If you’re going to put together an arsenal of paradoxes which may or may not help you against a rogue A.I., there are a few things you should know.

Paradoxes are more than just unexplained phenomena. Some people call it a “paradox” that we have some evidence suggesting certain stars are the same age and other evidence suggesting they’re different ages, but that’s not any kind of seeming logical impossibility… it’s like noticing that one fraternal twin has crow’s feet, probably because he works harder than the other one.

And not all paradoxes are created equal. Some are way too specific, some show shallow thinking, some are restatements of basic ideas found in other paradoxes, and some appear to have been created with the aid of psychotropic drugs (“Dude. Why do we park in the driveway… AND DRIVE IN THE PARKWAY?” “Dude. What’s a ‘parkway?'”). Here, then, are the ones we’ve found most beguiling over the years.

10. Schrodinger’s Cat. The cool cat Schroeder has been put in a closed box by the jealous Lucy. Or something like that. You can’t see or hear the cat. Because of the observer effect, the cat is literally both alive and dead at the same time. Seen in many, many books, TV shows, movies, video games. Dresden Codak‘s treatment is a personal favorite.

9. The Tree in the Forest. If it falls, does it make a sound? How, exactly, do you define “sound?” This, and many paraphrases, figure into lots and lots of arguments, often as a synonym for the observer effect. The idea sometimes translates into fantasy as gods, fairies or entire worlds in danger of fading from existence if their “audiences” no longer hear them. For some fantasy/sci-fi writers, that may be a little too autobiographical to be healthy.

8. Achilles and the Tortoise. The tortoise had a head start in the race. Achilles is catching up. He keeps halving the distance between himself and the tortoise… but will never quite reach it, because adding 1/2, then 1/4, then 1/8 and so on ad infinitum will get you closer and closer to the number 1, but never quite there. The answer to this one will give you a firmer understanding of math in the real world, especially factorials. Seen in: informal calculus, the terrible romcom I.Q.

7. The Barber Paradox and the Set of All Sets. “The male barber shaves every man in town who does not shave himself. Who shaves the barber?” Assuming that every man in town has to get shaven, there is no escape from this dilemma. Bertrand Russell used this exercise to show that certain kinds of classification were impossible. Seen in: the excellent Bertrand Russell comics biopic, Logicomix.

6. The Paradox of the Stone. Can God create one so heavy He can’t lift it? If his power is infinite, what happens when infinity is turned against itself? It’s generally assumed that whether He can or can’t, He doesn’t… except in a few works of fiction and a few mythologies like the Greek, wherein the god/God who created the world finds himself running scared from his own creations like a divine Frankenstein. Seen in: Preacher.

5. The Nihilist’s Challenge. Not its official name, but, fittingly, it doesn’t really have one. Nihilists do not believe anything exists– and defy you to prove otherwise, which is insanely difficult since their thesis challenges any axiom you might use to begin your reasoning. It’s such a challenge that led Rene Descartes to “Cogito ergo sum…” which nihilists didn’t take long to start arguing against. A softer form of nihilism declares the world to be real, but meaningless, or to have no meaning save that which we impose (which is basically Sartre’s Existentialism). Seen in: Rorschach’s origin story and implied in the pitch for Seinfeld, “the show about nothing.”

4. Escher Stairs. We could have picked one of a half-dozen Escher artworks to represent his distinctive, logically challenging artwork, a form of visual paradox. But people always seem most taken with those stairs, perhaps because they’re so immersive. Seen in the movies Harry Potter and the Sorceror’s Stone and Inception, among others.

3. The Problem of Evil. Longtime readers know this is a favorite issue of mine. Time Magazine once put it very succinctly: “God is all-powerful. God is good. Bad things happen.” Some, like Rorschach, simply use the problem of evil as an argument for God’s nonexistence. Others grapple with it all their lives: it is, at the least, a severe challenge to a conventional Christian faith. Addressed very directly in: Penny and Aggie: “What You Can’t Teach.”

2. The Liar Paradox. “This sentence is a lie.” This statement is neither true nor false, merely dickish. The classic A.I.-destroyer, elegant in its simplicity. Seen in: one unforgettable Star Trek sequence.

1. Time Travel. What happens if you go back in time and try to kill your own grandfather? If all time fits together like a jigsaw, as in The Time Traveler’s Wife, then everything is predetermined, including your journey, and you’ll be prevented by some narratively frustrating coincidence. This seems pretty tough to believe, but arguably even harder to swallow is the idea that doing this would spark a wildfire through the fabric of the universe, destroying everything, as claimed in the Back To The Future series. The best-sounding theory (branching parallel universes) still conjures up images of another Earth being created every time a time traveler draws a breath. It may be that our heads are not currently equipped to deal with the true principles of time travel, just as the rules of quantum mechanics mock our intuition. But we’re learning those…

A boatload more paradoxes can be found here and here.

Rather than a list for today, I’ve got a heads-up: I’ve teamed up with Dave Belmore (co-writer) and John Waltrip (artist) to create a brand-new comic for gadget-lovers, updated three times a week (on a slightly less regimented schedule than my other strips). You can find it at http://www.widgetitis.com. Enjoy!

Hey, it’s this thing again! Most of you may not even remember, but Fans used to publish poppy top ten lists like this on a fairly regular basis, usually written by Will Erixon or Tim Mitts. Those guys are busier these days, but I’m giving the “top ten” thing another try for a while, and we’ll see how it works out. Since the comic’s lead characters are currently discussing villains turned to the service of law and order, this seemed like a good place to start.

Please note: these lists are unfair. They are based on my opinions, and my opinions not only vary from yours, they vary from year to year. Comments are welcome, but if my choices upset you then I encourage, nay, bless you to create your own list.

10. Kevin Levin. I don’t know of any kid’s-show characters who’ve taken a path like Kevin’s, from gothy megalomaniac to arms dealer to irritable surrogate older brother. Ben 10 is rarely great television, but it’s a fun way to burn through 30 minutes on the exercycle, and Kevin’s against-the-grain cynicism is the biggest reason why.

Gwen: Oh, you do have a heart!
Kevin: Yeah. That’s what poor people have instead of money.

9. Godzilla. Admittedly, I’m more familiar with the idea of these movies than the actual movies themselves, but who doesn’t love a city-destroying dinosaur who soon has to battle other monsters that would otherwise destroy cities slightly faster?

8. Spike. No, not the author of Templar, Arizona, whom we all know is as evil as ever. Joss Whedon’s Spike was a genuine badass in his early days, but never quite as badass as he wanted you to think, and his posing got more desperate and comical as his heart softened. Despite one or two twists best left forgotten, overall his was the most satisfying of the Buffyverse’s many, many redemption arcs.

7. The “Villains by Necessity.” Eve Forward’s delightful Villains by Necessity thrills, amuses and asks some probing questions about the nature of good and evil through this desperate cadre, most of whom barely qualify as “Diet Coke of Evil,” but who nevertheless have to restore the moral balance of the world before it finally becomes too “good” for its own good.

6. Gru. It takes a certain kind of spirit to dream big, to always fall short, and just keep dreaming, all the same. That’s what makes Despicable Me‘s Gru likable even before the kids start to awaken the joyful child within the man. A lot of what makes him funny for much of the film is his carefree cruelty to kids and to his own childlike minions, but the film replaces this feature, gradually and smoothly for the most part, with an almost equally funny view of him as a put-upon underdog.

5. The Secret Six. Marvel’s Thunderbolts and DC’s Suicide Squad are passably entertaining, but the Squad’s best characters– Amanda Waller, Rick Flagg and Bronze Tiger– don’t really fit the “villain turned hero” mold, and the Thunderbolts’ only mainstays are not terribly interesting. But the Six? They’ve carved out a unique place in superhero comics’ moral landscape, and often seem as likely to die for each other as to kill each other. Catman, in particular, is an inspiration for anyone who’s ever felt like a loser.

4. Severus Snape. Arguably J.K. Rowling’s most distinctive achievement, a man whose life contains bitter lessons that kidlit normally avoids but that children need to learn, sooner than ever these days. Not everyone who doesn’t like you is a bad person, even if they don’t like you for a bad reason. Not everyone who serves the side of right gets any reward for it at all, in the end. Some pain never abates.

3. Clint Barton. Marvel has a boatload of heroes who were once villains, but Magneto, the Scarlet Witch and Quicksilver no longer seem to qualify, Electra’s range is extremely limited, and the Black Widow’s new nanotech angle isn’t doing it for me. But Clint, here’s a guy I’d love to drink beer with, and I hate beer. I don’t care if he’s calling himself Hawkeye or Ronin, he’s a guy who never stops having something to prove.

2. Emma Frost. Has there ever been a homewrecker that could get an audience to cheer for her like Emma Frost? Maybe Angelina Jolie. As is generally true with Marvel Comics, the character’s quality can vary wildly with the writer, but several have given her a complex persona, an investment that’s still paying dividends.

1. The Grinch. He may be a hero for like four minutes of screen time in the animated special (or four two-page spreads in the book), but every time I experience his superhuman (supergrinchian?) surge of power, I get a bit misty. (As for Jim Carrey’s version, er, I’m sure he had the best of intentions.) It’s not about making things right with the villagers, you understand. They’ve already accepted a giftless Christmas. It’s about atonement.

Honorable mentions: Max Damage of Irredeemable, the reprogrammed T-800, Stitch. Darth Vader could have been included on the same basis as the Grinch, but I feel like the last few moments of his life are really Luke’s victory rather than his, and he dies redeemed, but not a hero. If you want to gorge yourself on similar material, TV Tropes has you covered.