Two decades later, he has yet to recapture the fame he enjoyed when he left that show. To his thinking, though, he has moved steadily closer to his own ideal of what comedy can or should be. Macdonald speaks often about a kind of Platonic form of a joke whose punch line is identical to its setup. He feels he came close in 1995 on “Weekend Update”: “Julia Roberts told reporters this week that her marriage to Lyle Lovett has been over for some time,” he said, as a picture of the country singer’s asymmetrical face appeared behind him. “The key moment, she said, came when she realized that she was Julia Roberts, and that she was married to Lyle Lovett.”

At that time, Macdonald was better known for shocking punch lines than for elegant writing, although the elements of his mature approach were already in place. Over the last two decades, he has grown more devoted to the pure joke, even as comedy has turned away from it. Contemporary stand-up increasingly positions the comedian either as a relatable personality whom audiences can follow from role to role or as a righteous truth-teller. Macdonald is neither. He is resolutely nonpolitical in an industry bent on producing new versions of “The Daily Show,” an ironist working on the same platform as “Nanette.” At a moment when comedians work for applause as much as laughter, by being vulnerable, honest, outspoken, socially relevant, Macdonald is still pursuing the laugh — and nothing more. This anachronistic approach might be limiting his audience, but it could also explain his enduring appeal, because it lends him a kind of moral authority. He is something like a comedy ascetic, demanding a purity that temporal jokes cannot achieve. He seems vital and transgressive again, but pushing 60, he also seems tragic. One thing that makes him a captivating figure onstage is the tension between his refusal to do material about himself and the sympathy you feel for a craftsman who has not been rewarded in proportion to his talent.

At brunch, he cited the ’70s stand-up Robert Klein as saying that when he started, there were 50 stand-ups, and five were funny; suddenly, there were 500 comedians, and five were funny. Macdonald thinks the dynamic Klein described has continued apace, and now the ratio is something like 500,000 to five. He rejected the idea that he was just getting older. “I don’t understand abstract art, but I’m not stupid enough to think it’s worthless,” he said. “I don’t think comedy, though, is that complicated.”

Comedy is a fundamentally social form. You can write a novel at home alone, but it’s virtually impossible to develop a stand-up set without an audience. The structure of stand-up is also rigidly proscribed; while narrative comedy can be about anything, stand-up is almost always about one person addressing the audience directly, without costumes or props. When was the last time you saw a lapel mic instead of a hand-held one, much less a duo or a musical act? The combination of strong audience presence and clearly defined expectations in stand-up encourages comics to try to subvert those expectations. This is anti-comedy: a way to succeed not by making people laugh so much as making them think about the form.

Macdonald is not an anti-comic. He despises anti-comedy, but that has not stopped people from mistaking his work for it, sometimes to his benefit. In 1992, after touring the clubs of his native Canada for the better part of a decade — including a four-month stint opening for Sam Kinison in 1984 — he moved to Los Angeles. There, he heard from another comic that Dennis Miller liked one of his jokes. Macdonald reached out to Miller, who asked him to submit a packet for his new talk show. Macdonald bought a copy of USA Today and went through it article by article, struggling to come up with topical material. He wound up submitting exactly one joke: “Jeffrey Dahmer went on trial today for murdering and cannibalizing 15 men. But I don’t like his chances after hearing what his defense strategy is going to be: They started it.” Miller hired him, thinking his single-joke packet was, as Macdonald puts it, “some Andy Kaufman move.” He wrote for several episodes, then joined the writers’ room of “Roseanne” after the titular Barr saw him doing stand-up. The next year, he got a call from Lorne Michaels.

None of these details appears in Macdonald’s 2016 book, “Based on a True Story: A Memoir” — which, despite its title, is actually a novel. It recasts the events of his life as the exploits of a drug-addled sociopath desperately recycling the same joke about answering machines. (The joke, mentioned repeatedly, is never revealed.) This kind of strategic withholding is a central element of Macdonald’s act. Although he is unmistakably intelligent in real life — Letterman told me he was “maybe the smartest guy in comedy” — he likes to establish a position of ignorance and then lecture his audience from it. Jerry Seinfeld described this approach to me as “sophisticated dumbness” — a technique that makes any glimpse of the real Macdonald feel thrilling. In those rare moments when he chuckles at his own joke or otherwise breaks character, we feel a rush of empathy, as though we have caught the playwright watching from the wings.

This awareness of an amused Macdonald lurking behind the deadpan Norm is what animates his forays into meta-comedy — not the smug refusals of anti-comedy, but genuinely funny subversions that exploit what audiences have come to expect from the form. Consider the moth joke. During a now-infamous appearance on “The Tonight Show With Conan O’Brien” in 2009, Macdonald told a long joke about a moth who goes to a podiatrist’s office. He described in dramatic terms the moth’s complaints — from the boss who delighted in exercising power over him, to the aged stranger he once recognized as his wife, to the son that, he feared, he no longer loved. After nearly three minutes of Tolstoyan elaboration, the podiatrist finally says that he sympathizes, but what the moth really needs is a psychiatrist. “Why on earth did you come here?” he asks. The moth answers, “Because the light was on.” After delivering this punch line, Macdonald stared at O’Brien, only just perceptibly smirking, while the audience cheered.