Here's a quick, reductive, possibly unfair (but probably not) overview of the big broadcast late-night shows circa 2015: They are a parade of stars selling their movies, TV shows and albums to compliant hosts and uncomplaining audiences. The stars' efforts (or words) often are squeezed into bite-size vignettes -- with the word "viral" stamped upon them -- which are then released over the Internet, where most people get their late-night TV fix now anyway.

Did I mention the word "sell" yet? Because late-night TV is very good at selling.

Sure, the hosts are talented, smart, clever, funny and often a pleasure to watch. Their shows are a marvel of modern television magic. Audiences seem happy, and apparently the stars are, too.

But something, of course, is missing.

Let's call that -- for want of a better word -- brains. What's also missing is genuine curiosity, or at least some sense that a big, roiling, complicated world lies just outside the rarefied confines of the air-conditioned studios. A historic election looms, and the country is in turmoil -- but at least Justin Bieber will be on "Tonight" all week.

It's that promise of something smarter, maybe even something better, that arrives Tuesday when "Late Show With Stephen Colbert" premieres (11:35 p.m., CBS/2). The clues are in its guests.

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Over the next two weeks, Stephen Colbert will have a sitting vice president (Joe Biden), two presidential candidates (Jeb Bush, Sen. Bernie Sanders), a Supreme Court justice (Stephen Breyer) and the U.N. secretary general (Ban Ki-moon). He'll have on a few actresses to whom the adjective "brainy" is sometimes appended -- like Lupita Nyong'o of "Star Wars: The Force Awakens" and Emily Blunt, as well as a couple of actors (George Clooney, Jake Gyllenhaal) who are similarly accorded.

Just to be clear, David Letterman's legatee is not about to turn "Late Show" into "Charlie Rose." This is late-night TV, not public affairs TV. There will be comedy, and skits, and plenty of stars on the promotional circuit. Nevertheless, first steps are significant, and these seem symbolic, too.

During the recent TV critics' press tour, Colbert said a key reason he wanted to drop his old character from "The Colbert Report" is that "I had done everything I could with him or everything I could do with that show, other than have my honest interest in my guest, which is almost constant.

"That was the most energetic, the most exciting part of the show to me. And now I don't have to hold back at all. . . . Now I can just talk."

What's also missing in late-night broadcast TV right now is a true sense of the moment -- that the world is changing, for the better or worse -- and what's required is a comic voice to make some sense of that change -- or, at the very least, to savagely ridicule it. Colbert has already proven he can do both.

There's an enduring myth that Johnny Carson once treated "Tonight" as sort of a late-night salon, where writers (Norman Mailer), senators and stars dropped by. While almost true in the late '60s and early '70s, by the end of Carson's run, "Tonight" essentially turned into the template that remains to this day.

But Carson always understood one true secret -- also the true power and glory -- of this gig: that his audiences sometimes wanted to laugh and think, and he alone could help them do both.

"The goal is to have fun with my friends," Colbert said on "CBS Sunday Morning" the other day. "That means sometimes talking about things that you care about. We're going to want to be talking about what's going on in the world."

Johnny just might approve.