Even if you know how to defend yourself against one person, fighting several people is a hugely different situation. You could be a Golden Gloves champion, but while you confront your first attacker, you'll have one or more people taking your flank. Underestimating the gravity of this problem is one of the more dangerous illusions that martial artists acquire. It is true that uncommitted or unsophisticated attackers might approach you serially, and if you have good skills, you might prevail over one at a time. But if you're swarmed by several people at once, it becomes a problem for which no martial art has a solution. Only having a weapon makes you likely to prevail.

Similarly, a knife attack is always a disaster for an unarmed person. Somebody who gets out of 10 years in a maximum-security prison has basically gone to graduate school for shanking people. A person who is seriously intent upon killing you with a knife is not going to attack in the way you've learned to expect from martial-arts class. Most martial artists have done knife-defense drills where their partners attack in a very stereotyped way--lunging forward with a single thrust and leaving their arm out there so that you can perform the technique. This is just a pantomime of combat, and it is dangerously misleading.

The reality of a knife attack is that even if you stop 50% of the thrusts and slashes, you will be taking damage with every other move. And getting cut with a knife of any size is physiologically horrible in a way that few people realize. It is arguably worse than getting shot. A bullet is a tiny ball of metal that may or may not hit something vital. Unless you're shooting someone in the brainstem or heart, you're basically waiting for blood loss to incapacitate him. A knife--especially in the hands of someone who knows how to use it--cuts through everything it touches, and it's not going to malfunction or run out of bullets. It is also much harder to wrestle a blade out of a person's hand, because you can grab a gun without getting your fingers cut off.

A book called Put 'Em Down, Take 'Em Out!: Knife Fighting Techniques From Folsom Prison is one of the scariest things I've ever read, and it put the fear of knives into me. But I also wasn't sure I wanted to be the type of person who thought about this stuff too much. I liked being able to walk around the world without imagining arterial blood spraying from my body. Does it ever bother you to think about self-defense so much?

You can think about these facts sparingly, and still be motivated by them, without being morbid. To take violence at a totally different scale: A person can read Jonathan Schell's The Fate of the Earth, which describes the horrific reality of a nuclear exchange between the U.S. and Russia, put the book back on the shelf, and remember the punchline: that a full-blown nuclear war would be so unimaginably bad that it must be avoided at all costs. It's useful to have visited these cantos of hell, however briefly, to have an intelligent understanding of the realities involved. An obsession with self-defense can seem paranoid, especially if you live in a safe part of the developed world. The vast majority of us are never going to confront real violence, as long as we don't stupidly seek it out. But when you look at the statistics related to violent crime, you might be surprised to discover that it's not like worrying about a plane crash. It's more like worrying about a car accident. I've never been in a serious car accident, but I don't consider it irrational to view driving as intrinsically dangerous. Once you go down the rabbit-hole and admit that certain self-defense skills are worth having, you discover that it can be immensely fun to acquire them. The reality of what you're learning is pretty grim when you look at its possible application in the real world, and a person can certainly become slightly aberrated by spending too much time thinking about violence. But there's nothing morbid about training in the martial arts--or even with guns, knives, and other weapons.

Have you ever encountered real-world violence?

Not in any significant way. Once, as a freshman at Stanford, I came upon three guys abusing a dog tethered to a parking meter. Unfortunately, I had spent the day drinking with friends and had about five watts of situational awareness, so I was in no condition to defend myself or the dog. But I tried to reason with them. The next thing I knew, I was coming to, after having been hit in the head. I was out of the fight before I even realized I was in it. Of course, given what I just said about the problem of multiple attackers, I'm not sure the situation would have been much different had I been sober.

You've mentioned that having a family has made you more aware of personal security. Has it had any effect on how you think about religion? Daniel C. Dennett, who as a very young boy lost his father, has said that the ability of parents to console grieving children through religion is perhaps sufficient in itself to explain the survival of religious belief.

Religion provides the only story that is fundamentally consoling in the face of the worst possible experiences--the death of a parent, for instance. In fact, many religions take away the problem entirely, because their adherents ostensibly believe that they're going to be reunited with everyone they love, and death is an illusion. There is no rational substitute for that consolation, and I think we atheists need to admit this.

But we can leave that aside, along with everything else we abandon in childhood, and be no poorer for it. There is a shadow to false comfort, because it prevents people from dealing honestly with grief and loss. If you really believe your loved one is on the right hand of Jesus, there is nothing to grieve for. I've heard from people who [said] the support they received from their religious friends often seemed to be a way of avoiding the reality of their suffering. To say something like, "She's in a better place" strikes me as total failure of compassion. It is a false claim to knowledge motivated by one's own fear of death--and by one's discomfort in the presence of another's pain.

There is much more wisdom and compassion in accepting the magnitude of another person's loss, and of our own inevitable losses, without pretending to know things we don't know. As a parent, it's my responsibility to equip my child to do this--to grieve when grief is necessary and to realize that life is still profoundly beautiful and worth living despite the fact that we inevitably lose one another and that life ends, and we don't know what happens after death.

Yanagi Ryuken, an aikido practitioner in Japan, managed to convince many people -- himself among them -- that he had mastered the "no-touch knockout": an ability to vanquish his opponents without even touching them. The first of these two videos, which you've featured in your essay about Brazilian jiu-jitsu, "The Pleasures of Drowning," shows Yanagi effortlessly thwarting dozens of his students as they appear to attack him:

In the second video, he confronts a martial artist not in on the delusion, and that second martial artist punches Yanagi in the face.

Yanagi's students seem to be under some kind of spell. Why would they be willing to go along with Yanagi's charade for so long? Are we seeing a phenomenon like religion?

Those videos defy description. They are the physical manifestation of the same kinds of reasoning errors and self-deception we see in religion--with the crucial difference that, in martial arts, it is possible to expose a person's misconceptions in real time for all to see. But what's amazing--and this should really worry people of faith--is that, even in the martial arts, a person can persist in delusion for decades, gather students, and become a famous master of his fake discipline without knowing that he has wandered completely out of contact with reality. This madman can't even begin to do what he thinks he can do--and what he is apparently renowned for doing--because the skill he is displaying and that his students are striving to emulate doesn't exist. The whole thing is a collective delusion. If religion were a sport, it would look like that first Yanagi Ryuken video. The second video, of course, is what science has been doing to religion, over and over, for the last few centuries.

It's a little hard to see how Yanagi's delusion got up and running, but once everyone began falling all over themselves, it is easy to see how it was maintained. Imagine it from his point of view: if you thought you might be able to knock people down at a distance, and then your students complied and fell down on cue, year after year, you might begin to believe that you really had these powers. To a lesser extent, this is a problem in many martial arts: because to train most techniques without getting hurt, you have to allow little elements of fantasy to creep in. Does poking someone in the eye really end a fight? People who have done this in combat probably know, but millions of martial artists pretend to poke each other in the eyes throughout their training, without ever knowing what would happen if they tried it for real. You can't train with real knives, because you'd get killed on the first day. So you train with plastic or rubber knives, and you begin to lose sight of just how far you've departed from realism. This happens to some degree no matter how tactically sound the instruction is.

Of course, in Yanagi's case, it is harder to see how a new student would suddenly get knocked off his feet based by virtue of his own self-deception. But there's so much social pressure to confirm the stated dogma. It's not that people need to fake these things consciously. They can be led by a stepwise process to fake it without ever having to confront the fact that they're faking. It is like faith healing or speaking in tongues. A person can be inducted into a performance by the performances of others.

You've studied with experts in martial arts, such as Ryron Gracie in Brazilian jiu-jitsu, and with experts in meditation, such as Tulku Urgyen Rinpoche. Do experts in these two fields have anything in common?

Ryron strikes me as a very meditative person, although I don't know if he's practiced meditation. Some BJJ instructors are hard-charging, high testosterone, and thuggish. But Ryron is about the nicest guy you will ever meet. There's something about BJJ as a martial art that strikes a tangent to the more contemplative project of self-transcendence. In BJJ, one's ego-centric illusions get cancelled right at the outset. You can't fake being good at BJJ for even 30 seconds. As you train, you are constantly haunted by the evidence of someone else's superior skill. There's also something meditative about the experience of rolling--which is what sparring is called in BJJ--although it's by no means a straightforward way to meditative insight.

When you are in the presence of a real master of meditation, his skills are not so apparent. And if everyone around this person is behaving like he's the messiah, the room for self-deception is obvious. Spiritual life can certainly follow the pattern one sees in the fake martial arts, with most teachers making nebulous and magical claims that never get tested, while their students derange themselves with weird ideas, empty rituals, and other affectations. Nevertheless, meditation is a skill that can be taught. Self-transcendence is a repeatable experiment.

Here's one way of describing the experiment: Pay close enough attention to the nature of your own mind--to the flow of thoughts, moods, sensations, and perceptions in the present--and you can notice that the feeling of being a self, an ego, a thinker of thoughts in the midst of experience, is an illusion. Which is to say that you can actually discover the absence of the feeling that you call "I". You still have thoughts, moods, sensations, perceptions, but there it will be clear that there is no self riding around in your head owning these experiences. This is a discovery that can be made, and it's every bit as reproducible and confirmable as the proper technique for applying a triangle choke.

My own experience with meditation brought me unexpected calm and serenity. But I found that it disarmed me analytically, and banished a lot of thoughts that I usually think of as productive. Does meditation conflict with productive thinking?

No. Your mind will be active in any case, no matter how much you meditate. The goal is not to be without thought, but to be aware of the character of your experience in each moment and not suffer unnecessarily. Almost all our suffering is the product of our thoughts. We spend nearly every moment of our lives lost in thought, and hostage to the character of those thoughts. You can break this spell, but it takes training just like it takes training to defend yourself against a physical assault. You are thinking every moment and not aware of it, and the initial experience of anyone who seriously tries to meditate is one of discovering how incessant this cascade of thoughts is.

It's probably true that certain human accomplishments depend upon people's neurotic needs for achievement or their lust for money or power. A lot of art comes from a place of being captivated by selfish illusions. And if a person were to permanently dispel the illusion of the self, he might not write great novels or start the next Apple. Buddhahood might be incompatible with being the next Nabokov or Steve Jobs. Luckily, no one has ever had to choose between becoming a great artist or entrepreneur, or the next Buddha.

The relevant question for me is how neurotic and unhappy and self-deceived do we have to be while living productive lives. I think the general answer is, far less than most of us are.

Your career as one of the New Atheists has involved getting in what most would describe as unwinnable fights, arguing with opponents who will simply never agree with you. Most people, when confronted with maddeningly stubborn opponents, just shrug and move on. Do you think that your willingness to fight is a sign of a fundamentally unquiet mind? Maybe you need meditation more than most of us.

It's easy to misunderstand the situation - intellectually, ethically, and psychologically - from the outside. These fights are actually not unwinnable. I constantly discover what it looks like to win. It's just rarely visible to those who are watching the fight. For instance, if I do a public debate with a rabbi or a pastor or some other representative of Iron Age philosophy, I know he isn't going to change his mind while talking to me in front of a thousand people. But then I hear from those who watch these debates and have their views change completely. And this includes people who might have been just as incorrigible as my debate opponent in another context--rabbis, pastors, priests, life-long fundamentalists, etc.

Minds can change. And even whole cultures can change, radically and quickly. Once we understand human well-being better than we do and begin talking about the full range of spiritual experience in the context of a rational, empirical, evidence-based view of the universe, people will see that there really is no game worth playing that is best played in a church, synagogue, or mosque.

No one's ever accused me of being an optimist, but I think reason and intellectual honesty will win. They're just too useful.

Don't miss Graeme Wood's profile of Sam Harris in the May issue of The Atlantic.