Humor plays an extraordinary role in everyday life. The traditional Martian observer might marvel at our craving for the incapacitating, nonproductive seizures known as laughter. Many major philosophers have proposed an account of it—an expression of superiority (Plato, Aristotle, Hobbes), the perception of an incongruity (Kant, Schopenhauer), the venting of excess energy (Freud). Each seems to capture some important insight, but not the whole.

Inside Jokes argues that these explanations are typically misdirected. There are no intrinsic properties of jokes or funny situations because humor is a “secondary quality.” A quality is primary if, like the shape or weight of a physical body, it is independent of an observer; it is secondary if, like taste or smell, it is an effect produced in observers, and therefore a product of each observer’s perceptual systems. The mechanisms by which we perceive humor are cognitive. What’s needed is a description of how humor works, of the mental processing involved in finding something funny. A full account will go beyond description to explain not just what humor is but why it exists at all.

The theory here, in rough outline: We cannot function without constantly jumping to conclusions, constructing “mental spaces” through which we interpret the present and anticipate the future. We construct these from current perceptions, free associations, memories, inferences, and so on, and they will inevitably be inconsistent. We are forced to recognize and resolve contradictions that are overt. Thinking Fred is away, I plan to use his office for a meeting, and arrive at work to find him at his desk. But it takes effort to ferret out lurking inconsistencies, whose consequences (if any) may be remote. We have evolved a mechanism that rewards us for detecting them—and that is the basis for “primitive humor.” Art and culture have subsequently exploited this capacity for the sake of conviviality, sexual competition, and stand-up comedy.

Humor happens when I discover that a belief that has entered a mental space “covertly,” and that I have committed to, conflicts with other beliefs in that space. (Proviso: The discovery must not cause strong negative emotions, which may overcome humor’s pleasures.) Consider a scenario proposed by Charlie Chaplin. The camera cuts back and forth between a fat lady taking a walk and a banana peel in her path, zooms in as she approaches it, then shows her stepping blithely over it .  .  . into an open manhole. My attempt at analysis: The setup focuses our attention on the banana peel, brings to the front of our minds expectations about what happens in comedies to someone who steps on a banana peel, and seduces us into the covert assumption that all will be well if he doesn’t. The punch line exposes that mistake. If someone in the next seat says, “He thinks he only needs to walk around it,” that spoils the joke and the theory explains why: The belief that all will be well has been made overt, so contradicting it doesn’t trigger

the humor‑detector.

The reward I get for detecting my own mistake is “first-person” humor. The theory of Inside Jokes holds that I can also get a laugh from “third-person” humor—recognizing an “overcommitted belief” in someone else, who may be fictional. In the scene just described, that hasn’t much kick; the man is a cipher who excites little interest. But make him Inspector Clouseau, defined by the rigor with which he ignores the gap between his beliefs and reality, and the scene could be funny even if a director eliminated the first‑person humor by tipping us off about the manhole. (One consequence of this distinction is that jokes exploiting third‑person humor should be the ones that we can laugh at repeatedly.)

The authors apply their theory to a wide range of examples—jokes, word play, nonverbal humor, found humor, unfunny situations, tickling (a notoriously awkward example), malicious humor, spoiled jokes—including cases difficult for other theories to handle. They evaluate it against a checklist of questions that any good theory of humor should satisfy. For example, why do we laugh only at humans or at anthropomorphized objects? (Answer: We can laugh only at things capable of faulty reasoning, therefore only at things capable of reason.) It is an impressive performance.

But what could it mean to say that a belief has “covertly entered into our mental spaces”? Or that I “commit” to one I do not explicitly entertain? As the subtitle indicates, the theory has implications about our brains, about how they would have to operate in order to provide the proposed humor‑detector. Their picture of mental dynamics is, and is acknowledged to be, wholly metaphorical, an “impressionistic sketch.” The evidence offered in its favor is mostly scholastic, arguments showing why other metaphors proposed in the psychological/philosophical literature won’t do the job.

Their ruling image, with the technical-sounding name “just-in-time spreading activation,” is summarized thus:

Initial semantic contents are activated by sensation in working memory mental spaces, and the process of perception and any deeper thought ensue from the diffusive triggering of related semantic contents and interference patterns therein.

Got that? Its basic meaning is that we build mental spaces as needed, by processes of association. When I step into a new restaurant, the beliefs and expectations summoned up are, by and large, the restaurant basics (the wait to be seated, the size of the tip). New perceptions (the headwaiter’s Gallic accent) elaborate that picture by dragging in associated details (bigger tip? the French for “horse meat”).

It seems fair to say that the authors are confident physicalists, for whom the mind is “just” the brain and who expect neuroscience, eventually, to fill in the details of their scheme, or at any rate make it testable. That raises two questions. First, does the theory suggest interesting experiments, on volunteers observed in the psych lab or brains observed in the imaging lab? Not really—at least, not yet.

More radically, what of physicalism itself, the view that things like neuroanatomy and brain chemistry can give an adequate account of our lived experience, our consciousness? Since, as the philosopher Thomas Nagel famously argued, “We do not have the beginnings of a conception of how it might be true,” the skeptics among us could find the authors’ rhetoric grating—or perhaps fall sullen because, these days, empirical‑sounding talk about “activation,” “diffusive triggering,” and “interference patterns,” or about the inevitable hegemony of neuroscience, is getting all the girls. The authors do enjoy scandalizing skeptics—by speaking, for example, of “stimulus-delivery devices (more traditionally known as the works of art).” And they have a sense of humor, a hip one, partial to Steven Wright, George Carlin, and Steve Martin.

To complete the picture, they want an evolutionary explanation of how our species acquired such brains. A lay reader acquainted with any of the bestselling popular accounts of natural selection and adaptation can anticipate the general line. Consider, for example, third‑person humor, an evolutionary account of which has some ’splainin’ to do. I profit from an ability to detect lurking contradictions in my beliefs, but how do I profit from the ability to detect them in the beliefs of others? One possible explanation is to point out situations in which I could benefit. Suppose that a companion, thinking that a hornet’s nest is just some mud daub on a tree, is about to disturb it. Another is reciprocal altruism. Another is that third-person humor is a “spandrel” that has been “exapted”—an ability that arose as a consequence of selection for some other trait, but proved adaptive and, once in existence, could be selected for.

The authors do not claim to offer more than speculation. To phrase it in a way that might scandalize them, they are engaged in the theological practice of apology, of demonstrating that one’s faith is not contrary to reason. The evolutionary, or quasi-evolutionary, jargon can, however, get out of hand: I defy anyone to show that calling long-lived jokes “memes” that “copy themselves into the future” has more explanatory value than calling it a good story that people like to repeat.

Inside Jokes is clearly and carefully argued. The most fully worked-out part of its theory offers a persuasive descriptive account of the mechanisms of humor, one trailing intimations of an aesthetics—suggesting, for example, that a joke should become funnier if it is reengineered to invoke third-person humor about additional characters, or that good comic timing is what allows an audience “just enough time to make the necessary faulty inference without enough time to double-check it.” (It doesn’t explain the timing required to milk a laugh, though that may concern something different—manipulating not the perception of humor but the social phenomenon of infectious laughter.)

The “reverse‑engineering” of the mind is more the outline of a program than the promulgation of a theory. And it has at least one profound, surely correct, consequence: that anything capable of thinking in a recognizably human way must have a sense of humor.

David Guaspari is a writer in Ithaca.

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