mentions by name, he does tar other people by saying, “There was this view, in the mid-20th century, that we should not try to change the dialect into which somebody was born.” He doesn’t indicate who those people were, but my best guess is that this is a reference to the controversy that arose over Webster’s Third in the 1950s. If so, it sounds as if Garner (like Wallace) is buying into a mythologized version of that controversy.

It seems to me that the habit of lumping people into the “prescriptive” and “descriptive” categories is responsible for Garner’s inability to pay attention to what Pinker et al. are actually saying (and for various other silly things he says in this interview). All sane people agree with the prescriptivists that some ways of writing are more effective than others and that it’s worthwhile to try to teach people what those ways are. All sane people agree with the descriptivists that some specific things written by some language “experts” are stupid, and that at least some prescriptive rules are mere shibboleths, signaling membership in an elite group rather than enhancing clarity. All of the interesting questions arise after you acknowledge that common ground, but if you start by dividing people up according to a false dichotomy, you never get to them.

Hence my prescription.


It’s still not rocket science

In the last couple of days, I’ve seen a little flareup of interest on social media in the “reactionless drive” that supposedly generates thrust without expelling any sort of propellant. This was impossible a year ago, and it’s still impossible.

OK, it’s not literally impossible in the mathematical sense, but it’s close enough. Such a device would violate the law of conservation of momentum, which is an incredibly well-tested part of physics. Any reasonable application of reasoning (or as some people insist on calling it, Bayesian reasoning) says, with overwhelmingly high probability, that conservation of momentum is right and this result is wrong.

Extraordinary claims require extraordinary evidence, never believe an experiment until it’s been confirmed by a theory, etc.

The reason for the recent flareup seems to be that another group has replicated the original group’s results. They actually do seem to have done a better job. In particular, they did the experiment in a vacuum. Bizarrely, the original experimenters went to great lengths to describe the vacuum chamber in which they did their experiment, and then noted, in a way that was easy for a reader to miss, that the experiments were done “at ambient pressure.” That’s important, because stray air currents were a plausible source of error that could have explained the tiny thrust they found.

The main thing to note about the new experiment is that they are appropriately circumspect in describing their results. In particular, they make clear that what they’re seeing is almost certainly some sort of undiagnosed effect of ordinary (momentum-conserving) physics, not a revolutionary reactionless drive.

We identified the magnetic interaction of the power feeding lines going to and from the liquid metal contacts as the most important possible side-effect that is not fully characterized yet. Our test campaign can not confirm or refute the claims of the EMDrive …

Just because I like it, let me repeat what my old friend John Baez said about the original claim a year ago. The original researchers speculated that they were seeing some sort of effect due to interactions with the “quantum vacuum virtual plasma.” As John put it,

 “Quantum vacuum virtual plasma” is something you’d say if you failed a course in quantum field theory and then smoked too much weed.

I’ll take Bayes over Popper any day

A provocative article appeared on the arxiv last month:


Inflation, evidence and falsifiability

Giulia Gubitosi, Macarena Lagos, Joao Magueijo, Rupert Allison

(Submitted on 30 Jun 2015)
In this paper we consider the issue of paradigm evaluation by applying Bayes’ theorem along the following nested chain of progressively more complex structures: i) parameter estimation (within a model), ii) model selection and comparison (within a paradigm), iii) paradigm evaluation … Whilst raising no objections to the standard application of the procedure at the two lowest levels, we argue that it should receive an essential modification when evaluating paradigms, in view of the issue of falsifiability. By considering toy models we illustrate how unfalsifiable models and paradigms are always favoured by the Bayes factor … We propose a measure of falsifiability (which we term predictivity), and a prior to be incorporated into the Bayesian framework, suitably penalising unfalsifiability …

(I’ve abbreviated the abstract.)

Ewan Cameron and Peter Coles have good critiques of the article. Cameron notes specific problems with the details, while Coles takes a broader view. Personally, I’m more interested in the sort of issues that Coles raises, although I recommend reading both.

The nub of the paper’s argument is that the method of Bayesian inference does not “suitably penalise” theories that are unfalsifiable. My first reaction, like Coles’s, is not to care much, because the idea that falsifiability is essential to science is largely a fairy tale. As Coles puts it,

In fact, evidence neither confirms nor discounts a theory; it either makes the theory more probable (supports it) or makes it less probable (undermines it). For a theory to be scientific it must be capable having its probability influenced in this way, i.e. amenable to being altered by incoming data “i.e. evidence”. The right criterion for a scientific theory is therefore not falsifiability but testability.

Here’s pretty much the same thing, in my words:

For rhetorical purposes if nothing else, it’s nice to have a clean way of describing what makes a hypothesis scientific, so that we can state succinctly why, say, astrology doesn’t count.  Popperian falsifiability nicely meets that need, which is probably part of the reason scientists like it.  Since I’m asking you to reject it, I should offer up a replacement.  The Bayesian way of looking at things does supply a natural replacement for falsifiability, although I don’t know of a catchy one-word name for it.  To me, what makes a hypothesis scientific is that it is amenable to evidence.  That just means that we can imagine experiments whose results would drive the probability of the hypothesis arbitrarily close to one, and (possibly different) experiments that would drive the probability arbitrarily close to zero.

Sean Carroll is also worth reading on this point.

The problem with the Gubitosi et al. article is not merely that the emphasis on falsifiability is misplaced, but that the authors reason backwards from the conclusion they want to reach, rather than letting logic guide them to a conclusion. Because Bayesian inference doesn’t “suitably” penalize the theories they want to penalize, it “should” be replaced by something that does.

Bayes’s theorem is undisputedly true (that’s what the word “theorem” means), and conclusions derived from it are therefore also true. (That’s what I mean when use the phrase “Bayesian reasoning, or as I like to call it, ‘reasoning’.) To be precise, Bayesian inference is the provably correct way to draw probabilistic conclusions in cases where your data do not provide a conclusion with 100% logical certainty (i.e., pretty much all cases outside of pure mathematics and logic).

When reading this paper, it’s worthwhile keeping track of all of the places where words like “should” appear, and asking yourself what is meant by those statements. Are they moral statements? Aesthetic ones? And in any case, recall Hume’s famous dictum that you can’t reason from “is” to “ought”: those “should” statements are not, and by their nature cannot be, supported by the reasoning that leads up to them.

In particular, Gubitosi et al. are sad that the data don’t sufficiently disfavor the inflationary paradigm, which they regard as unfalsifiable. But their sadness is irrelevant. The Universe may have been born in an inflationary epoch, even if the inflation paradigm does not meet their desired falsifiability criterion. The way you should decide how likely that is is Bayesian inference.