As the world marked the 50th anniversary of the JFK assassination, I have to confess … no, no, not that I was in on the plot. I wasn’t even born then, silly. I have to confess that, in between struggling to make a paper deadline, attending a workshop in Princeton, celebrating Thanksgivukkah, teaching Lily how to pat her head and clap her hands, and not blogging, I also started dipping, for the first time in my life, into a tiny fraction of the vast literature about the JFK assassination. The trigger (so to speak) for me was this article by David Talbot, the founder of Salon.com. I figured, if the founder of Salon is a JFK conspiracy buff—if, for crying out loud, my skeptical heroes Bertrand Russell and Carl Sagan were both JFK conspiracy buffs—then maybe it’s at least worth familiarizing myself with the basic facts and arguments.

So, what happened when I did? Were the scales peeled from my eyes?

In a sense, yes, they were. Given how much has been written about this subject, and how many intelligent people take seriously the possibility of a conspiracy, I was shocked by how compelling I found the evidence to be that there were exactly three shots, all fired by Lee Harvey Oswald with a Carcano rifle from the sixth floor of the Texas School Book Depository, just as the Warren Commission said in 1964. And as for Oswald’s motives, I think I understand them as well and as poorly as I understand the motives of the people who send me ramblings every week about P vs. NP and the secrets of the universe.

Before I started reading, if someone forced me to guess, maybe I would’ve assigned a ~10% probability to some sort of conspiracy. Now, though, I’d place the JFK conspiracy hypothesis firmly in Moon-landings-were-faked, Twin-Towers-collapsed-from-the-inside territory. Or to put it differently, “Oswald as lone, crazed assassin” has been added to my large class of “sanity-complete” propositions: propositions defined by the property that if I doubt any one of them, then there’s scarcely any part of the historical record that I shouldn’t doubt. (And while one can’t exclude the possibility that Oswald confided in someone else before the act—his wife or a friend, for example—and that other person kept it a secret for 50 years, what’s known about Oswald strongly suggests that he didn’t.)

So, what convinced me? In this post, I’ll give twenty reasons for believing that Oswald acted alone. Notably, my reasons will have less to do with the minutiae of bullet angles and autopsy reports, than with general principles for deciding what’s true and what isn’t. Of course, part of the reason for this focus is that the minutiae are debated in unbelievable detail elsewhere, and I have nothing further to contribute to those debates. But another reason is that I’m skeptical that anyone actually comes to believe the JFK conspiracy hypothesis because they don’t see how the second bullet came in at the appropriate angle to pass through JFK’s neck and shoulder and then hit Governor Connally. Clear up some technical point (or ten or fifty of them)—as has been done over and over—and the believers will simply claim that the data you used was altered by the CIA, or they’ll switch to other “anomalies” without batting an eye. Instead, people start with certain general beliefs about how the world works, “who’s really in charge,” what sorts of explanations to look for, etc., and then use their general beliefs to decide which claims to accept about JFK’s head wounds or the foliage in Dealey Plaza—not vice versa. That being so, one might as well just discuss the general beliefs from the outset. So without further ado, here are my twenty reasons:

1. Conspiracy theorizing represents a known bug in the human nervous system. Given that, I think our prior should be overwhelmingly against anything that even looks like a conspiracy theory. (This is not to say conspiracies never happen. Of course they do: Watergate, the Tobacco Institute, and the Nazi Final Solution were three well-known examples. But the difference between conspiracy theorists’ fantasies and actual known conspiracies is this: in a conspiracy theory, some powerful organization’s public face hides a dark and terrible secret; its true mission is the opposite of its stated one. By contrast, in every real conspiracy I can think of, the facade was already 90% as terrible as the reality! And the “dark secret” was that the organization was doing precisely what you’d expect it to do, if its members genuinely held the beliefs that they claimed to hold.)

2. The shooting of Oswald by Jack Ruby created the perfect conditions for conspiracy theorizing to fester. Conditioned on that happening, it would be astonishing if a conspiracy industry hadn’t arisen, with its hundreds of books and labyrinthine arguments, even under the assumption that Oswald and Ruby both really acted alone.

3. Other high-profile assassinations to which we might compare this one—for example, those of Lincoln, Garfield, McKinley, RFK, Martin Luther King Jr., Gandhi, Yitzchak Rabin…—appear to have been the work of “lone nuts,” or at most “conspiracies” of small numbers of lowlifes. So why not this one?

4. Oswald seems to have perfectly fit the profile of a psychopathic killer (see, for example, Case Closed by Gerald Posner). From very early in his life, Oswald exhibited grandiosity, resentment, lack of remorse, doctrinaire ideological fixations, and obsession with how he’d be remembered by history.

5. A half-century of investigation has failed to link any individual besides Oswald to the crime. Conspiracy theorists love to throw around large, complicated entities like the CIA or the Mafia as potential “conspirators”—but in the rare cases when they’ve tried to go further, and implicate an actual human being other than Oswald or Ruby (or distant power figures like LBJ), the results have been pathetic and tragic.

6. Oswald had previously tried to assassinate General Walker—a fact that was confirmed by his widow Marina Oswald, but that, incredibly, is barely even discussed in the reams of conspiracy literature.

7. There’s clear evidence that Oswald murdered Officer Tippit an hour after shooting JFK—a fact that seems perfectly consistent with the state of mind of someone who’d just murdered the President, but that, again, seems to get remarkably little discussion in the conspiracy literature.

8. Besides being a violent nut, Oswald was also a known pathological liar. He lied on his employment applications, he lied about having established a thriving New Orleans branch of Fair Play for Cuba, he lied and lied and lied. Because of this tendency—as well as his persecution complex—Oswald’s loud protestations after his arrest that he was just a “patsy” count for almost nothing.

9. According to police accounts, Oswald acted snide and proud of himself after being taken into custody: for example, when asked whether he had killed the President, he replied “you find out for yourself.” He certainly didn’t act like an innocent “patsy” arrested on such a grave charge would plausibly act.

10. Almost all JFK conspiracy theories must be false, simply because they’re mutually inconsistent. Once you realize that, and start judging the competing conspiracy theories by the standards you’d have to judge them by if at most one could be true, enlightenment may dawn as you find there’s nothing in the way of just rejecting all of them. (Of course, some people have gone through an analogous process with religions.)

11. The case for Oswald as lone assassin seems to become stronger, the more you focus on the physical evidence and stuff that happened right around the time and place of the event. To an astonishing degree, the case for a conspiracy seems to rely on verbal testimony years or decades afterward—often by people who are known confabulators, who were nowhere near Dealey Plaza at the time, who have financial or revenge reasons to invent stories, and who “remembered” seeing Oswald and Ruby with CIA agents, etc. only under drugs or hypnosis. This is precisely the pattern we would expect if conspiracy theorizing reflected the reality of the human nervous system rather than the reality of the assassination.

12. If the conspiracy is so powerful, why didn’t it do something more impressive than just assassinate JFK? Why didn’t it rig the election to prevent JFK from becoming President in the first place? (In math, very often the way you discover a bug in your argument is by realizing that the argument gives you more than you originally intended—vastly, implausibly more. Yet every pro-conspiracy argument I’ve read seems to suffer from the same problem. For example, after successfully killing JFK, did the conspiracy simply disband? Or did it go on to mastermind other assassinations? If it didn’t, why not? Isn’t pulling the puppet-strings of the world sort of an ongoing proposition? What, if any, are the limits to this conspiracy’s power?)

13. Pretty much all the conspiracy writers I encountered exude total, 100% confidence, not only in the existence of additional shooters, but in the guilt of their favored villains (they might profess ignorance, but then in the very next sentence they’d talk about how JFK’s murder was “a triumph for the national security establishment”). For me, their confidence had the effect of weakening my own confidence in their intellectual honesty, and in any aspects of their arguments that I had to take on faith. The conspiracy camp would of course reply that the “Oswald acted alone” camp also exudes too much confidence in its position. But the two cases are not symmetric: for one thing, because there are so many different conspiracy theories, but only one Oswald. If I were a conspiracy believer I’d be racked with doubts, if nothing else then about whether my conspiracy was the right one.

14. Every conspiracy theory I’ve encountered seems to require “uncontrolled growth” in size and complexity: that is, the numbers of additional shooters, alterations of medical records, murders of inconvenient witnesses, coverups, coverups of the coverups, etc. that need to be postulated all seem to multiply without bound. To some conspiracy believers, this uncontrolled growth might actually be a feature: the more nefarious and far-reaching the conspiracy’s tentacles, the better. It should go without saying that I regard it as a bug.

15. JFK was not a liberal Messiah. He moved slowly on civil rights for fear of a conservative backlash, invested heavily in building nukes, signed off on the botched plans to kill Fidel Castro, and helped lay the groundwork for the US’s later involvement in Vietnam. Yes, it’s possible that he would’ve made wiser decisions about Vietnam than LBJ ended up making; that’s part of what makes his assassination (like RFK’s later assassination) a tragedy. But many conspiracy theorists’ view of JFK as an implacable enemy of the military-industrial complex is preposterous.

16. By the same token, LBJ was not exactly a right-wing conspirator’s dream candidate. He was, if anything, more aggressive on poverty and civil rights than JFK was. And even if he did end up being better for certain military contractors, that’s not something that would’ve been easy to predict in 1963, when the US’s involvement in Vietnam had barely started.

17. Lots of politically-powerful figures have gone on the record as believers in a conspiracy, including John Kerry, numerous members of Congress, and even frequently-accused conspirator LBJ himself. Some people would say that this lends credibility to the conspiracy cause. To me, however, it indicates just the opposite: that there’s no secret cabal running the world, and that those in power are just as prone to bugs in the human nervous system as anyone else is.

18. As far as I can tell, the conspiracy theorists are absolutely correct that JFK’s security in Dallas was unbelievably poor; that the Warren Commission was as interested in reassuring the nation and preventing a war with the USSR or Cuba as it was in reaching the truth (the fact that it did reach the truth is almost incidental); and that agencies like the CIA and FBI kept records related to the assassination classified for way longer than there was any legitimate reason to (though note that most records finally were declassified in the 1990s, and they provided zero evidence for any conspiracy). As you might guess, I ascribe all of these things to bureaucratic incompetence rather than to conspiratorial ultra-competence. But once again, these government screwups help us understand how so many intelligent people could come to believe in a conspiracy even in the total absence of one.

19. In the context of the time, the belief that JFK was killed by a conspiracy filled a particular need: namely, the need to believe that the confusing, turbulent events of the 1960s had an understandable guiding motive behind them, and that a great man like JFK could only be brought down by an equally-great evil, rather than by a chronically-unemployed loser who happened to see on a map that JFK’s motorcade would be passing by his workplace. Ironically, I think that Roger Ebert got it exactly right when he praised Oliver Stone’s JFK movie for its “emotional truth.” In much the same way, one could say that Birth of a Nation was “emotionally true” for Southern racists, or that Ben Stein’s Expelled was “emotionally true” for creationists. Again, I’d say that the “emotional truth” of the conspiracy hypothesis is further evidence for its factual falsehood: for it explains how so many people could come to believe in a conspiracy even if the evidence for one were dirt-poor.

20. At its core, every conspiracy argument seems to be built out of “holes”: “the details that don’t add up in the official account,” “the questions that haven’t been answered,” etc. What I’ve never found is a truly coherent alternative scenario: just one “hole” after another. This pattern is the single most important red flag for me, because it suggests that the JFK conspiracy theorists view themselves as basically defense attorneys: people who only need to sow enough doubts, rather than establish the reality of what happened. Crucially, creationism, 9/11 trutherism, and every other elaborate-yet-totally-wrong intellectual edifice I’ve ever encountered has operated on precisely the same “defense attorney principle”: “if we can just raise enough doubts about the other side’s case, we win!” But that’s a terrible approach to knowledge, once you’ve seen firsthand how a skilled arguer can raise unlimited doubts even about the nonexistence of a monster under your bed. Such arguers are hoping, of course, that you’ll find their monster hypothesis so much more fun, exciting, and ironically comforting than the “random sounds in the night hypothesis,” that it won’t even occur to you to demand they show you their monster.

Further reading: this article in Slate.